LU102117A1

LU102117A1 - Method and system for measuring mountain view visible area in city

Info

Publication number: LU102117A1
Application number: LU102117A
Authority: LU
Inventors: Junyan Yang; Jun Cao; Yingchen Liu; Qingyao Zhang; Zhicheng Liu; Qiao Wang
Original assignee: Univ Southeast
Priority date: 2019-03-28
Filing date: 2020-02-27
Publication date: 2020-10-19
Also published as: LU102117B1; WO2020192355A1; CN109883401A; CN109883401B; WO2020192026A1

Abstract

The invention discloses a method and system for measuring a mountain view visible area in a city. The system includes the following modules: an integral database scene construction module used for acquiring a digital model including a mountain and a city area through oblique photography and actual measurement; an observation area full-surface rasterization module used for extracting an observation area and rasterizing a model surface; an observation point spherical coordinate system creation module used for setting an observation point and creating a spherical coordinate system according to a sightline angle; a mountain effective projection plane cutting module used for cutting out a mountain effective projection plane in the spherica coordinate system; a mountain view sightline blocking computation module used for generating a mountain view sightline and computing whether the sightline is blocked or not; and a data output and imaging module used for outputting mountain view visible area data and imaging to generate a mountain view visible area map.

Description

METHOD AND SYSTEM FOR MEASURING MOUNTAIN VIEW VISIBLE AREA INU102117

CITY Technical Field The invention belongs to the field of city planning, and in particular to a method and system for measuring a mountain view visible area in the city. Background Art Mountain view visible area, also referred to as mountain view visible area range, mountain view visibility, mountain view visible rate, mountain view visible factor and so on, refers to a geographical range that the mountain terrain can be seen by a line of sight of a single observer in the built environment. It reflects the publics’ visibility of the natural mountain landscape elements in the built environment, and relates to the spatial feeling and comfort level of city public life. In city planning and design, using the quantitative results of the mountain view visible area as an indicator is helpful to the city planning and design decisions, and meanwhile can also be used as an important basis for city spatial layout control and optimization. By optimizing the mountain view visible area in the current city space environment, the perception of mountain landscape can be effectively strengthened, and the quality of city space may be improved, so that the publics may "see mountains and water" in the city, thereby entirely achieving a state of harmony between the city and nature. According to the standard image that reflects the visual perception of the mountain from a certain viewpoint in the city built environment, analyzing and computing the accurate value of the visible area of the mountain is the first and important technical link for the city planning and construction department to control the mountain view visible area. The existing measurement technologies for the mountain view visible area include on-site field measurement technology and street view image visible area measurement technology. The on-site field measurement technology refers to using a digital camera with a fisheye lens to take digital photos for an open space at a determined point of view as the image source for measurement, and further extracting the mountain part of the photos through the channels and level adjustment tools in the Photoshop software, and obtaining the mountain view visible area by computing the proportional relationship between the mountain part and the other parts of th&/102117 image. The street view image visible area measurement technology refers to sampling street view images on the map sites such as Baidu Street View and Tencent Street View, and further automatically recognizing the mountain elements in the images via the computer based on the artificial intelligence image recognition technology, and obtaining a numerical value of the mountain view visible area by computing the proportional relationship between the mountain elements and other elements except the mountain elements in a single street view image via the computer. In essence, the above methods belong to the analysis and computation of the scene images, and have the advantages that the operations are simple and efficient, the mountain elements may be intuitively divided through current photos and street view scene images, the proportion between the mountain elements and other city elements may be calculated to obtain the mountain view visible area, and in the actual operation of a single image, it is easy to handle and may be analyzed and calculated efficiently.

However, compared with the method for measuring the mountain view visible area proposed by the present invention, the current three main measurement methods have limitations in the view point area that may be measured. When selecting the view point of the mountain view visible area, for the field measurement technology, the actual surveyor’s selection of the location has a certain degree of subjectivity, and often selects the appropriate point and perspective according to the on-site judgment, and for the street view image visible area measurement technology, street view images only contain visual images of city street space, and their data volume cannot cover lower-level roads in the city, and meanwhile also ignore the potential mountain view points such as other grounds, building facades and roofs in city space.

Summary of Invention The purpose of the invention: in view of the above problems, the present invention proposes a method and system for measuring a mountain view visible area in a city, which can measure the mountain view visible area in the city on the entire surfaces including urban roads, urban blocks, building facades, building roofs, etc., as observation points within a given city,

thereby avoiding the limitations of the existing measurement technology in the selection 8102117 observation points; creating a spherical coordinate system according to a boundary of the visual field of the observation point, cutting out a mountain effective projection plane in the spherical coordinate system, generating a mountain view sightline and computing whether sightline is blocked, which effectively improve the measurement accuracy of the mountain view visible area and avoid the problems of low accuracy and low work efficiency in the traditional measurement methods; outputting the mountain view visible range data and imaging to finally generate a mountain view visible area map, thus the effect is more intuitive, which provides a basic rational support for further analysis and decision in the city planning and design.

Technical solution: in order to achieve the purpose of the present invention, the technical solution adopted by the present invention is: a method for measuring a mountain view visible area in a city, including the following steps: (1) collecting and constructing a real three-dimensional model scene comprising a mountain and a city area; (2) extracting an observation area and rasterizing a model surface; (3) setting an observation point and creating a spherical coordinate system according to a sightline angle; (4) cutting out a mountain effective projection plane in the spherical coordinate system; (5) generating a mountain view sightline and computing whether sightline is blocked; (6) outputting the mountain view visible area data and imaging to generate a mountain view visible area map.

Further, in step (1), a method for collecting and constructing the real three-dimensional model scene comprising a mountain and the city area specifically comprises: (1.1) acquiring the oblique photography data comprising the mountain and the city area through actual measurement The oblique photography measurement is to collect images of 1 vertical angle and 4 tilt angles at the same time by mounting a multi-lens camera group on a flying platform,such as a multi-rotor drone, a fixed-wing drone, a vertical take-off and landing drone or the like.

(1.2) generating, according to the acquired oblique photography data, a real three-

dimensional model based on real image texture, LU102117 Oblique photography automated modeling software geometric correction, joint adjustment, multi-view image matching and other series of processing to obtain all-round information of the ground feature data to generate a real three-dimensional model; the automated modeling software may be the VirtualGeo software developed by the French DIGINEXT company,the EFSelectronic Field Study software of the US Pictometry company.

(1.3) loading the real three-dimensional model acquired from the oblique photography data through a SuperMap platform The SuperMap platform uses LOD (Level of Detail) to optimize scheduling, only occupies less hardware resources, guarantees stable mass data carrying capacity, and meanwhile supports the direct loading of oblique photography models of any subdivision type, including formats such as .osg/.osgb, .x, .dae, and .obj;the platform may generate a plurality of * osgb format oblique photography model data stored in a plurality of folders into *.scp format files through the generation configuration file function;this file records the relative path, name, insertion point position and coordinate system information of the oblique photography model file; and the platform realizes the direct batch loading and browsing of the OSGB model data by loading the three-dimensional model cache file in *.scp format.

Further, in step (2), a method for extracting the observation area and rasterizing a model surface specifically comprises: (2.1) Observation area extraction, extracting the observation area from the real three- dimensional model obtained by loading the oblique photography on the SuperMap platform, here selecting the area to be observed from the large area, and observing the mountain from the observation area.

(2.2) rasterizing an entire surface of the observation area in the real three-dimensional model, the grid method is to rasterize the three-dimensional city model in the real three- dimensional model including the ground, building facade, and roof in unit square meter. In the process of raster conversion, the selection of the grid unit size is very critical: if the grid unit size is too large, the analysis accuracy will decrease; on the contrary, if the grid unit size is too small, the time consumption cost of subsequent visual field analysis will increase. Therefore, it is necessary to comprehensively determine the size of the basic grid unit based on the collectéd)102117 data volume, data accuracy and target analysis accuracy.

In the actual operation, for example, the unit square meter may be selected as a basic unit accuracy.

