CN117036647A - Ground surface extraction method based on inclined live-action three-dimensional model - Google Patents
Ground surface extraction method based on inclined live-action three-dimensional model Download PDFInfo
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Abstract
The invention belongs to the technical field of mapping, and particularly relates to a ground curved surface extraction method based on an inclined live-action three-dimensional model. The method has higher and better adaptability and real feedback to the thinning and processing of the node data of the inclined live-action three-dimensional model.
Description
Technical Field
The invention belongs to the technical field of mapping, and particularly relates to a ground surface extraction method based on an inclined live-action three-dimensional model.
Background
The method is characterized in that the terrain data which can reflect the fluctuation of the ground terrain and does not contain the ground terrain is called a ground curved surface, is very important for planning and designing projects such as roads, bridges and hydraulic engineering, especially the mainstream engineering design software AutoDesk Civil 3D, and is more required to be used as a space data base for developing engineering design.
The existing ground surface extraction method mainly comprises a three-dimensional laser scanning ground surface extraction method, a satellite remote sensing data ground surface extraction method and a ground surface preparation method by manually collecting ground points. The prior art method has the following obvious defects:
1. the three-dimensional laser scanning technology has the problems of high cost and low utilization rate of product data. The three-dimensional laser scanning equipment purchasing, maintenance and data acquisition have the problem of overhigh cost, and the product data has narrower application range in the whole life cycle of engineering planning, design, construction and operation and maintenance, and has lower recycling rate;
2. the digital elevation model product manufactured by the satellite remote sensing data has the common problems of low precision, slow product updating period or high updating cost. The highest precision of the digital elevation model disclosed in the world at present is 12.5 meters, the timeliness of data is around 2009, elevation anomalies exist at a plurality of positions, professional personnel are required to specially correct the elevation anomalies so as to reflect rough terrain conditions to a certain extent, and the precision cannot meet engineering design requirements; if commercial satellites are adopted to specially collect the topographic data of the target area, the update period is uncertain, the collection cost is high, and the precision (meter level) still cannot meet the engineering design requirement;
3. the method for manufacturing the ground curved surface by manually collecting the ground points has the problems of high cost, low speed, limited timeliness and poor reducibility. The field collection process requires a lot of time and resources and may be limited in complex terrain and cannot fully and accurately restore the terrain conditions of various scales (such as valleys, ridges, depressions, ridges, ravines, channels, etc.) of the field.
The method is characterized in that four types of terrain feature parameters are linearly constructed into a multi-terrain feature complexity model, high-precision thinning of the point cloud is realized according to the acquired point cloud complexity and thinning criteria, the terrain is divided into regular grids with uniform resolution, the point cloud is vertically projected into corresponding grid units, each grid only holds one feature point, and the method is simple and quick, but can lose some detail information, especially thinning of incorrect ground cloud points extracted by noise points and suspended matters possibly occurring in the construction process of an inclined live-action three-dimensional model, so that the real ground condition cannot be effectively reflected.
Disclosure of Invention
Aiming at the problems of the known ground surface extraction method applied to the inclined live-action three-dimensional model, the invention provides a ground surface extraction method based on the inclined live-action three-dimensional model.
The ground surface extraction method based on the inclined live-action three-dimensional model comprises the steps of S1 inclined model suspended matter filtering, S2 inclined model vertex set extraction, S3 non-ground point filtering and S4 ground point thinning, wherein the step of S4 ground point thinning is implemented through the following steps:
s41, reading point cloud: reading the point cloud data into a corresponding memory container, and waiting for memory access and algorithm execution;
s42, extracting a point cloud bounding box: traversing the point cloud coordinates, judging and reserving the maximum and minimum X, Y coordinates, and constructing a minimum bounding box of the point cloud range;
s43, dividing a thinning grid: dividing the constructed minimum bounding box into square grid areas according to a preset threshold, wherein each square grid area contains four points which are not contained in the four cases, 1 point contained in the square grid area, 2 points contained in the square grid area, 3 points contained in the square grid area and more than 3 points contained in the square grid area;
s44, minimum deviation thinning of points in the square area: according to the four cases of the square grids divided in the S43, searching the minimum deviation point in each square grid area, namely:
when the square grid area does not contain points, ignoring the square grid;
when the square grid area contains 1 point, the point is the minimum deviation point T in the square grid area 0 ；
When the square grid area contains 2 points, the midpoint of the 2-point connecting line is the minimum deviation point T in the square grid area 0 ；
When the square grid area contains 3 or more points, the number of points is N, and the minimum deviation point T is obtained by the following method 0 ；
Find the maximum outer surrounding sphere O of all points first 1 The maximum grid point package sphere is called as a maximum grid point package sphere, the maximum grid point package sphere center reflects the overall distribution state of all points in the current grid, and the sphere center is a point p 1 (x 1 ,y 1 ,z 1 ) The method comprises the steps of carrying out a first treatment on the surface of the Finding the distance point p again 1 Nearest c×n points, c being the core coefficient and 0< c <1, find the largest outer sphere O of these points 2 The core lattice point wrapping sphere reflects the distribution state of all points of the core area in the current lattice, and the sphere center is point p 2 (x 2 ,y 2 ,z 2 ) The method comprises the steps of carrying out a first treatment on the surface of the P is respectively 1 (x 1 ,y 1 ,z 1 )、p 2 (x 2 ,y 2 ,z 2 ) Adding a maximum weight m and a core weight n to the three-dimensional coordinates of the points, and calculating a minimum deviation point T with a weighting value according to the following formula 0 (x 0 ,y 0 ,z 0 )：
m + n = 1；
x 0 =m*x 1 +n*x 2 ；
y 0 =m*y 1 +n*y 2 ；
z 0 =m*z 1 +n*z 2 ；
Obtaining the minimum deviation point T 0 The algorithm of (1) is positioned as a double-wrapping weighted sphere center thinning method;
s45, performing point cloud thinning: performing point cloud judgment and thinning operation on each square area according to an S44 method, wherein each square area only keeps one nearest terrain characteristic point at most; after the thinning of all the square areas is completed, the rest point clouds form the needed characteristic point cloud closest to the terrain.
