CN112258570A

CN112258570A - Method and system for measuring and calculating water surface width of river full water area

Info

Publication number: CN112258570A
Application number: CN202011285535.XA
Authority: CN
Inventors: 陈曦; 崔要奎; 文长军; 杨天荣; 李欢; 罗增良; 姚照原
Original assignee: Aerospace Information Research Institute of CAS
Current assignee: Aerospace Information Research Institute of CAS
Priority date: 2020-11-17
Filing date: 2020-11-17
Publication date: 2021-01-22
Anticipated expiration: 2040-11-17
Also published as: CN112258570B

Abstract

The invention discloses a method and a system for measuring and calculating the water surface width of a river in a full water area. The method comprises the following steps: acquiring a riverway remote sensing image; determining a set formed by a plurality of straight lines of target points in a river channel remote sensing image as a target straight line set; determining a linear pixel point coordinate set of each straight line in a target straight line set based on a preset maximum detection river width threshold and a target point in a river channel; calculating the pixel coordinates of the left intersection point and the pixel coordinates of the right intersection point of all straight lines in the target straight line set based on the straight line pixel point coordinate set; calculating the pixel point distance between the pixel coordinate of any left intersection point and the pixel coordinate of any right intersection point corresponding to each straight line, and determining the minimum pixel point distance as the straight line distance between two banks of the corresponding straight line; and determining the minimum one of the linear distances between all the two banks as the river width of the target point in the river channel. The invention realizes the high-efficiency and high-precision measurement and calculation of large-range and dynamic river width.

Description

Method and system for measuring and calculating water surface width of river full water area

Technical Field

The invention relates to the field of remote sensing image analysis and photogrammetry, in particular to a method and a system for measuring and calculating the water surface width of a river in a full water area.

Background

The surface river water surface width (river width) is one of important hydrological parameters and is closely related to the surface runoff. The remote sensing data-based river width measurement and calculation of a large-scale and long-time sequence is beneficial to researching and mastering the change rule of the surface runoff, and has important significance for runoff monitoring, flood monitoring and other disaster monitoring in areas without data or with little data.

The measurement and calculation of the width of the surface river is always a hot point of remote sensing hydrology research. The commonly used definition of the river width on the ground surface is that a perpendicular line is made for the center line of the river channel, and the distance between the perpendicular line and the intersection point of the two banks is the river width of the current position. Based on this definition, there are currently several methods of estimation: the RivWidth tool extracts a River channel central line based on a Laplace convolution algorithm and calculates the width of the River channel, and a Global River width data set from Landsat (GRWL) of the Global main River width is constructed by adopting the method at present; the RivWidthCloud tool developed based on the Google Earth Engine (GEE) platform improves the problem that the central line of the river channel extracted by RivWidth is discontinuous, but the river width calculation method at the intersection of the river channel as well as RivWidth is invalid and is temporarily not suitable for remote sensing data beyond Landsat; RivaMap software developed based on a water body image singularity analysis method provides a river width calculation method based on a singularity index (singularity index), and river width calculation failure at river intersection also exists; the width of a large river in the world is extracted by using SRTM elevation data by adopting a method of the shortest distance from a central line to a river bank, but the method needs to remove influences of sandbars, islands and the like in the river channel, so that the width measurement and calculation of partial rivers such as a braided river are inaccurate.

The existing river width measuring and calculating method has the following problems: (1) the prior method depends on accurate extraction of the center line of the river channel when measuring and calculating the river width, and the extraction error of the center line of the river channel is transmitted to the river width measuring and calculating result, so that the uncertainty of the river width measuring and calculating is increased. For example, the existing river width measuring and calculating method cannot give complete and consistent definitions for the situations that the center lines of the river channels are not guidable, the center lines of multiple river channels intersect and the like, so that the measured value of the river width measuring and calculating result at the river channel turning or intersection is discontinuous; (2) when the river width is extracted by using multi-temporal remote sensing data, if the center line of the river channel deviates along with irregular expansion or contraction of the water surface, the position of the center line corresponding to the river width calculated by the existing method changes correspondingly, a river width measurement result of the water surface position except the center line of the river channel cannot be given, and consistency and comparability of the river width values measured at different periods cannot be guaranteed, so that the requirement of large-scale and dynamic river width measurement cannot be met, and an effective river width data set is still lacked.

In summary, the river width is calculated in the traditional method not by an independent problem but by accurate extraction of the center line of the river channel, and in order to simplify calculation, the existing method extracts the river width by neglecting the existence of river channel intersections or sand continents and islands, so that the river width cannot be accurately calculated. In addition, the river channel width often changes with the change of the runoff volume, and then the center line of the river channel may change, so that the calculation target point of the river width measurement cannot be kept consistent, and therefore, a method for measuring and calculating the water surface width of the whole river water area (namely, any point in the river channel) is lacked at present.

Disclosure of Invention

Therefore, a method and a system for measuring and calculating the water surface width of the whole river water area are needed to be provided, so that the defect of the traditional method for measuring and calculating the water surface width of the whole river water area is overcome, and the efficient and high-precision measurement and calculation of the dynamic river width in a large range are realized.