Further, in step (3), a method for setting the observation point and creating the spherical 5 coordinate system according to a sightline angle specifically comprises: (3.1) setting coordinates of the observation point, and selecting a geometric center point of each grid as an observation point representing the grid; (3.2) creating the spherical coordinate system to convert an observer in city space into the observation point in three-dimensional space O(x,,¥,,Z,), that is a grid observation point, wherein (x,,y,) is a value of a plane coordinate where the observer is located, and z, is a horizontal plane height of the observation point; taking the horizontal plane V, at the height of the observation point as a plane, and taking a maximum visible distance Rymax in a current environment as a radius to make a visible hemisphere, and defining the hemisphere as a standard projection plane P,; taking the observation point O(x,,¥,,Z,) as a sphere center, and separately taking a due north direction in a geographic coordinate system and a vertical direction of the horizontal plane V, as vector bases to establish the spherical coordinate system (r,0,@). The current environment may be the environment such as current air, sunlight, etc. (3.3) determining a boundary of the visual field.

Setting that the observation range of the observation point O is restricted by obstacles or other objective reasons, causing the observer at the observation point to only observe the landscape within a certain angle range.

This angle range is defined as the boundary of the visual field.

Recording angle values a, and ßo between the boundary of the visual field and the vector bases in the due north direction of the spherical coordinate system.

For example, if the visual field of an observation point is between the due north direction and the due south direction, an attribute value of the observation point is (0, 7). Further, in step (4), a method for cutting out the mountain effective projection plane in the spherical coordinate system specifically comprises: In this spherical coordinate system, passing points (Rymax» 0, @,) and (0,0,0) to make a plane V, perpendicular to the horizontal plane Vj; similarly, passing points (Rymax 0, Bo)

and (0,0,0) to make a plane Vg perpendicular to the horizontal plane V,. The area whet&/102117 the standard projection plane Ps is cut by the plane Vg and the plane V,, is defined as the standard effective projection area P.. The projection of the mountain on the standard effective projection area P, is the standard effective mountain projection.

It should be noted that due to the limitation of calculation amount in the process of projecting complex curved surfaces onto spherical surfaces, in practical applications, the standard projection planes are often approximated to a certain extent. In the spherical coordinate system, making a projection P, of the mountain on the horizontal plane V,, taking the point with the largest distance from the observation point in the projection P, and recording coordinates of the point as (r,, 0, @;), wherein meanwhile, 7, is a distance from the point to the observation point,¢, is an angle between a line connecting the point and the observation point and a coordinate axis in the due north direction. Taking an angle bisector of the boundary of the visual field of the observation point on the horizontal plane V,, the angle bisector intersecting a standard projection plane P, at a point (Romax» 0,0.5(a, + Bo). If rp > Rvymax» Making a plane P, tangent to the standard projection plane P, in a mode of passing through the point (Romax» 0,0.5(œ, + Bo), wherein P, is an approximate projection plane; if Te < Rymax;taking the horizontal plane V at the height of the observation point as the plane and taking 7, as a radius to make a reference hemisphere C,, and then passing through the point (r,,0,@;) to make a plane P, tangent to the reference hemisphere C,, wherein P, is the approximate projection plane. On the approximate projection plane P,, making straight lines perpendicular to the horizontal plane V, in a mode of separately passing through (min(Rymax Te), 0, a5) and (min(Rymax Te), 0, Bo), wherein an area where the approximate projection plane P, 1s cut out by two straight lines 1s an approximate effective projection area P.a- For the area at 2/3 or more of a height of the mountain, making its projection on the approximate effective projection area P.,, wherein the projection is an approximate effective mountain projection.

Further, in step (5), generating the mountain view sightline and computing whether sightline is blocked are specifically as follows:

(5.1) generating the mountain view sightline LU102117 The projection on the approximate effective projection area F,, is used to illustrate the following steps.

Rasterizing the effective mountain projection in m Xn rectangular grid areas,taking a grid center point in a lower left corner as an origin, establishing an orthogonal coordinate system Ç on the approximate effective projection area P,,, and simplifying the rasterized effective mountain projection into a point set {N; (xq, v1), N2(x2, V2), +++, Ns(Xs, Vs) } composed of the center points of these grids.

Wherein, (x1, V1), (X2, V2), +++, (x5, Ys) is the discrete coordinates of the points in a two-dimensional orthogonal coordinate system Ç after the mountain projection being rasterized into the point set,0 < x; < m, O0 < y; En, 1<i< §,Sis the total number of center points of the grids.

The connecting line from the observation point O to the point Ny, N,,---, N, is recorded as sightline L,, L,,--, L,. In addition, the center point of each grid has a weight w;, wherein, 0 < w; < 1. If it is needed to emphasize the iconic landscape on the mountain, the weight of the point set related to the iconic landscape on the mountain may be increased.

If not, generally, it is considered w, = w, = + = w, = 1. The size of the basic grid unit needs to be considered comprehensively according to the computing environment, data quality, and accuracy requirements. (5.2) Computing the sightline blocking computing whether sightline is blocked, and defining an algorithm called bisection line of sight calculation.

The steps of the algorithm are as follows: Step 1: retrieving the point with an abscissa of © in the point set {N (xq, v1), No(x2, V2), +++, N5(Xs, Ys)}, and recording the subset composed of the retrieved points as {N;(0,v,),, N; (0, Vomax)}, Wherein j is the total number of points with the abscissa of 0, and the point with the largest ordinate at the abscissa of 0 is recorded as Nomax-Yomax 18 the value of the ordinate of Nomax; step 2: determining whether sightline Lomax corresponding to the point Nomax 1s blocked, if sightline Lomax 1S blocked, then sightline corresponding to all the points with the abscissa of 0 in the point set {N (x, v1), N7(X2, V2), ++, Ns(xs, Ys)} is recorded as being blocked; if sightline Lomax 1S not blocked, going to step 3; LU102117 step 3: establishing a balanced binary search tree with points in the set {N,(0, yi), +, N;(0, Vomax)} the value of each node in the balanced binary search tree being the value of the ordinate of each point in the set, and traversing the nodes in the balanced binary search tree: step 4: whenever traversing one node, computing whether sightline corresponding to the node 1s blocked, and recording an attribute of whether sightline corresponding to the node is blocked in alist; if sightline corresponding to the node is not blocked, continuing to traverse the left subtree thereof, and defining sightline corresponding to the node and all points on the right subtree of the node as being unblocked, if sightline corresponding to the node is not blocked, defining sightline corresponding to the node and all points on the left subtree of the node as being unblocked, and computing whether sightline corresponding to the right sub-node of the node is blocked: if sightline corresponding to the right sub-node of the node is not blocked, defining sightline corresponding to the remaining unmarked nodes as being unblocked, and stopping the traversal; if sightline corresponding to the right sub-node of the node has been blocked, continuing to traverse the right subtree thereof; in the process of traversing the nodes, if encountering one node that has been marked whether the corresponding line of sight is blocked, directly reading a result of whether its corresponding line of sight is blocked from the list, and stopping the traversal when whether the sight lines corresponding to all nodes are blocked is marked; step 5: retrieving points with an abscissa of k in the point set {N (xy, v1), No(x2, V2), +++, N5(X5, Ys)}, wherein, 0 < k < m, recording the subset comprised of the retrieved points as {N;(k yy), >, N;(k, Vimax)},Wherein,j is the total number of points with the abscissa of k, point with the largest ordinate is recorded as Nemax»Ykmax1$ à value 68102117 the ordinate of Nkmax- determining whether sightline Lemax corresponding to the point Nymax 18 blocked.

If sightline Lemax1S blocked, recording sightline corresponding to all points with the abscissa of k in the point set {N, (xy, V4), N2(xz, V2), ++, N5(Xs, Ys)} as being blocked.

If sightline Limax 1S not blocked, establishing a balanced binary search tree with points in the set {N,(k, yi), +, N;(k, Vmax) } the value of each node in the balanced binary search tree being the value of the ordinate of each point in the set, and traversing the nodes in the balanced binary search tree, going to step 4. step 6: taking k = 1,k = 2, ---,k = m respectively and repeating the step 5 to complete the computation of whether all sightlines L;,L,, +, Ls are blocked.