Furthermore, the non-ground point filtering adopts a CSF filtering algorithm, namely a ground point set in the vertex set data can be extracted, and the ground point set forms a data base of the required ground curved surface achievement.
The ground surface extraction method based on the inclined live-action three-dimensional model aims at realizing high-precision ground surface extraction available in engineering planning, design, construction and operation and maintenance full life cycle, and has the beneficial effects that:
1) Aiming at the problems of high cost and low utilization rate of product data in the three-dimensional laser scanning technology. According to the method provided by the invention, the equipment purchase, maintenance and data acquisition costs of the adopted inclined live-action three-dimensional model are low, the inclined live-action three-dimensional model can play an important role in the whole life cycle of engineering planning, design, construction and operation and maintenance, and the data utilization rate is high. Additionally, more and more existing inclined live-action three-dimensional models can be directly used, so that unnecessary cost expenditure and time consumption are avoided;
2) Aiming at the problems of low precision, slow product updating period or high updating cost of a digital elevation model product manufactured by satellite remote sensing data, the method provided by the invention has the advantages that the ground curved surface precision generated by the method is high (the cm-level precision consistent with the inclined live-action three-dimensional model) and meets the use of the engineering full life cycle, and the product updating difficulty is low, the period is short and the updating cost is low;
3) Aiming at the problems of high cost, low speed, limited timeliness and poor reducibility in the method for manufacturing the ground curved surface by manually collecting ground points, the method provided by the invention can realize full-flow programming automatic processing, and the product can realize real feedback on the topography conditions under various scales;
4) Compared with other common point cloud thinning algorithms, the double-wrapping weighted sphere center thinning method provided by the invention has higher and better adaptability and real feedback on the thinning and processing of the node data of the inclined live-action three-dimensional model. The conventional method may be too simplified or too randomly select representative points in some scenarios, resulting in less than ideal retention of the ground surface. The method comprehensively considers the characteristics of the ground point cloud extracted from the three-dimensional model of the inclined live-action, adopts the method of dividing grids, calculating the number of dividing points, using original double-wrapping weighted sphere center weight balance maximum area and core area weight under the multi-point condition, and optimizes the algorithm of more fitting the problems of suspended matters, noise points and the like existing in the model due to different topography fluctuation existing in the three-dimensional model of the inclined live-action; meanwhile, after the point cloud is thinned, the requirement of the construction of the ground surface on the computational power of a computer is greatly reduced, and the timeliness of the construction of the ground surface is optimized.
Drawings
Fig. 1 is an S41 point cloud schematic.
Fig. 2 is a schematic diagram of an S42 point cloud outer enclosure frame.
Fig. 3 is a schematic diagram of the thinning grid of S43.
Fig. 4 is a schematic diagram of distribution of points in a single square grid at S43.
Fig. 5 is a schematic diagram of minimum deviation point values when the single square grid includes 1 point in S43.
Fig. 6 is a schematic diagram of minimum deviation point values when the single square grid includes 2 points in S43.
Fig. 7 is a schematic diagram of the value of the center point of the wrapped sphere when the single square grid of S43 contains 3 or more points.
Fig. 8 is a schematic diagram of calculating the minimum deviation point of the center of the wrapped sphere at S43.
Fig. 9 is a schematic view of reserving one closest topographical feature point for each square grid at S44.
Fig. 10 is a schematic view of S4 closest terrain feature point cloud.