In order to achieve the purpose, the invention provides the following scheme:

a method for measuring and calculating the water surface width of a river in the whole water area comprises the following steps:

acquiring a riverway remote sensing image;

determining a river channel internal image and a river channel external image in the river channel remote sensing image;

determining a set formed by a plurality of straight lines passing through target points in the riverway remote sensing image as a target straight line set; setting linear inclination angle sampling interval values at intervals of the inclination angles of any two adjacent straight lines in the target straight line set; the inclination angle is an included angle between a straight line and a transverse axis of a rectangular coordinate system; the rectangular coordinate system is a coordinate system established by taking the target point in the river as the center of a circle, taking the east to the west as a horizontal axis and taking the south to the north as a longitudinal axis; the target point in the river channel is any one pixel point in the image in the river channel;

determining a linear pixel point coordinate set of each straight line in the target straight line set based on a preset maximum detection river width threshold and the target point in the river channel; the linear pixel point coordinate set is a coordinate set of pixels of which the straight lines pass through the riverway remote sensing image;

calculating the pixel coordinates of the left intersection point and the pixel coordinates of the right intersection point of all straight lines in the target straight line set based on the straight line pixel point coordinate set; the left intersection point is a pixel point which is formed by the intersection of a straight line and a river channel left bank positioned on one side of a target point in the river channel; the right intersection point is a pixel point of a straight line intersected with the right bank of the river channel positioned on the other side of the target point in the river channel;

calculating pixel point distance between the pixel coordinate of any one left intersection point and the pixel coordinate of any one right intersection point corresponding to each straight line, and determining the minimum pixel point distance as the straight line distance between two banks of the corresponding straight line;

and determining the minimum one of the linear distances between the two banks as the river width of the target point in the river channel remote sensing image.

Optionally, the determining, based on a preset maximum detected river width threshold and the target point in the river, a linear pixel point coordinate set of each line in the target linear set specifically includes:

when the angle of inclination of the straight line is equal to

Then, determining a linear pixel point coordinate set by a preset maximum detection river width threshold value and a row of pixels where target points in the river channel are located;

when the angle of inclination of the line is not equal to

And then, based on a preset maximum detection river width threshold value and the target points in the river channel, determining a linear pixel point coordinate set by adopting an indeterminate equation algorithm.

Optionally, the inclination angle of the straight line is not equal to

And then, based on a preset maximum detection river width threshold value and the target points in the river channel, determining a linear pixel point coordinate set by adopting an indeterminate equation algorithm, wherein the method specifically comprises the following steps:

selecting an abscissa according to the preset maximum detection river width threshold and the abscissa of the target point in the river channel at set intervals to obtain a first abscissa continuous integer sequence;

substituting the first abscissa continuous integer sequence into any linear equation expression of a target point in the river channel, and performing upward rounding operation on the obtained ordinate continuous integer sequence corresponding to the first abscissa continuous integer sequence to obtain a first ordinate continuous integer sequence; the first horizontal coordinate continuous integer sequence and the first vertical coordinate continuous integer sequence form a first pixel point coordinate sequence;

selecting vertical coordinates according to the preset maximum detection river width threshold value and the vertical coordinates of the target points in the river channel at set intervals to obtain a second vertical coordinate continuous integer sequence;

substituting the second continuous integer sequence of the ordinate into any linear equation expression of a target point in the river channel, and performing upward rounding operation on the obtained continuous integer sequence of the abscissa corresponding to the second continuous integer sequence of the ordinate to obtain a second continuous integer sequence of the abscissa; the second horizontal coordinate continuous integer sequence and the second vertical coordinate continuous integer sequence form a second pixel point coordinate sequence;

and determining the union set of the first pixel point coordinate sequence and the second pixel point coordinate sequence as a linear pixel point coordinate set.

Optionally, the calculating, based on the linear pixel point coordinate set, a pixel coordinate of a left intersection point and a pixel coordinate of a right intersection point of each straight line in the target linear set specifically includes:

determining a pixel coordinate set of a left bank of the river channel and a pixel coordinate set of a right bank of the river channel in the remote sensing image of the river channel;

calculating the intersection of the pixel coordinate set of the left bank of the river channel and the linear pixel point coordinate set to obtain a left bank intersection point coordinate;

calculating the intersection of the pixel coordinate set of the right bank of the river channel and the linear pixel point coordinate set to obtain right bank intersection point coordinates;

substituting any one left bank intersection point coordinate and any one right bank intersection point coordinate into an intersection point judgment formula; the intersection point judgment formula is less than EOF and greater than pi/2; wherein O represents a target point in the river; e represents a left bank intersection point; f represents a right bank intersection point; the angle EOF is an angle with O as a vertex and with OE and OF as two edges;

and determining the left bank intersection point coordinate meeting the intersection point judgment formula as the pixel coordinate of the left intersection point, and determining the right bank intersection point coordinate meeting the intersection point judgment formula as the pixel coordinate of the right intersection point.

Optionally, the calculating a pixel point distance between any one of the pixel coordinates of the left intersection point and any one of the pixel coordinates of the right intersection point corresponding to each straight line specifically includes:

wherein, | EF_θ| is the pixel coordinate (x) of the left intersection_Eθ′,y_Eθ') pixel coordinate (x) of right intersection point_Fθ′,y_Fθ') pixel distance between.

Optionally, after determining the minimum one of the linear distances between all the two banks as the river width of the target point in the river in the remote sensing image of the river, the method further includes:

and substituting the inclination angle of the straight line corresponding to the minimum one of the straight line distances of the two banks into any straight line equation expression passing through the target point in the river channel to obtain a river width measurement line straight line equation passing through the target point in the river channel, and determining a corresponding river width measurement line by the river width measurement line straight line equation.