Further, in step (6), a method for outputting the mountain view visible area data and imaging to generate the mountain view visible area map specifically comprises: (6.1) computing a numerical value of the mountain view visible area For the line of light Lie{L,, L,, ++, Lg}, if L; is marked as being blocked, assigning an attribute value u; = 0 to L;, and if L; is marked as being unblocked, assigning an attribute value u; = 1 to Lj.

Defining a MVF value, MVF = ak aka Dale wherein a value range of MVF is [0,1], which represents a mountain view visible rate of the observer at a certain observation point under certain atmospheric visibility constraints. (6.2) imaging via color Setting a point on a three-dimensional map as an observation point, computing a value of the mountain view visible rate in real time by inputting a maximum visible distance and an observer's visual field angle range.

In addition, the gradient color bar is set, such as green corresponding to 1(completely visible), and white representing 0 (completely invisible).color is extracted according to the MVF value, and after computer calculation, a plurality of observation areas on the three-dimensional map may be rendered with color characterized by the mountain view visible rate.

That is, color of the grid corresponding to the observation point is set according to the MVF value, the larger the MVF value, the darker color, the smaller the MVF value, the lighter color. (6.3) generating the mountain view visible area map

The observation area model rich in MVF value color attributes is re-placed into th&J102117 overall database scene, that is, colored grid is placed in the position corresponding to the original model.

Preferably, this patent can supplement atmospheric visibility constraints.

The atmospheric visibility value of a city is recorded as a, and if the distance of a certain ray is greater than a, the ray is directly recorded as being blocked by an object.

In addition, the present invention further provides a system for measuring a mountain view visible area in a city, the system comprising the following modules: an integral scene construction module, collecting and constructing a real three-dimensional model scene comprising a mountain and a city area; an observation area full-surface rasterization module, extracting an observation area and rasterizing a model surface; an observation point spherical coordinate system creation module, setting an observation point and creating a spherical coordinate system according to a boundary of the visual field; a mountain effective projection surface cutting module, cutting out a mountain effective projection plane in the spherical coordinate system; a mountain view sight blocking computation module, generating a mountain view sightline, and computing whether sightline is blocked, a mountain view sight blocking computation module, generating a mountain view sightline, and computing whether sightline is blocked.

Further, the specific functions of the integral scene construction module are as follows: (1.1) acquiring oblique photography data comprising the mountain and the city area through actual measurement, (1.2) generating, according to the acquired oblique photography data, a real three- dimensional model based on real image texture,; (1.3) loading the real three-dimensional model acquired from the oblique photography data through a SuperMap platform.

Further, the specific functions of the observation area full-surface rasterization module are as follows:

(2.1) extracting the observation area, extracting the observation area from the real threbd102117 dimensional model obtained by loading oblique photography on the SuperMap platform to observe the mountain; (2.2) rasterizing an entire surface of the observation area in the real three-dimensional model.

Further, the specific functions of the observation point spherical coordinate system creation module are as follows: (3.1) setting coordinates of the observation point, and selecting a geometric center point of each grid as an observation point representing the grid; (3.2) creating the spherical coordinate system to convert an observer in city space into the observation point in three-dimensional space O(x,,¥,,Z,), that is a grid observation point, wherein (xo, Vo) is a value of a plane coordinate where the observer is located, and z,is a horizontal plane height of the observation point; taking the horizontal plane V, at the height of the observation point as a plane, and taking a maximum visible distance Rymax in a current environment as a radius to make a visible hemisphere, and defining the hemisphere as a standard projection plane P,; taking the observation point O(x,,¥,,Z,) as a sphere center, and separately taking a due north direction in a geographic coordinate system and a vertical direction of the horizontal plane V, as vector bases to establish the spherical coordinate system (r, 6,9); (3.3) recording angle values a, and B, between the boundary of the visual field of the observation point and the vector bases in the due north direction of the spherical coordinate system.

Further, the specific functions of the mountain effective projection plane cutting module are as follow: in the spherical coordinate system, making a projection P, of the mountain on the horizontal plane V,, taking the point with the largest distance from the observation point in the projection P, and recording coordinates of the point as (7, 0, ¢.), wherein meanwhile, 7; is a distance from the point to the observation point,p; is an angle between a line connecting the point and the observation point and a coordinate axis in the due north direction, taking an angle bisector of the boundary of the visual field of the observation point on the horizontal plane V},U102117 the angle bisector intersecting a standard projection plane Pat a point (Romax» 0,0.5(a, + Bo), if Te > Rymax, Making a plane P, tangent to the standard projection plane P, in a mode of passing through the point (Romax» 0,0.5(a, + Bo)) , wherein P, is an approximate projection plane; if 7, < R,max taking the horizontal plane V, at the height of the observation point as the plane and taking 7, as a radius to make a reference hemisphere C,, and then passing through the point (13, 0,@;) to make a plane P tangent to the reference hemisphere C,, wherein P, is the approximate projection plane; on the approximate projection plane P,, making straight lines perpendicular to the horizontal plane V, in a mode of separately passing through (min(Rymax Te), 0, a) and (min(Rymax Te), 0, Bo), wherein an area where the approximate projection plane P, is cut out by two straight lines is an approximate effective projection area P,, ;for the area at 2/3 or more of a height of the mountain, making its projection on the approximate effective projection area P,a, wherein the projection is an approximate effective mountain projection.

Further, the specific functions of the mountain view sight blocking computation module are as follows: (5.1) rasterizing the effective mountain projection in m X n rectangular grid areas, taking a grid center point in a lower left corner as an origin, establishing an orthogonal coordinate system Ç on the approximate effective projection area P,a, and simplifying the rasterized effective mountain projection into a point set {N;(xy, v1), No(xy, v5), =, No(xg, ys) } composed of the center points of these grids, wherein, (xq, V1), (x3, V2), =, (xs, Vs) is the discrete coordinates of the points in a two-dimensional orthogonal coordinate system Ç after the mountain projection being rasterized into the point set,0 < x; <m, 0<y; <n, 1<i< S,S is the total number of center points of the grids, the connecting line from the observation point O to the point N,, N,, +, N; being recorded as sightline L,, Lz, +, L,, the center point of each grid having a weight w;, wherein, 0 < w; < 1; (5.2)Computing the sightline blocking step 1: retrieving the point with an abscissa of O in the point set

{N (xq, v1), No (x4, V2), +++, N5(Xs5, Ys)}, and recording the subset composed of the retrievéd/102117 points as {N,(0, yi), +, N;(0, Vomax)} wherein j is the total number of points with the abscissa of 0, and the point with the largest ordinate at the abscissa of 0 is recorded as Nomax» and Yomax is the value of the ordinate of Nomax:

step 2: determining whether sightline Lomax corresponding to the point Nomax 1S blocked, if sightline Lomax 18 blocked, then sightline corresponding to all the points with the abscissa of 0 in the point set {N; (xy, yı), N2(x2, yo), , No(xs, V5)} is recorded as being blocked; if sightline Lomax 1S not blocked, going to step 3;

step 3: establishing a balanced binary search tree with points in the set {N,(0, yi), +, N;(0, Vomax)} the value of each node in the balanced binary search tree being the value of the ordinate of each point in the set, and traversing the nodes in the balanced binary search tree: step 4: whenever traversing one node, computing whether sightline corresponding to the node is blocked, and recording an attribute of whether sightline corresponding to the node is blocked in a list; if sightline corresponding to the node is not blocked, continuing to traverse the left subtree thereof, and defining sightline corresponding to the node and all points on the right subtree of the node as being unblocked, if sightline corresponding to the node is not blocked, defining sightline corresponding to the node and all points on the left subtree of the node as being unblocked, and computing whether sightline corresponding to the right sub-node of the node is blocked: if sightline corresponding to the right sub-node of the node is not blocked, defining sightline corresponding to the remaining unmarked nodes as being unblocked, and stopping the traversal; if sightline corresponding to the right sub-node of the node has been blocked, continuing to traverse the right subtree thereof; in the process of traversing the nodes, if encountering one node that has been marked whether the corresponding line of sight is blocked, directly reading a result of whether its corresponding line of sight is blocked from the list, and stopping the traversal when whether the sight lines corresponding to all nodes are blocked is marked; LU102117 step 5: retrieving points with an abscissa of k in the point set EN, (xq, v1), No(x2, V2), +++, N5(X5, Ys)}, wherein, 0 < k < m,recording the subset composed of the retrieved points as {N;(k y,), +, N;(k, Vimax)} » wherein, j is the total number of points with the abscissa of k, point with the largest ordinate is recorded as Nkmax» and Yımax 1S a value of the ordinate of Nrmax; determining whether sightline Lemax corresponding to the point Nkmax1S blocked, if sightline Lemax1S blocked, recording sightline corresponding to all points with the abscissa of k in the point set {N, (xq, V1), N7(*2, yo), , Ng(xs, Ys)} as being blocked; if sightline Lemax is not blocked, establishing a balanced binary search tree with points in the set {N,(k y1), +, N,(K, Ykmax)}, the value of each node in the balanced binary search tree being the value of the ordinate of each point in the set, and traversing the nodes in the balanced binary search tree, going to step 4.

step 6, taking k = 1,k = 2,---, k = m respectively and repeating the step 5 to complete the computation of whether all sightlines L,, La, +, L, are blocked.