Description of the embodiments
Example 1: the method is used for extracting the ground curve from the inclined live-action three-dimensional model of a certain actual engineering construction area, and the implementation area has the following characteristics:
the minimum bounding box size is 154 x 178 meters, and the area is about 27412 square meters;
the main content of the model is the comprehensive ground expression of the urban area, and 254624 ground points are extracted from the key point set;
the engineering construction type is civil building planning design;
according to the requirements of mapping tasks, the accuracy requirement of a ground curved surface is required to be 0.5 meter;
the overall ground relief of the model is small, small-range topography factors such as a bank slope, a roadbed, a canal and the like exist on the ground, and large-range topography factors such as hills, basins, river banks and the like do not exist;
the suspended matters and noise points in the model are fewer, and the disturbance to the topography is smaller.
According to the above situation, the following definitions are provided:
according to engineering mapping task requirements, defining a thinning grid division length G=0.4 meter so as to ensure the required 0.5 meter precision requirement;
according to the area of an implementation area (27412 square meters) and the number of extracted ground points (254624), the number of average points in each square meter is calculated to be 9.29, and the number of average points in the range of 0.4 meter x 0.4 meter is calculated to be 3.71, so that the core coefficient c=0.55 of the core lattice point wrapping ball is defined, and in this implementation, the largest outer wrapping ball of the 2 points closest to the largest lattice point wrapping ball is called a core lattice point wrapping ball, and the ball center is called a core lattice point wrapping ball;
judging a minimum deviation point T in the process of thinning the ground point set according to the characteristics of small overall ground relief of the model, more ground small-range topography factors, few suspended matters and noise points on the model and the like 0 The method is characterized in that the distribution condition of all points in the current grid is focused, so that the maximum weight is defined as m=0.8, the core weight is defined as n=0.2, a double-package weighted sphere center thinning method is applied, and the ground point thinning is carried out on the model according to the following formula:
x 0 =0.8*x 1 + 0.2*x 2 ；
y 0 =0.8*y 1 + 0.2*y 2 ；
z 0 =0.8*z 1 + 0.2*z 2。
and according to the rules, constructing the ground surface in the AutoCAD Civil 3D, and finally directly extracting the ground surface by using key points in the inclined live-action three-dimensional model of all the implementation areas.
Claims (2)
1. The ground surface extraction method based on the inclined live-action three-dimensional model is characterized by comprising the steps of S1 inclined model suspended matter filtering, S2 inclined model vertex set extraction, S3 non-ground point filtering and S4 ground point thinning, wherein the step of S4 ground point thinning is implemented through the following steps:
s41, reading point cloud: reading the point cloud data into a corresponding memory container, and waiting for memory access and algorithm execution;
s42, extracting a point cloud bounding box: traversing the point cloud coordinates, judging and reserving the maximum and minimum X, Y coordinates, and constructing a minimum bounding box of the point cloud range;
s43, dividing a thinning grid: dividing the constructed minimum bounding box into square grid areas according to a preset threshold, wherein each square grid area contains four points which are not contained in the four cases, 1 point contained in the square grid area, 2 points contained in the square grid area, 3 points contained in the square grid area and more than 3 points contained in the square grid area;
s44, minimum deviation thinning of points in the square area: according to the four cases of the square grids divided in the S43, searching the minimum deviation point in each square grid area, namely:
when the square grid area does not contain points, ignoring the square grid;
when the square grid area contains 1 point, the point is the minimum deviation point T in the square grid area 0 ；
When the square grid area contains 2 points, the midpoint of the 2-point connecting line is the minimum deviation point T in the square grid area 0 ；
When 3 or more points are included in the square grid area, the number of points is N, and the most points are obtained as followsSmall deviation point T 0 ；
Find the maximum outer surrounding sphere O of all points first 1 Called maximum grid point package ball, its centre is point p 1 (x 1 ,y 1 ,z 1 ) The method comprises the steps of carrying out a first treatment on the surface of the Finding the distance point p again 1 Nearest c×n points, c being the core coefficient and 0< c <1, find the largest outer sphere O of these points 2 The sphere center is point p 2 (x 2 ,y 2 ,z 2 ) The method comprises the steps of carrying out a first treatment on the surface of the P is respectively 1 (x 1 ,y 1 ,z 1 )、p 2 (x 2 ,y 2 ,z 2 ) Adding a maximum weight m and a core weight n to the three-dimensional coordinates of the points, and calculating a minimum deviation point T with a weighting value according to the following formula 0 (x 0 ,y 0 ,z 0 )：
m + n = 1；
x 0 =m*x 1 +n*x 2 ；
y 0 =m*y 1 +n*y 2 ；
z 0 =m*z 1 +n*z 2 ；
S45, performing point cloud thinning: performing point cloud judgment and thinning operation on each square area according to an S44 method, wherein each square area only keeps one nearest terrain characteristic point at most; after the thinning of all the square areas is completed, the rest point clouds form the needed characteristic point cloud closest to the terrain.
2. The ground surface extraction method based on the inclined live-action three-dimensional model as claimed in claim 1, wherein the non-ground point filtering adopts a CSF filtering algorithm to extract a ground point set in the vertex set data, and the ground point set forms a data base of the required ground surface result.
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