Optionally, the substituting the inclination angle of the straight line corresponding to the minimum one of the linear distances between the two banks into any linear equation expression passing through the target point in the river channel to obtain a river width measurement line linear equation passing through the target point in the river channel, and determining the corresponding river width measurement line by using the river width measurement line linear equation specifically includes:

judging the number of straight lines corresponding to the smallest of the straight line distances of the two banks;

when the number of the target points is one, substituting the inclination angle of the straight line corresponding to the minimum one of the straight line distances of the two banks into any straight line equation expression passing through the target point in the river channel to obtain a river width measurement line straight line equation passing through the target point in the river channel, and determining a corresponding river width measurement line by the river width measurement line straight line equation;

and when the number of the target points is more than one, determining the median of the inclination angles of the straight lines corresponding to the minimum of the straight line distances of the two banks, substituting the median into any straight line equation expression passing through the target point in the river channel to obtain a river width measurement line linear equation passing through the target point in the river channel, and determining the corresponding river width measurement line by using the river width measurement line linear equation.

The invention also provides a system for measuring and calculating the width of the water surface of the whole river water area, which comprises:

the image acquisition module is used for acquiring a riverway remote sensing image;

the image dividing module is used for determining an internal river channel image and an external river channel image in the remote river channel sensing image;

the straight line set determining module is used for determining a set formed by a plurality of straight lines passing through a target point in a river channel in the remote sensing image of the river channel as a target straight line set; setting linear inclination angle sampling interval values at intervals of the inclination angles of any two adjacent straight lines in the target straight line set; the inclination angle is an included angle between a straight line and a transverse axis of a rectangular coordinate system; the rectangular coordinate system is a coordinate system established by taking the target point in the river as the center of a circle, taking the east to the west as a horizontal axis and taking the south to the north as a longitudinal axis; the target point in the river channel is any one pixel point in the image in the river channel;

the pixel point coordinate determination module is used for determining a linear pixel point coordinate set of each straight line in the target straight line set based on a preset maximum detection river width threshold value and the target point in the river channel; the linear pixel point coordinate set is a set of coordinates of pixels of which straight lines pass through the riverway remote sensing image;

the intersection point coordinate determination module is used for calculating the pixel coordinate of the left intersection point and the pixel coordinate of the right intersection point of each straight line in the target straight line set based on the straight line pixel point coordinate set; the left intersection point is a pixel point which is formed by the intersection of a straight line and a river channel left bank positioned on one side of a target point in the river channel; the right intersection point is a pixel point of a straight line intersected with the right bank of the river channel positioned on the other side of the target point in the river channel;

the intersection point distance calculation module is used for calculating the pixel point distance between the pixel coordinate of any one left intersection point and the pixel coordinate of any one right intersection point corresponding to each straight line and determining the minimum pixel point distance as the straight line distance between two banks of the corresponding straight line;

and the river width calculation module is used for determining the minimum one of the linear distances between the two banks as the river width of a target point in the river channel remote sensing image.

Compared with the prior art, the invention has the beneficial effects that:

the invention provides a method and a system for measuring and calculating the water surface width of a whole river water area, which can measure the river width value of a corresponding position at any point on the water surface of a river and realize the measurement and calculation of the water surface width of the whole river water area (namely, at any point in a river channel); the method does not depend on the river channel center line extraction process, thereby eliminating error transfer generated by extracting the river channel center line firstly and then calculating the corresponding river width. The method can realize the high-efficiency and high-precision measurement and calculation of large-range and dynamic river width, and improves the precision and efficiency of remote sensing estimation of the runoff of the surface river.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.

Fig. 1 is a schematic diagram of an analytic computing principle of an indeterminate equation algorithm for river width measurement and calculation according to an embodiment of the present invention;

fig. 2 is a flowchart of a method for measuring and calculating the width of the water surface of the whole river basin according to an embodiment of the present invention;

fig. 3 is a schematic diagram illustrating a principle of discrete pixel calculation of a remote sensing image by using an indeterminate equation algorithm for river width measurement and calculation provided by the embodiment of the invention;

FIG. 4 is a schematic diagram of an original remote sensing image and classification results;

FIG. 5 is a schematic view of a river width measurement line at any point position in a river and a spatial distribution of river width values at the measured point position;

fig. 6 is a space distribution of water surface width values and a riverway water surface width equivalent diagram.

Fig. 7 is a schematic structural diagram of a system for measuring and calculating the width of the water surface of the whole river basin according to an embodiment of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.

According to the traditional river width definition method, the distance between a perpendicular line passing through one point on the center line of the river channel and the intersection points of two banks of the river channel is the river width corresponding to the changed point. Wherein, the perpendicular line of a point on the center line of the river course is the straight line with the shortest intersection point distance between any straight line passing through the point and the two banks of the river course. However, the traditional river width definition does not provide complete and uniform definitions for the situations of river channel central line non-guidance, intersection of multiple river channel central lines, non-river channel central line positions and the like, and river width measurement and calculation depend on extraction of the river channel central lines.

In order to solve the problems that the traditional River Width extraction method depends on the extraction result of the center line of the River channel, the definition of the bent or intersected position of the River channel is unclear and measuring and calculating errors are easy to superpose, the invention provides a River Width measuring and calculating method, namely an Indeterminate Equation Algorithm (riverwidth estimated based River Width Algorithm) for River Width measurement and calculation, which is called riverwidth IE Algorithm for short. The method constructs an indefinite equation according to any point on the river surface and automatically measures and calculates the river surface width based on the remote sensing image, so that the large-range and long-time-sequence automatic measurement and calculation of the river full-water-area water surface width can be realized. Compared with the traditional river width measuring and calculating method, the river width measuring and calculating result of the method at the center line of the river channel is equivalent to that of the traditional method; besides, the river width value at any point of the river water surface except the center line of the river channel can be measured and calculated by the method.