Further, the specific functions of the data output and imaging module are as follows: (6.1) computing a numerical value of the mountain view visible area, wherein for the line of light Lie{Lq, Ly, +, Ls}, if Li is marked as being blocked, assigning an attribute value |; = 0 to Lj, and if L; is marked as being unblocked, assigning an attribute value u; = 1 to Lj; defining a MVF value, MVF = marais wherein a value range of MVF is [0,1], which represents a mountain view visible rate of the observer at a certain observation point under certain atmospheric visibility constraints; (6.2) imaging via color, setting a point on a three-dimensional map as an observation point, computing a value of the mountain view visible rate in real time by inputting a maximum visible distance and an observer's visual field angle range , and setting color of the grids corresponding tothe observation points according to the MVF value; (6.3) generating the mountain view visible area map, that is placing colored grid into a corresponding position in an original model.

Beneficial effects: compared with the prior arts, the technical solution of the present invention has the following beneficial technical effects: LU102117 The present invention proposes a method for measuring a mountain view visible area in a city, which can measure the mountain view visible area in the city on the entire surfaces including urban roads, urban blocks, building facades, building roofs, etc., as observation points within a given city, thereby avoiding the limitations of the existing measurement technology in the selection of observation points; creating a spherical coordinate system according to a boundary of the visual field of the observation point, cutting out a mountain effective projection plane in the spherical coordinate system, generating a mountain view sightline and computing whether sightline is blocked, which effectively improve the measurement accuracy of the mountain view visible area and avoid the problems of low accuracy and low work efficiency in the traditional measurement methods; outputting the mountain view visible range data and imaging to finally generate a mountain view visible area map, thus the effect is more intuitive, which provides a basic rational support for further analysis and decision in the city planning and design.

Brief Description of the Drawings Fig.1 is a technical flow chart of the digital measurement method for the mountain view visible area in the city according to the present invention; Fig. 2 is a diagram of creating a sphere coordinate system in accordance with the angle of sightline according to the present invention; Fig. 3 is a diagram of cutting a mountain effective projection plane according to the present invention; Fig. 4 is a diagram of computing the degree of the blocking to sightline of the mountain view according to the present invention.

Detailed Description of the Embodiments The technical solution of the present invention will be further described below in conjunction with the drawings and embodiments. The invention discloses a method for measuring a mountain view visible area in a city,

which comprises the following steps: LU102117 (1) collecting and constructing a real three-dimensional model scene comprising a mountain and a city area; (2) extracting an observation area and rasterizing a model surface; (3) setting an observation point and creating a spherical coordinate system according to a sightline angle; (4) cutting out a mountain effective projection plane in the spherical coordinate system; (5) generating a mountain view sightline and computing whether sightline is blocked; (6) outputting the mountain view visible area data and imaging to generate a mountain view visible area map.

(1.2) generating, according to the acquired oblique photography data, a real three- dimensional model based on real image texture, Oblique photography automated modeling software geometric correction, joint adjustment, multi-view image matching and other series of processing to obtain all-round information of the ground feature data to generate a real three-dimensional model; the automated modeling software may be the VirtualGeo software developed by the French DIGINEXT company, the EFSelectronic Field Study software of the US Pictometry company.

(1.3) loading the real three-dimensional model acquired from the oblique photography data through a SuperMap platform The SuperMap platform uses LOD (Level of Detail) to optimize scheduling, only occupies less hardware resources, guarantees stable mass data carrying capacity, and meanwhile supports the direct loading of oblique photography models of any subdivision type, including formats such as .osg/.osgb, .x, .dae, and .obj;the platform may generate a plurality of * osgb formaV102117 oblique photography model data stored in a plurality of folders into * scp format files through the generation configuration file function;this file records the relative path, name, insertion point position and coordinate system information of the oblique photography model file; and the platform realizes the direct batch loading and browsing of the OSGB model data by loading the three-dimensional model cache file in *.scp format.

(2.2) rasterizing an entire surface of the observation area in the real three-dimensional model, the grid method is to rasterize the three-dimensional city model in the real three- dimensional model including the ground, building facade, and roof in unit square meter. In the process of raster conversion, the selection of the grid unit size is very critical: if the grid unit size is too large, the analysis accuracy will decrease; on the contrary, if the grid unit size is too small, the time consumption cost of subsequent visual field analysis will increase. Therefore, it is necessary to comprehensively determine the size of the basic grid unit based on the collected data volume, data accuracy and target analysis accuracy. In the actual operation, for example, the unit square meter may be selected as a basic unit accuracy.

Further, in step (3), a method for setting the observation point and creating the spherical coordinate system according to a sightline angle specifically comprises: (3.1) setting coordinates of the observation point, and selecting a geometric center point of each grid as an observation point representing the grid; (3.2) creating the spherical coordinate system to convert an observer in city space into the observation point in three-dimensional space O(x,,¥,,Z,), that is a grid observation point, wherein (xo, Yo) is a value of a plane coordinate where the observer is located, and z, is a horizontal plane height of the observation point; taking the horizontal plane V, at the height of the observation point as a plane, and taking a maximum visible distance Rymax in a currehV102117 environment as a radius to make a visible hemisphere, and defining the hemisphere as a standard projection plane P,; taking the observation point O(x,,¥,,Z,) as a sphere center, and separately taking a due north direction in a geographic coordinate system and a vertical direction of the horizontal plane V, as vector bases to establish the spherical coordinate system (1,6, ¢). The current environment may be the environment such as current air, sunlight, etc. (3.3) determining a boundary of the visual field.

This angle range is defined as the boundary of the visual field.

Recording angle values a, and fo between the boundary of the visual field and the vector bases in the due north direction of the spherical coordinate system.

For example, if the visual field of an observation point is between the due north direction and the due south direction, an attribute value of the observation point is (0, 7). Further, in step (4), the method for cutting out the mountain effective projection plane in the spherical coordinate system specifically comprises: In this spherical coordinate system, passing points (Rymax» 0, @,) and (0,0,0) to make a plane V, perpendicular to the horizontal plane Vj; similarly, passing points (Rymax 0, Bo) and (0,0,0) to make a plane Vg perpendicular to the horizontal plane V,. The area where the standard projection plane Ps is cut by the plane Vg and the plane V,, is defined as the standard effective projection area P,. The projection of the mountain on the standard effective projection area P, is the standard effective mountain projection.

It should be noted that due to the limitation of calculation amount in the process of projecting complex curved surfaces onto spherical surfaces, in practical applications, the standard projection planes are often approximated to a certain extent.

In the spherical coordinate system, making a projection P, of the mountain on the horizontal plane V,, taking the point with the largest distance from the observation point in the projection P, and recording coordinates of the point as (13, 0, ¢,), wherein meanwhile, 7; is a distance from the point to the observation point,¢, is an angle between a line connecting the point and the observatiddJ102117 point and a coordinate axis in the due north direction.

Taking an angle bisector of the boundary of the visual field of the observation point on the horizontal plane V,, the angle bisector intersecting a standard projection plane P, at a point (Romax» 0,0.5(a, + Bo). If rp > Rymax, making a plane P, tangent to the standard projection plane P, in a mode of passing through the point (Romax» 0,0.5(a, + Bo), then P, is an approximate projection plane; if Te < Rymax-taking the horizontal plane V, at the height of the observation point as the plane and taking 7, as a radius to make a reference hemisphere C,, and then passing through the point (r,,0,@;) to make a plane P, tangent to the reference hemisphere C,, wherein P, is the approximate projection plane.

On the approximate projection plane P,, making straight lines perpendicular to the horizontal plane V, in a mode of separately passing through (min(Rymax Te), 0, a5) and (min(Rymax Te), 0, Bo), wherein an area where the approximate projection plane P, 1s cut out by two straight lines 1s an approximate effective projection area P.a- For the area at 2/3 or more of a height of the mountain, making its projection on the approximate effective projection area P,a, wherein the projection is an approximate effective mountain projection.

Further, in step (5), generating the mountain view sightline and computing whether sightline is blocked are specifically as follows: (5.1) generating the mountain view sightline The projection on the approximate effective projection area F,, is used to illustrate the following steps.

Rasterizing the effective mountain projection in m Xn rectangular grid areas,taking a grid center point in a lower left corner as an origin, establishing an orthogonal coordinate system C on the approximate effective projection area P,,, and simplifying the rasterized effective mountain projection into a point set {N; (xq, v1), N2(x2, V2), +++, Ns(Xs, Vs) } composed of the center points of these grids.

Wherein, (x1, V1), (X2, V2), +++, (x5, Ys) is the discrete coordinates of the points in a two-dimensional orthogonal coordinate system Ç after the mountain projection being rasterized into the point set, 0 < x; <m, O0 < y; €n,1<i< S,S is the total number of center points of the grids.

The connecting line from the observation point O to the point N,, N,,---, Ng is recorded as sightline L,, L,,--, L,. In addition, the center point of each grid has a weight w;, wherein, 0 < w; < 1. If it is needed to emphasik&J102117 the iconic landscape on the mountain, the weight of the point set related to the iconic landscape on the mountain may be increased. If not, generally, it is considered wı = w, = + = w, = 1. The size of the basic grid unit needs to be considered comprehensively according to the computing environment, data quality, and accuracy requirements.

(5.2)Computing the sightline blocking computing whether sightline is blocked, and defining an algorithm called bisection line of sight calculation. The steps of the algorithm are as follows: step 1: retrieving the point with an abscissa of © in the point set {N (xq, v1), No(x2, V2), +++, N5(Xs, Ys)}, and recording the subset composed of the retrieved points as {N;(0,v,),, N; (0, Vomax)}, Wherein j is the total number of points with the abscissa of 0, and the point with the largest ordinate at the abscissa of 0 is recorded as Nomax-Yomax 18 the value of the ordinate of Nomax; step 2: determining whether sightline Lomax corresponding to the point Nomax 1s blocked, if sightline Lomax 1S blocked, then sightline corresponding to all the points with the abscissa of 0 in the point set {N (x, v1), N7(X2, V2), ++, Ns(xs, Ys)} is recorded as being blocked; if sightline Lomax 1S not blocked, going to step 3; step 3: establishing a balanced binary search tree with points in the set {N.(0,y1), +, N; (0, Vomax)}, the value of each node in the balanced binary search tree being the value of the ordinate of each point in the set, and traversing the nodes in the balanced binary search tree; step 4: whenever traversing one node, computing whether sightline corresponding to the node is blocked, and recording an attribute of whether sightline corresponding to the node is blocked in a list; if sightline corresponding to the node is not blocked, continuing to traverse the left subtree thereof, and defining sightline corresponding to the node and all points on the right subtree 6102117 the node as being unblocked, if sightline corresponding to the node is not blocked, defining sightline corresponding to the node and all points on the left subtree of the node as being unblocked, and computing whether sightline corresponding to the right sub-node of the node is blocked: if sightline corresponding to the right sub-node of the node is not blocked, defining sightline corresponding to the remaining unmarked nodes as being unblocked, and stopping the traversal; if sightline corresponding to the right sub-node of the node has been blocked, continuing to traverse the right subtree thereof; in the process of traversing the nodes, if encountering one node that has been marked whether the corresponding line of sight is blocked, directly reading a result of whether its corresponding line of sight is blocked from the list, and stopping the traversal when whether the sight lines corresponding to all nodes are blocked is marked; step 5: retrieving points with an abscissa of k in the point set {N (xy, v1), No(x2, V2), +++, N5(Xs, Ys)}, wherein, 0 < k < m,recording the subset comprised of the retrieved points as {N, (k, y1), ++, N,(k, Vmax) wherein, j is the total number of points with the abscissa of k, point with the largest ordinate is recorded as Nkmax» and Vimaxls a value of the ordinate of Nkmax- Determining whether sightline Lxmax corresponding to the point Nkmax 18 blocked.

If sightline Lemax1S blocked, recording sightline corresponding to all points with the abscissa of k in the point set {N, (xq, Y1), N7(*2, yo), , N5(X5, Ys)} as being blocked.

If sightline Limax18 not blocked, establishing a balanced binary search tree with points in the set {N,(k y,), ‚N;(k, Vimax)}, the value of each node in the balanced binary search tree being the value of the ordinate of each point in the set, and traversing the nodes in the balanced binary search tree, going to step 4. step 6: taking k = 1,k = 2, ---,k = m respectively and repeating the step 5 to complete the computation of whether all sightlines L,, La, +, L, are blocked.

Further, in step (6), a method for outputting the mountain view visible area data and imaging to generate the mountain view visible area map specifically comprises: LU102117 (6.1) computing a numerical value of the mountain view visible area For a line of light L;e{L,, Ly, ---, Ls}, if Li; is marked as being blocked, assigning an attribute value pu; = 0 to L;, and if L; is marked as being unblocked, assigning an attribute value u; =1 to Lj.

That is, color of the grid corresponding to the observation point is set according to the MVF value, the larger the MVF value, the darker color, the smaller the MVF value, the lighter color. (6.3) generating the mountain view visible area map The observation area model rich in MVF value color attributes is re-placed into the overall database scene, that is, colored grid is placed in the position corresponding to the original model.

Preferably, this patent can supplement atmospheric visibility constraints.

In addition, the present invention further provides a system for measuring a mountain view visible area in a city, the system comprising the following modules: an integral scene construction module, collecting and constructing a real three-dimensional model scene comprising a mountain and a city area; an observation area full-surface rasterization module, extracting an observation area and rasterizing a model surface; LU102117 an observation point spherical coordinate system creation module, setting an observation point and creating a spherical coordinate system according to a boundary of the visual field; a mountain effective projection plane cutting module, cutting out a mountain effective projection plane in the spherical coordinate system; a mountain view sight blocking computation module, generating a mountain view sightline, and computing whether sightline is blocked, a mountain view sight blocking computation module, generating a mountain view sightline, and computing whether sightline is blocked.

Further, the specific functions of the integral scene construction module are as follows: (1.1) acquiring oblique photography data comprising the mountain and the city area through actual measurement; (1.2) generating, according to the acquired oblique photography data, a real three- dimensional model based on real image texture, (1.3) loading the real three-dimensional model acquired from the oblique photography data through a SuperMap platform.

Further, the specific functions of the observation area full-surface rasterization module are as follows: (2.1) extracting the observation area, extracting the observation area from the real three- dimensional model obtained by loading oblique photography on the SuperMap platform to observe the mountain; (2.2) rasterizing an entire surface of the observation area in the real three-dimensional model.

Further, the specific functions of the observation point spherical coordinate system creation module are as follows: (3.1) setting coordinates of the observation point, and selecting a geometric center point of each grid as an observation point representing the grid; (3.2) creating the spherical coordinate system to convert an observer in city space into the observation point in three-dimensional space O(xo; Vo: Zo), that is a grid observation point,

wherein (xo, Yo) is a value of a plane coordinate where the observer is located, and z, isl&J102117 horizontal plane height of the observation point; taking the horizontal plane V, at the height of the observation point as a plane, and taking a maximum visible distance Rymax in a current environment as a radius to make a visible hemisphere, and defining the hemisphere as a standard projection plane P,; taking the observation point O(x,,V,,Z,) as a sphere center, and separately taking a due north direction in a geographic coordinate system and a vertical direction of the horizontal plane V, as vector bases to establish the spherical coordinate system (r,0,@); (3.3) recording angle values a, and B, between the boundary of the visual field of the observation point and the vector bases in the due north direction of the spherical coordinate system.