Compared with the traditional river width measuring and calculating method based on river channel center line extraction, the river width defining method provided by the invention is simpler and has stronger applicability, the defect of the traditional method in the whole water surface width measuring and calculating method is overcome, and the automatic extraction efficiency and precision of large-range and dynamic river width measuring and calculating can be improved.

The invention provides a new definition of river width measurement, namely: the width of a river can be defined as "the minimum length of any straight segment connecting the two banks of the river and passing through a designated point in the river". The above definition is equivalent to the traditional river width definition method on the center line of the river channel as can be proved by a geometric method, and the definition can also be used for measuring and calculating the water surface width of the whole river water area (namely, of any point in the river channel) outside the center line of the river channel.

Based on the above definition, the invention provides a river WidthIE algorithm. The analytic calculation principle of the river WidthIE algorithm is as follows:

first, an indefinite equation representation of "an arbitrary straight line through a point in the river" is given. Let the given point O coordinate in the river be (x)₀,y₀) The included angle between the straight line passing through the point and the horizontal direction of the plane coordinate axis is theta (theta is more than or equal to 0)<Pi), it is customary to specify in the remote sensing image that the x-axis of the plane coordinate axes is from west to east and the y-axis is from south to north. The point O (x) is crossed₀,y₀) Can be expressed as:

y-y₀＝tanθ·(x-x₀) (θ ≠ π/2) (equation 1)

Where (x, y) is the coordinates of a point on the straight line, and tan θ is the slope of the straight line. When theta is pi/2, the straight line is perpendicular to the direction of the x axis of the coordinate axes, and only x is x₀，-∞<y<And + ∞. This equation shows that equation 1 can represent the passing point O (x) as the included angle theta changes₀,y₀) As shown in fig. 1.

Then, an analytic expression method corresponding to the width of the river channel is given. Define "river banks" as the boundary between water and non-water in the image, where the left bank F_LRight bank F_RExpressed by functional equations respectively:

F_L(x, y) ═ 0 (equation 2)

F_R(x, y) ═ 0 (equation 3)

For a given point O coordinate (x)₀,y₀) And the slope tan theta of the straight line in the indefinite equation (0 ≦ theta)<Pi and theta is not equal to pi/2), combining the formula 1 and the formula 2 and solving to obtain an intersection point of a straight line passing through the point O and having a slope of tan theta and the left bank, and marking the intersection point as a point E '(x'₁,y′₁) (ii) a The formula 1 and the formula 3 are combined and solved, and the intersection point of the straight line passing through the point O and having the slope tan theta and the right bank is obtained and is marked as a point F' (x)′₂,y′₂) Namely:

point E '(x'₁,y′₁) Satisfy the system of equations

Point F '(x'₂,y′₂) Satisfy the system of equations

The euclidean distance between the straight line represented by the indefinite equation and the intersection of the two banks of the river is:

for the case of θ ═ π/2, the indeterminate equation becomes x ═ x₀，-∞<y<+∞，D_E′F′The calculation method of (3) is the same as above. In addition, for a given line corresponding to the value of θ, if there is no intersection with the left bank or the right bank of the river, i.e., points E 'or F' do not exist, the calculation D is discarded_E′F′。

Thus, for all values of θ within the specified range (0 ≦ θ)<N) must be present in D_E′F′Minimum value of D_EFAnd the intersection points of the corresponding straight line and the two banks of the river are respectively marked as E and F. Then calculate D_EFThe straight line section EF is a corresponding river width measurement line. Can be expressed by the following formula:

D_EF＝min{D_E′F′}(0≤θ<pi) (equation 5)

The river full-water-area water surface width measuring and calculating method of the embodiment is that a riverwidth IE algorithm is used for carrying out discrete pixel calculation on a remote sensing image, the discrete pixel calculation and analysis calculation principle of the riverwidth IE algorithm is the same, and the river full-water-area water surface width measuring and calculating method mainly comprises the following algorithm modules: a first module, wherein any straight line passing through one point in a river course passes through a pixel coordinate representation module in an image; a module II, a module for calculating the intersection point of a straight line passing through one point in the river channel and two banks of the river channel; a module III, a judging module with three collinear points and different sides; and a fourth module for determining the river width value.

The function calling method of each module comprises the following steps: first, an O coordinate (x) of a given point (target point in a river) in the river is set₀,y₀) Presetting three groups of parameters including a maximum detection river width threshold value delta and setting a linear inclination angle sampling interval value omega; then, determining the inclination angle theta (0 ≦ theta) of a series of straight lines<Pi), making the value interval of adjacent theta be omega, and determining pixel sets AB and CD respectively corresponding to the left bank and the right bank of the river channel by adopting an image processing method; next, the module is modeled based on the point O coordinate (x)₀,y₀) Determining a pixel coordinate set EF in an image through which a corresponding straight line passes by according to a river width threshold value delta and a current straight line inclination angle theta_θ(ii) a Subsequently, module two calculates the current set EF_θIntersection pixel coordinates with the sets AB and CD respectively; then, for the case of intersection, the third module determines whether the pixels of intersection are collinear with the point O and on both sides of the point O, and retains a group of pixel sets satisfying the condition; and finally, determining that the shortest distance among the groups of pixel sets meeting the conditions is the river width value corresponding to the given point in the current river channel by continuously changing the value of the inclination angle theta by the module IV.