Further, the specific functions of the mountain effective projection plane cutting module are as follow: in the spherical coordinate system, making a projection P, of the mountain on the horizontal plane V,, taking the point with the largest distance from the observation point in the projection P, and recording coordinates of the point as (r,, 0, 9; ), wherein meanwhile, 7; is a distance from the point to the observation point,p; 1s an angle between a line connecting the point and the observation point and a coordinate axis in the due north direction, taking an angle bisector of the boundary of the visual field of the observation point on the horizontal plane V,, the angle bisector intersecting a standard projection plane Pat a point (Romax» 0,0.5(a, + Bo), if Te > Rymax, making a planeP, tangent to the standard projection plane P, in a mode of passing through the point (Rymax 0,0.5(a, + Bo)), then P,is an approximate projection plane; if 1 < Rymaxtaking the horizontal plane V, at the height of the observation point as the plane and takingr;as a radius to make a reference hemisphere C,, and then passing through the point (7, 0,@;) to make a plane P tangent to the reference hemisphere C,, then P, is the approximate projection plane; on the approximate projection plane P,, making straight lines perpendicular to the horizontal plane V, in a mode of separately passing through (min(Rymax Te), 0, a5) and (min(Rymax Te), 0, Bo), wherein an area where the approximate projection plane P, is cut out by two straight lines is an approximate effective projection aré4J102117 Pa; for the area at 2/3 or more of a height of the mountain, making its projection on the approximate effective projection area P,,, wherein the projection is an approximate effective mountain projection.

Further, the specific functions of the mountain view sight blocking computation module are as follows: (5.1) rasterizing the effective mountain projection in m X n rectangular grid areas, taking a grid center point in a lower left corner as an origin, establishing an orthogonal coordinate system Ç on the approximate effective projection area P,a, and simplifying the rasterized effective mountain projection into a point set {N,(x,, yi), No(x2, yo), , No(xs, Vs) } composed of the center points of these grids, wherein, (xq, V1), (x3, V2), =, (xs, Vs) is the discrete coordinates of the points in a two-dimensional orthogonal coordinate system Ç after the mountain projection being rasterized into the point set,0 < x; <m, 0<y; <n, 1<i< S,S is the total number of center points of the grids, the connecting line from the observation point O to the point Ny, N,, ---, N; being recorded as sightline L4,L,,-, Lg, the center point of each grid having a weight w;, wherein, 0 < w; < 1; (5.2)Computing the sightline blocking step 1: retrieving the point with an abscissa of O in the point set {N (xq, v1), No(x2, V2), +++, N5(Xs, Ys)}, and recording the subset composed of the retrieved points as {N,(0, yi), +, N;(0, Vomax)} wherein j is the total number of points with the abscissa of 0, and the point with the largest ordinate at the abscissa of 0 is recorded as Nomax>Yomax 18 the value of the ordinate of Nomax; step 2: determining whether sightline Lomax corresponding to the point Nomax 1S blocked, if sightline Lomax 1S blocked,then sightline corresponding to all the points with the abscissa of O in the point set {N,(x,, v1), N,(x2, V2), =, Ns(Xxs, ys)} is recorded as being blocked; if sightline Lomax 1S not blocked, going to step 3; step 3: establishing a balanced binary search tree with points in the set {N1(0,¥,), =, N;(0, Vomax)}, the value of each node in the balanced binary search tree being the value of the ordinate of each point in the set, and traversing the nodes in the balanced binary search tree; LU102117 step 4: whenever traversing one node, computing whether sightline corresponding to the node is blocked, and recording an attribute of whether sightline corresponding to the node is blocked in a list;

if sightline corresponding to the node is not blocked, continuing to traverse the left subtree thereof, and defining sightline corresponding to the node and all points on the right subtree of the node as being unblocked,

if sightline corresponding to the node is not blocked, defining sightline corresponding to the node and all points on the left subtree of the node as being unblocked, and computing whether sightline corresponding to the right sub-node of the node is blocked:

if sightline corresponding to the right sub-node of the node is not blocked, defining sightline corresponding to the remaining unmarked nodes as being unblocked, and stopping the traversal;

if sightline corresponding to the right sub-node of the node has been blocked, continuing to traverse the right subtree thereof;

in the process of traversing the nodes, if encountering one node that has been marked whether the corresponding line of sight is blocked, directly reading a result of whether its corresponding line of sight is blocked from the list, and stopping the traversal when whether the sight lines corresponding to all nodes are blocked is marked,

step 5: retrieving points with an abscissa of k in the point set {N (xq, v1), No(x2, V2), +++, N5(X5, Ys)}, wherein, 0 < kK < m, recording the subset composed of the retrieved points as {N;(k yy), =, N;(k, Vimax)}, wherein, j is the total number of points with the abscissa of k, point with the largest ordinate is recorded as Nymax, and Yımax 1S a value of the ordinate of Nrmax; determining whether sightline Lemax corresponding to the point Nkmax 18 blocked, if sightlinely, «1s blocked, recording sightline corresponding to all points with the abscissa of k in the point set {N, (xq, V1), N7(*2, yo), , Ng(xs, Ys)} as being blocked; if sightline Limax18 not blocked, establishing a balanced binary search tree with points in the set {N;(k, y1), *, N;(K, Vkmax)}, the value of each node in the balanced binary search tree being the value of the ordinate of each point in the set, and traversing the nodes in the balanced binary search tree, going to step 4. LU102117 step 6, taking k = 1,k = 2,---, k = m respectively and repeating the step 5 to complete the computation of whether all sightlines L,, La, +, L, are blocked.

Further, the specific functions of the data output and imaging module are as follows: (6.1) computing a numerical value of the mountain view visible area, wherein for the line of light Lie{L,, Ly, ---, Ls}, if Li is marked as being blocked, assigning an attribute value |; = 0 to Lj, and if L; is marked as being unblocked, assigning an attribute value jy = 1 to Lj; defining a MVF value, MVF = marais the value range of MVF is [0,1], which represents a mountain view visible rate of the observer at a certain observation point under certain atmospheric visibility constraints; (6.2) imaging via color, setting a point on a three-dimensional map as an observation point, computing a value of the mountain view visible rate in real time by inputting a maximum visible distance and an observer's visual field angle range , and setting color of the grids corresponding to the observation points according to the MVF value; (6.3) generating the mountain view visible area map, that is placing colored grid into a corresponding position in an original model.

Claims

Claims: LU102117

1. A method for measuring a mountain view visible area in a city, comprising the following steps: (1) collecting and constructing a real three-dimensional model scene comprising a mountain and a city area; (2) extracting an observation area and rasterizing a model surface; (3) setting an observation point and creating a spherical coordinate system according to a boundary of a visual field, (4) cutting out a mountain effective projection plane in the spherical coordinate system; (5) generating a mountain view sightline, and computing whether the sightline is blocked, and (6) outputting mountain view visible area data and imaging to generate a mountain view visible area map.

2. The method for measuring the mountain view visible area in the city according to claim 1, wherein in step (1), a method for collecting and constructing the real three-dimensional model scene comprising the mountain and the city area comprises: (1.1) acquiring oblique photography data comprising the mountain and the city area through actual measurement; (1.2) generating, according to the acquired oblique photography data, a real three- dimensional model based on real image texture; and (1.3) loading the real three-dimensional model acquired from the oblique photography data through a SuperMap platform.

3. The high-precision method for measuring the mountain view visible area in the city according to claim 1 or 2, wherein in step (2), a method for extracting the observation area and rasterizing a model surface comprises: (2.1) extracting the observation area from the real three-dimensional model; and (2.2) rasterizing an entire surface of the observation area in the real three-dimensional model.