Fig. 2 is a flowchart of a method for measuring and calculating the width of the water surface of the whole river basin according to the embodiment of the invention. Referring to fig. 2, the method for measuring and calculating the water surface width of the whole river water area of the embodiment includes:

step 101: and acquiring a river channel remote sensing image.

Step 102: and determining an internal river channel image and an external river channel image in the remote river channel sensing image.

Step 103: determining a set formed by a plurality of straight lines passing through target points in the riverway remote sensing image as a target straight line set; setting linear inclination angle sampling interval values at intervals of the inclination angles of any two adjacent straight lines in the target straight line set; the inclination angle is an included angle between a straight line and a cross shaft of the rectangular coordinate system.

The rectangular coordinate system is a coordinate system established by taking the target point in the river as the center of a circle, taking the east to the west as a horizontal axis and taking the south to the north as a longitudinal axis; the target point in the river channel is any pixel point in the image in the river channel.

Step 104: determining a linear pixel point coordinate set of each straight line in the target straight line set based on a preset maximum detection river width threshold and the target point in the river channel; the linear pixel point coordinate set is a set of coordinates of pixels of which straight lines pass through the riverway remote sensing image.

The step 104 specifically includes:

and when the inclination angle of the straight line is equal to pi/2, determining a linear pixel point coordinate set by presetting a maximum detection river width threshold and a row of pixels where target points in the river channel are located. And when the inclination angle of the straight line is not equal to pi/2, determining a coordinate set of straight line pixel points by adopting an indeterminate equation algorithm based on a preset maximum detection river width threshold value and the target points in the river channel.

When the inclination angle of the straight line is not equal to pi/2, based on a preset maximum detection river width threshold value and the target point in the river channel, determining a coordinate set of straight line pixel points by adopting an indeterminate equation algorithm, specifically:

and selecting the abscissa according to the preset maximum detection river width threshold and the abscissa of the target point in the river channel at set intervals to obtain a first abscissa continuous integer sequence.

Substituting the first abscissa continuous integer sequence into any linear equation expression of a target point in the river channel, and performing upward rounding operation on the obtained ordinate continuous integer sequence corresponding to the first abscissa continuous integer sequence to obtain a first ordinate continuous integer sequence; the first abscissa continuous integer sequence and the first ordinate continuous integer sequence constitute a first pixel point coordinate sequence.

And selecting the vertical coordinate according to the preset maximum detection river width threshold value and the vertical coordinate of the target point in the river channel at set intervals to obtain a second vertical coordinate continuous integer sequence.

Substituting the second continuous integer sequence of the ordinate into any linear equation expression of a target point in the river channel, and performing upward rounding operation on the obtained continuous integer sequence of the abscissa corresponding to the second continuous integer sequence of the ordinate to obtain a second continuous integer sequence of the abscissa; and the second abscissa continuous integer sequence and the second ordinate continuous integer sequence form a second pixel point coordinate sequence.

Step 105: calculating the pixel coordinates of the left intersection point and the pixel coordinates of the right intersection point of all straight lines in the target straight line set based on the straight line pixel point coordinate set; the left intersection point is a pixel point which is formed by the intersection of a straight line and a river channel left bank positioned on one side of a target point in the river channel; and the right intersection point is a pixel point which is formed by a straight line and the right bank of the river channel positioned on the other side of the target point in the river channel.

The step 105 specifically includes:

and determining a pixel coordinate set of a left bank of the river channel and a pixel coordinate set of a right bank of the river channel in the remote sensing image of the river channel.

And calculating the intersection of the pixel coordinate set of the left bank of the river channel and the linear pixel point coordinate set to obtain the intersection point coordinate of the left bank.

And calculating the intersection of the pixel coordinate set of the right bank of the river channel and the linear pixel point coordinate set to obtain the intersection point coordinate of the right bank.

Substituting any one left bank intersection point coordinate and any one right bank intersection point coordinate into an intersection point judgment formula; the intersection point judgment formula is that the angle EOF is greater than pi 2; wherein O represents a target point in the river; e represents a left bank intersection point; f represents a right bank intersection point; the angle EOF is an angle with O as a vertex and with OE and OF as two edges; one calculation way to satisfy the intersection point determination formula may be:

wherein (x)_Eθ,y_Eθ) The coordinates of the left bank intersection point of the straight line with the inclination angle theta; (x)_Fθ,y_Fθ) The right bank intersection point coordinate of the straight line with the inclination angle theta; (x)₀,y₀) Is composed ofCoordinates of target points in the river; o represents a target point in the river;

is a vector from the point O to the point E;

is a vector from point O to point F. If formula 6 is satisfied, the intersection point determination formula is considered to be the EOF>π/2。

Step 106: and calculating the pixel point distance between the pixel coordinate of any one left intersection point and the pixel coordinate of any one right intersection point corresponding to each straight line, and determining the minimum pixel point distance as the straight line distance between two banks of the corresponding straight line. The method specifically comprises the following steps:

Step 107: and determining the minimum one of the linear distances between the two banks as the river width of the target point in the river channel remote sensing image.

As an optional implementation manner, after the step 107, the method further includes:

substituting the inclination angle of the straight line corresponding to the minimum one of the straight line distances of the two banks into any straight line equation expression (formula 1) passing through the target point in the river channel to obtain a river width measurement line straight line equation passing through the target point in the river channel, and determining a corresponding river width measurement line straight line equation according to the river width measurement line straight line equation to determine a corresponding river width measurement line. Specifically, the method comprises the following steps:

and judging the number of the straight lines corresponding to the smallest of all the straight line distances between the two banks.

And when the number of the target points is one, substituting the inclination angle of the straight line corresponding to the minimum one of the straight line distances of the two banks into any straight line equation expression passing through the target point in the river channel to obtain a river width measurement line straight line equation passing through the target point in the river channel, and determining the corresponding river width measurement line according to the river width measurement line straight line equation.

In practical application, a specific implementation process of the method for measuring and calculating the width of the water surface of the whole river water area in the embodiment is as follows:

(1) determining pixel coordinates of any straight line passing through one point in river channel in image

Passing through a point O (x)₀,y₀) The coordinate of the pixel through which the straight line of (a) passes is expressed as (x)₁,y₁),(x₂,y₂),…,(x_j,y_j) Wherein x is₀,x₁,x₂,…,x_jAnd y₀,y₁,y₂,…,y_jAre all positive integers and have x₁,x₂,…,x_j∈[x₀-δ,x₀+δ]And y is₁,y₂,…,y_j∈[y₀-δ,y₀+δ]. Where δ is a positive integer and is an empirically given parameter. Delta denotes the passing point O (x)₀,y₀) If the intersection point of the straight line and the two banks cannot be found in the window taking delta as the radius near the point O, the fact that the current straight line cannot be a river width measuring line passing the point O is shown. In this embodiment, the value of δ is greater than the rounding value of the maximum width of the known river channel in the image. (x) is given below₁,y₁),(x₂,y₂),…,(x_j,y_j) The method of (3).

First, (x)₀,y₀) Is the pixel coordinate of any point in the river channel in the image, namely the target point in the river channel, x₀，y₀Is a positive integer, x₀Is the abscissa, y, of the target point in the river₀Is the ordinate of the target point in the river channel. Taking a sequence of consecutive integers x_p1,x_p2,…,x_pi,…,x_pk∈[x₀-δ,x₀+δ](where k is 2 δ +1), the first abscissa consecutive integer sequence is obtained. And substituting the first abscissa continuous integer sequence into an indefinite equation, namely, substituting the first abscissa continuous integer sequence into any linear equation expression (formula 1) passing through a target point in the river channel to obtain a series of values of y related to the included angle theta. Then, for a given included angle theta, rounding up the values of the series of y to obtain the corresponding y_p1,y_p2,…,y_pi,…,y_pk(pi is more than or equal to 1 and less than or equal to 2 delta +1), and obtaining a first ordinate continuous integer sequence. Wherein,

y_pi＝ceil[f(x_pi,θ)]＝ceil[tanθ·(x_pi-x₀)+y₀](θ ≠ π/2) (equation 8)

Where ceil represents a ceiling operation. 1,2, …, k, (x)_p1,y_p1),(x_p2,y_p2),…,(x_pk,y_pk) And obtaining the coordinate sequence of the first pixel point for the coordinate of the pixel point passed by the straight line.

Similarly, the coordinate sequence (x) calculated according to equation 8 is due to the slope of the line and the influence of the rounding calculation_pk,y_pk) Not necessarily contiguous and adjacent and therefore may result in no intersection with the riverway shoal pixel coordinates. To avoid this, the sequence of consecutive integers y should be taken again_q1,y_q2,…,y_qi,…,y_qk∈[y₀-δ,y₀+δ](where k is 2 δ +1), a second ordinate-continuous integer sequence is obtained. Substituting the first vertical coordinate continuous integer sequence into any linear equation expression (formula 1) passing through a target point in the river channel to obtain the sumA series of x values associated with the angle theta. Then, for a given included angle theta, rounding up a series of x values to obtain corresponding x_q1,x_q2,…,x_qi,…,x_qk(qi is more than or equal to 1 and less than or equal to 2 delta +1), and obtaining a second abscissa continuous integer sequence. Wherein,

x_qi＝ceil[f^-1(y_qi,θ)]＝ceil[(y_qi-y₀)/tanθ+x₀](θ ≠ π/2) (equation 9)

Where ceil represents a ceiling operation. 1,2, …, k, (x)_q1,y_q1),(x_q2,y_q2),…,(x_qk,y_qk) And obtaining a second pixel point coordinate sequence for the pixel point coordinate passed by the straight line.

For the two groups of values, repeated pixel point coordinates may exist, so that for a given included angle theta value, all pixel point coordinates through which a straight line passes can be solved through Union set (Union) operation. Let EF be a set of pixels (linear pixel coordinate set) through which a straight line passing through the point O passes for a given included angle theta value (theta ≠ pi/2)_θ＝{(x₁,y₁),(x₂,y₂),…,(x_j,y_j) And then, there are:

EF_θ＝{(x_p1,y_p1),(x_p2,y_p2),…,(x_pk,y_pk)}∪{(x_q1,y_q1),(x_q2,y_q2),…,(x_qk,y_qk)}

＝{(x₁,y₁),(x₂,y₂),…,(x_j,y_j)}

(formula 10)

In addition, in the case where θ ═ pi/2 excluded from the formula 9 in the above formula 8, that is, the straight line is perpendicular to the x-axis direction, the abscissa of the point where the straight line passes is the same, that is, x ═ x₀The ordinate takes [ y₀-δ,y₀+δ]The integer of the interval, that is, the coordinate set of the pixel points through which the straight line passes when θ is pi/2 (the coordinate set of the straight line pixel points) is as follows:

EF_θ＝π/2＝{(x₀,y₀-δ),(x₀,y₀-δ+1),…,(x₀,y₀+δ-1),(x₀,y₀+δ)}

(formula 11)

Wherein x is₀，y₀And δ are both positive integers. And substituting different values of theta into the formula 1 to obtain pixel point coordinate sets corresponding to different linear equations.