4. The method for measuring the mountain view visible area in the city according to claim

3, wherein in step (3), a method for setting the observation point and creating the sphericaU102117 coordinate system according to a sightline angle comprises: (3.1) setting coordinates of the observation point, and selecting a geometric center point of each grid as an observation point representing the grid; (3.2) creating the spherical coordinate system to convert an observer in city space into the observation point in three-dimensional space O(x,,¥,,Z,), that is a grid observation point, wherein (xo, Yo) is a value of a plane coordinate where the observer is located, and z, is a horizontal plane height of the observation point; taking a horizontal plane at the height of the observation point V, as a plane, and taking a maximum visible distance in a current environment Rumax as a radius to make a visible hemisphere, and defining the hemisphere as a standard projection plane P,; and taking the observation point O(x,,¥,,Z,) as a sphere center, and separately taking a due north direction in a geographic coordinate system and a vertical direction of the horizontal plane V, as vector bases to establish the spherical coordinate system (r, 0, @); (3.3) recording angle values a, and B, between the boundary of the visual field of the observation point and the vector bases in the due north direction of the spherical coordinate system.

5. The method for measuring the mountain view visible area in the city according to claim 4, wherein in step (4), a method for cutting out the mountain effective projection plane in the spherical coordinate system comprises: in the spherical coordinate system, making a projection P, of the mountain on the horizontal plane V,, taking a point with the largest distance from the observation point in the projection P, and recording coordinates of the point as (r,, 0, 9; ), wherein meanwhile, 7; is a distance from the point to the observation point, @; is an angle between a line connecting the point and the observation point and a coordinate axis in the due north direction, taking an angle bisector of the boundary of the visual field of the observation point on the horizontal plane V, , the angle bisector intersecting the standard projection plane P, at a point (Rymax 0, 0.5(% + Bo)), and if 7; > Rymax, making a plane P, tangent to the standard projection plane P, in a mode of passing through the point (Rymax 0,0.5(a, + Bo)), wherein

P,is an approximate projection plane; if r, < Rymax» taking the horizontal plane V at th&J102117 height of the observation point as the plane and taking 7, as a radius to make a reference hemisphere C,, then making a plane P,tangent to the reference hemisphere C,, wherein P, is the approximate projection plane; on the approximate projection plane P,, and making straight lines perpendicular to the horizontal plane V, in a mode of separately passing through (min(Rymax Te), 0, @,) and (min(Rymax Te), 0, Bo), wherein an area where the approximate projection plane P, is cut out by the two straight lines is an approximate effective projection area P,a; and for an area at 2/3 or more of a height of the mountain, making its projection on the approximate effective projection area P,,, wherein the projection is an approximate effective mountain projection.

6. The method for measuring the mountain view visible area in the city according to claim 5, wherein in step (5), a specific method for generating the sightline for the mountain view, and computing whether the sightline is blocked comprises: (5.1) generating the mountain view sightline, rasterizing the effective mountain projection in m Xn rectangular grid areas, taking a grid center point in a lower left corner as an origin, establishing an orthogonal coordinate system Ç on the approximate effective projection area Pa , and simplifying the rasterized effective mountain projection into a point set {N (xy, v1), No(x2, V2), +++, N(x, Ys)} composed of center points of these grids, wherein (x1, V1), (x3, V3), ==, (x5, V5) is discrete coordinates of the points in a two-dimensional orthogonal coordinate system Ç after the mountain projection is rasterized into the point set,0 < x; < m, O0 < y; < n,1 <i <S, Sis the total number of the center points of the grids, connecting lines from the observation point O to points Nj, N,,---, N; are recorded as the sightlines L,, Lz, ++, Lg, and a center point of each grid has a weight w;, wherein0 < W; < 1; (5.2) computing the sightline blocking step 1, retrieving points with an abscissa of O in the point set {N (xq, v1), No (x0, V2), +++, N(x, Ys)}, and recording a subset composed of the retrieved points as {N,(0,y1),-—, N;(0, Vomax)}, Wherein j is the total number of the points with the abscissa of 0, a point with the largest ordinate and the abscissa of 0 is recorded as Nomax» and Yomax is a value of the ordinate of Ny ax:

step 2, determining whether a sightline Lomax corresponding to the point Nomax 184102117 blocked, if the sightline Lomax 1S blocked, recording sightlines corresponding to all the points with the abscissa of 0 in the point set {N; (xy, V1), N2(x>, yo), , N5(Xs, Ys)} as being blocked, and if the sightline Lomax 1s not blocked, going to step 3;

step 3, establishing a balanced binary search tree with the points in the set {N (0, y1), -—- ,N;(0, Vomax)}, à value of each node in the balanced binary search tree being a value of an ordinate of each point in the set, and traversing the nodes in the balanced binary search tree:

step 4, whenever traversing one node, computing whether a sightline corresponding to the node is blocked, and recording an attribute of whether the sightline corresponding to the node is blocked in a list;

if the sightline corresponding to the node is not blocked, continuing to traverse a left subtree thereof, and defining sightlines corresponding to the node and all points on a right subtree of the node as being unblocked;

if the sightline corresponding to the node has been blocked, defining sightlines corresponding to the node and all points on the left subtree of the node as being unblocked, and computing whether a sightline corresponding to a right sub-node of the node is blocked:

if the sightline corresponding to the right sub-node of the node is not blocked, defining sightlines corresponding to the remaining unmarked nodes as being unblocked, and stopping the traversal,

if the sightline corresponding to the right sub-node of the node has been blocked, continuing to traverse the right subtree thereof; and in the process of traversing the nodes, if encountering one node that has been marked whether the corresponding sightline is blocked, directly reading a result of whether its corresponding sightline is blocked from the list, and stopping the traversal when whether the sightlines corresponding to all nodes are blocked is marked;

step 5, retrieving points with an abscissa of k in the point set EN, (xq, v1), No(x2, V2), +++, N5(X5, Ys)}, wherein 0 < kK < m, recording a subset composed of the retrieved points as {Ny (k y1), +, N;(K, Yımax)}, Wherein, j is the total number of the points with the abscissa of k, a point with the largest ordinate is recorded as Nimax, and Yimax1LdJ102117 value of the ordinate of the Nkmax; determining whether a sightline Ly, corresponding to the point Nkmax 18 blocked, and if the sightline Limax is blocked, recording sightlines corresponding to all the points with the abscissa of k in the point set {N,(x1,V1), N2(X2, V2), ++, N5(Xs, ys)} as being blocked; and if the sightline Limax is not blocked, establishing a balanced binary search tree with the points in the set {N,(k, yi), Ni(K, Viemax) } a value of each node in the balanced binary search tree being a value of an ordinate of each point in the set, traversing the nodes in the balanced binary search tree, and going to step 4; step 6, taking k = 1,k = 2,---, k = m respectively and repeating step 5 to complete the computation of whether all sightlines L,, L,, ++, L, are blocked.

7. The method for measuring the mountain view visible area in the city according to claim 6, wherein in step (6), a specific method for outputting the mountain view visible area data and imaging to generate the mountain view visible area map comprises: (6.1) computing a numerical value of the mountain view visible area, wherein for a sightline Lje{L,, L2, ---, Lg}, if L; is marked as being blocked, assigning an attribute value Ww; = Oto Lj, and if L; is marked as being unblocked, assigning an attribute value u; = 1 to L;; and defining a MVF value, MVF = ee] wherein a value range of MVF is [0,1], which represents a mountain view visible rate of an observer at a certain observation point under certain atmospheric visibility constraints; (6.2) imaging via color, setting a point on a three-dimensional map as an observation point, computing a value of the mountain view visible rate in real time by inputting a maximum visible distance and an observer's visual field angle range, and setting color of the grid corresponding to the observation point according to the MVF value; and (6.3) generating the mountain view visible area map, that is placing colored grid into a corresponding position in an original model.

8. A system for measuring a mountain view visible area in a city, comprising the following modules: an integral scene construction module, collecting and constructing a real three-dimensional model scene comprising a mountain and a city area; LU102117 an observation area full-surface rasterization module, extracting an observation area and rasterizing a model surface; an observation point spherical coordinate system creation module, setting an observation point and creating a spherical coordinate system according to a boundary of a visual field, a mountain effective projection plane cutting module, cutting out a mountain effective projection plane in the spherical coordinate system; a mountain view sightline blocking computation module, generating a mountain view sightline, and computing whether the sightline is blocked; and a data output and imaging module, outputting mountain view visible area data and imaging to generate a mountain view visible area map.