(2) Calculating the intersection point of a straight line crossing one point in the river channel and two banks of the river channel

Suppose that the two banks of the river can be represented by a coordinate line of a series of points. For points on the remote sensing image, the equation of a connecting line of the points on two sides of the river channel and the passing point O (x) do not need to be solved₀,y₀) The intersection point coordinates of the indefinite equation are calculated, and the intersection of the pixel point coordinate set passed by the indefinite equation (formula 1) and the corresponding pixel coordinates of the two banks of the river channel is only needed to be calculated. As shown in fig. 3, the left bank and the right bank of the river are denoted by AB and CD, respectively. The sets of pixel coordinates corresponding to AB and CD in the image are respectively:

AB＝{(x_A1,y_A1),(x_A2,y_A2),…,(x_Am,y_Am)}

CD＝{(x_C1,y_C1),(x_C2,y_C2),…,(x_Cn,y_Cn)}

(formula 12)

The coordinates of the Intersection of the straight line passing through the point O and the two banks can be obtained approximately by Intersection (Intersection) operation of the sets. Wherein, for a given included angle theta value, the coordinates of the intersection points of the straight line, the left bank AB and the right bank CD are respectively E (x)_Eθ,y_Eθ)，F(x_Fθ,y_Fθ) The calculation method is as follows:

wherein, EF_θThe coordinate set of image pixel points which are passed through the O point and passed through by the straight line with the included angle theta with the x-axis direction, AB and CD respectively represent the left side of the river channelAnd (4) collecting the coordinates of the image pixel points corresponding to the bank and the right bank. If intersection (x)_Eθ,y_Eθ) Or (x)_Fθ,y_Fθ) Is an empty collector

The included angle between the slope of the current straight line and the center line of the river channel is too small, and the included angle cannot be a river width measuring line and is discarded.

(3) Determine three points to be collinear and opposite

Due to the complexity of the river network structure, when there are river channel curves, plaited rivers, etc., in a given window range δ, the intersection point E, F of the straight line passing through the point O and the left bank AB and the right bank CD must be collinear with the point O, but there may be more than one pair, so that the following determination condition needs to be satisfied in order to find a river width measurement line passing through the point O:

1) the two intersection points must belong to different river banks and are distributed on two sides of the point O;

2) the two intersection points are the minimum distance between two points among all the intersection points satisfying the condition 1).

Since the rounding operations are performed by the equations 8 and 9, the mathematical expression for the determination condition 1) can be appropriately relaxed, i.e., pi/2 must be satisfied<Less than or equal to pi for EOF or vector

And

the included angle of (a) is an obtuse angle. According to the cosine formula of the vector angle, a formula 6 can be obtained.

If the intersection E, F and the point O satisfy the above constraint (equation 6), it indicates that the points E, F belonging to the same straight line are on the straight line passing through the point O and are on both sides of the point O. Namely, a set of pixel coordinates of the left intersection point and a set of pixel coordinates of the right intersection point are obtained.

(4) Determining the shortest distance between the left and right intersections, i.e. determining the river width

For 0 ≦ θ<And pi, sampling the value of theta at a certain interval omega. For example, if ω is pi/180, then θ may take a total of 180 different values such as 0,2 ω,3 ω, …,179 ω, etc. Then, the user can use the device to perform the operation,substituting (formula 1) - (formula 5), (formula 8) - (formula 13) to calculate the corresponding linear equation and intersection point coordinates. For each intersection point with the two banks generated by different theta values (which can be understood as the intersection point formed by the straight line and the two banks in turn in the continuous rotation process with the point O as the axis), whether the intersection points are on different sides of the point O is judged according to the method of (formula 6), and if so, the intersection point E (x) is used_Eθ,y_Eθ) Put into the set of pixel coordinates of the left intersection point, and put the intersection point F (x)_Fθ,y_Fθ) Putting the intersection points into a set of pixel coordinates of the right intersection point, and if not, discarding a pair of intersection points E (x) corresponding to the current theta value_Eθ,y_Eθ)，F(x_Fθ,y_Fθ). Pixel point distance | EF between pixel coordinates of left intersection point and pixel coordinates of right intersection point_θThe formula for | is shown in formula 7, i.e.

Wherein theta is more than or equal to 0<π，

And (x)_Eθ′，y_Eθ′)，(x_Fθ′，y_Fθ') satisfies equation 6. Obviously, when the value of the interval ω is sufficiently small, the corresponding minimum | EF of θ in the value range can be found_θValue of | EF_θ|_min. In fact, too small value of ω increases the calculation amount in the above process, so that the distance between two straight line segments passing through the O point corresponding to θ and θ + ω is only required to be less than 1 unit pixel width at the end, i.e., ω is less than or equal to 1/δ, and δ represents half of the length of the straight line segment passing through the O point, as described above.

Finally, a pair of intersection points meeting the judgment condition 2) is solved, the pixel distance between the two points is calculated, and then the actual geographic space distance is converted according to the space scale represented by each pixel, namely the river width value W corresponding to the current point O, and the expression is as follows:

W＝min{|EF_θ|_min0 ≦ θ < π | } (equation 14)

And substituting the theta value corresponding to the W into an equation (formula 1) to obtain a mathematical expression of the river width measuring line EF passing through the current point O.