9. The system for measuring the mountain view visible area in the city according to claim 8, wherein specific functions of the integral scene construction module are as follows: (1.1) acquiring oblique photography data comprising the mountain and the city area through actual measurement, (1.2) generating, according to the acquired oblique photography data, a real three- dimensional model based on real image texture; and (1.3) loading the real three-dimensional model acquired from the oblique photography data through a SuperMap platform.

10. The system for measuring the mountain view visible area in the city according to claim 8 or 9, wherein specific functions of the observation area full-surface rasterization module are as follows: (2.1) extracting the observation area from the real three-dimensional model; and (2.2) rasterizing an entire surface of the observation area in the real three-dimensional model.

11. The system for measuring the mountain view visible area in the city according to claim 10, wherein specific functions of the observation point spherical coordinate system creation module are as follows: (3.1) setting coordinates of the observation point, and selecting a geometric center point of each grid as an observation point representing the grid; LU102117 (3.2) creating the spherical coordinate system to convert an observer in city space into the observation point in three-dimensional space O(xo; Vo: Zo), that is a grid observation point, wherein (xo, Yo) is a value of a plane coordinate where the observer is located, and z, is a horizontal plane height of the observation point; taking a horizontal plane V, at the height of the observation point as a plane, and taking a maximum visible distance Rymax in a current environment as a radius to make a visible hemisphere, and defining the hemisphere as a standard projection plane P,; taking the observation point O(xo,Yo:Zo) as a sphere center, and separately taking a due north direction in a geographic coordinate system and a vertical direction ofthe horizontal plane V, as vector bases to establish the spherical coordinate system (r,0,@); (3.3) recording angle values a, and B, between the boundary of the visual field of the observation point and the vector bases in the due north direction of the spherical coordinate system.

12. The system for measuring the mountain view visible area in the city according to claim 11, wherein specific functions of the mountain effective projection plane cutting module are as follows: in the spherical coordinate system, making a projection P, of the mountain on the horizontal plane V,, taking a point with the largest distance from the observation point in the projection P, and recording coordinates of the point as (7, 0, 9;), wherein meanwhile, 7; is a distance from the point to the observation point, @; is an angle between a line connecting the point and the observation point and a coordinate axis in the due north direction, taking an angle bisector of the boundary of the visual field of the observation point on the horizontal plane V, , the angle bisector intersecting the standard projection plane P, at a point (Romax» 0,0.5(a, + Bo), and if 1, > Rymax, making a plane P, tangent to the standard projection plane P, in a mode of passing through the point (Rymax 0,0.5(a, + Bo)), wherein P,is an approximate projection plane; if r, < Rymax» taking the horizontal plane V, at the height of the observation point as the plane and taking 7, as a radius to make a reference hemisphere C,, then making passing through the point (1, 0,¢.), wherein P, is the approximate projection plane; on the approximate projection plane P,, making straight link$J102117 perpendicular to the horizontal plane V, in a mode of separately passing through (min(Rymax Te), 0, a5) and (min(Rymax Te), 0, Bo), wherein an area where the approximate projection plane P, is cut out by the two straight lines is an approximate effective projection area Pa; and for the area at 2/3 or more of a height of the mountain, making its projection on the approximate effective projection area FP,,, wherein the projection is an approximate effective mountain projection.

13. The system for measuring the mountain view visible area in the city according to claim 12, wherein specific functions of the mountain view sightline blocking computation module are as follows: (5.1) generating the sightline for the mountain view, rasterizing the effective mountain projection in m X n rectangular grid areas, taking a grid center point in a lower left corner as an origin, establishing an orthogonal coordinate system Ç on the approximate effective projection area P,,, and simplifying the rasterized effective mountain projection into a point set {N;(xq, v1), N,(*2, V2), ++, Ng(xs, Ys)} composed of center points of these grids, wherein(x,, v1), (x2, V2), ++, (x5, Vs) is discrete coordinates of the points in a two-dimensional orthogonal coordinate system Ç after the mountain projection is rasterized into the point set,0 < x; < m, O0 < y; < n,1 <i <S, Sis the total number of the center points of the grids, connecting lines from the observation point O to points N,, N,,‘-, N; are recorded as — sightlines L,, L», ++, Lg, and a center point of each grid has a weight w;, wherein, 0 < w; < 1; (5.2) Computing the sightline blocking step 1, retrieving points with an abscissa of O in the point set {N (xq, v1), No(x2, V2), +++, N5(Xs5, Ys)}, and recording a subset composed of the retrieved points as {N,(0, yi), +, N;(0, Yomax) }» wherein j is the total number of the points with the abscissa of 0, and a point with the largest ordinate and the abscissa of 0 is recorded as Nomax, and Yomax is the value of the ordinate of Nomax: step 2, determining whether a sightline Lomax corresponding to the point Nomax 1S blocked, if the sightline Lomax 1S blocked, recording sightlines corresponding to all the points with the abscissa of 0 in the point set {N; (xy, V1), N2(x>, yo), , N5(Xs, Ys)} as being blocked,

and if the sightline Lomax 1s not blocked, going to step 3; LU102117 step 3: establishing a balanced binary search tree with the points in the set {N,(0, yi), +, N;(0, Vomax)} a value of each node in the balanced binary search tree being a value of an ordinate of each point in the set, and traversing the nodes in the balanced binary search tree; step 4, whenever traversing one node, computing whether a sightline corresponding to the node is blocked, and recording an attribute of whether the sightline corresponding to the node is blocked in a list; if the sightline corresponding to the node is not blocked, continuing to traverse a left subtree thereof, and defining sightlines corresponding to the node and all points on a right subtree of the node as being unblocked;

if the sightline corresponding to the right sub-node of the node is not blocked, defining sightlines corresponding to the remaining unmarked nodes as being unblocked, and stopping the traversal;

if the sightline corresponding to the right sub-node of the node has been blocked, continuing to traverse the right subtree thereof; and in the process of traversing the nodes, if encountering one node that has been marked whether the corresponding sightline is blocked, directly reading a result of whether its corresponding sightline is blocked from the list, and stopping the traversal when whether the sight lines corresponding to all nodes are blocked is marked;

step 5, retrieving points with an abscissa of k in the point set

{N;(Cxq, v1), N2(*2, v2), +++, N5(X5, Ys)}, wherein 0 < kK < m, recording a subset composed of the retrieved points as {N,(k, y,), =, N;(k, Vimax)}, wherein, j is the total number of the points with the abscissa of k, a point with the largest ordinate is recorded as Nymax, and Yımaxls a value of the ordinate of Nkmax; determining whether a sightline Lxmax corresponding to the point Nkmax 18 blocked, and if the sightline Limax is blocked, recording sightlines corresponding to all the points with the abscissa of k in the point seU102117 {N (xq, v1), No(x2, V2), +++, N(x, Ys)} as being blocked; and if the sightline Limax1S not blocked, establishing a balanced binary search tree with the points in the set {N,& yp), N;(k, Vimax)}, à value of each node in the balanced binary search tree being a value of an ordinate of each point in the set, traversing the nodes in the balanced binary search tree, and going to step 4; step 6, taking k = 1,k = 2,---, k = m respectively and repeating step 5 to complete the computation of whether all sightlines L,, L,, ++, L, are blocked.

14. The system for measuring the mountain view visible area in the city according to claim 13, wherein specific functions of the data output and imaging module are as follows: (6.1) computing a numerical value of the mountain view visible area, wherein for a sightline Lje{L,, L2, ---, Lg}, if L; is marked as being blocked, assigning an attribute value H; = Oto Li, and if L; is marked as being unblocked, assigning an attribute value pu; = 1 to L;; and defining a MVF value, MVF = ee] wherein a value range of MVF is [0,1], which represents a mountain view visible rate of the observer at a certain observation point under certain atmospheric visibility constraints; (6.2) imaging via color, setting a point on a three-dimensional map as an observation point, computing a value of the mountain view visible rate in real time by inputting a maximum visible distance and an observer's visual field angle range, and setting color of the grid corresponding tothe observation point according to the MVF value; and (6.3) generating the mountain view visible area map, that is placing colored grid into the corresponding position in an original model.