And if the lengths of the river width measuring lines corresponding to the theta values are equal, selecting the river width measuring line corresponding to the median of the theta values as the finally determined river width measuring line. If all the theta values of the point O in the river channel do not have the point E, F meeting the condition of the formula 6, the maximum detection river width threshold value delta is small, and the process can be executed again after the threshold value delta is enlarged to calculate the river width.

The method for measuring and calculating the water surface width of the whole river water area overcomes the problem that the traditional method for measuring and calculating the river width depends on the extraction result of the center line of the river channel, so that errors are accumulated, the consistency of the traditional method for measuring and calculating the water surface width of the whole river water area (namely any point in the river channel) outside the center line of the river channel is kept, and the process can realize full automation. The method is independent of each other for calculation of each point in the river channel, so that the method is suitable for parallel calculation, and the production efficiency of large-range and long-time river width data is improved.

An embodiment will be provided to explain the effect of the method for measuring and calculating the water surface width of the whole river.

The method comprises the steps of selecting a surface reflectance remote sensing image obtained by an OLI (on-line analytical instrument) sensor of Landsat8 satellite at a certain section of the Yangtze river main flow in China, wherein the spatial resolution of the image is 30 meters, and the size of the remote sensing image of the selected area is 440 multiplied by 440 pixels. The maximum width of the river surface in the area is about 2500 meters, a huge sandbank is formed to divide the runoff into two parts, and the area of the sandbank changes along with seasons, so that the width of the water surface changes along with the change.

(1) Applicability of the invention to various types of remote sensing images

The process of measuring and calculating the river width is established on the basis of accurately extracting the river channel pixels, so that the applicable remote sensing images can be various common remote sensing images with different types and different resolutions such as multispectral, hyperspectral or Synthetic Aperture Radar (SAR), and the river channel pixels can be accurately identified only by the requirement of the remote sensing images.

In this embodiment, the obtained Landsat8 remote sensing image is subjected to image classification, the image is classified into a Water body (Surface Water), a Vegetation (Vegetation) and other Land types (Land including a building Land, a bare soil and the like) by adopting an unsupervised classification IsoDATA algorithm, pixels belonging to a River (River) are further determined from the Water body type by adopting a region growing method, the original remote sensing image is shown as part (a) in fig. 4, and the corresponding classification result is shown as part (b) in fig. 4.

(2) The river width measuring and calculating method is applicable to river width measuring and calculating under the condition that river channels change at different time

The process of measuring and calculating the river width does not depend on the extraction result of the center line of the river channel, so that the corresponding river width value can be measured and calculated even if the point position of the river width to be measured is not on the center line of the river channel. When river channel form changes are caused by river water rising, diversion and the like, river width values of the same point before and after the changes can be measured through the successively acquired remote sensing images, so that the river width changes can be directly compared, and the flow changes can be further calculated. A schematic view of a river width measurement line at any point position in the river is shown in part (a) of fig. 5, and a spatial distribution diagram of river width values at the measured point position is shown in part (b) of fig. 5.

(3) The invention has applicability to automatic measurement and calculation of water surface width of river whole water area

The method can also be used for automatically measuring and calculating the water surface width value of the whole river water area to obtain the equivalent river water surface width map. The river width value of each pixel position calculated by the river width IE algorithm provided by the invention is independent, so that the river width IE algorithm is suitable for calculating the water surface width value corresponding to each pixel point in the whole river water area in parallel, and a river water surface width equivalent map can be drawn according to the space distribution diagram of the water surface width value, so that a more concise and visual water surface width map of the whole river water area is obtained.

In this embodiment, the river width corresponding to each pixel point in the full water area of the river is measured, a spatial distribution map of the obtained water surface width value is shown in part (a) of fig. 6, and a diagram for drawing an equivalent value of the water surface width of the river is shown in part (b) of fig. 6.

According to the above example, the width of the main river channel of the Yangtze river is about 2475.1 m at the widest part, about 560.4 m at the narrowest part, 1183.3 m at the median and 1287.4 m at the average in the range shown in the example. The narrowest point occurs near the sandbars forming the channel branches. Meanwhile, the result shows that the maximum value of the river width of the rest branches is 249.4 meters, the minimum value is 41.8 meters, and the highest measurement and calculation precision of the river width value is mainly limited by the resolution of the remote sensing image.

The invention also provides a system for measuring and calculating the water surface width of the whole river water area, which comprises the following components in percentage by weight with reference to fig. 7:

and the image acquisition module 201 is used for acquiring a river channel remote sensing image.

The image dividing module 202 is configured to determine an internal river image and an external river image in the remote river sensing image;

the straight line set determining module 203 is used for determining a set formed by a plurality of straight lines passing through a target point in a river channel in the remote sensing image of the river channel as a target straight line set; setting linear inclination angle sampling interval values at intervals of the inclination angles of any two adjacent straight lines in the target straight line set; the inclination angle is an included angle between a straight line and a transverse axis of a rectangular coordinate system; the rectangular coordinate system is a coordinate system established by taking the target point in the river as the center of a circle, taking the east to the west as a horizontal axis and taking the south to the north as a longitudinal axis; the target point in the river channel is any pixel point in the image in the river channel.

A pixel point coordinate determination module 204, configured to determine a linear pixel point coordinate set of each straight line in the target straight line set based on a preset maximum detected river width threshold and the target point in the river; the linear pixel point coordinate set is a set of coordinates of pixels of which straight lines pass through the riverway remote sensing image.

An intersection coordinate determination module 205, configured to calculate, based on the linear pixel point coordinate set, a pixel coordinate of a left intersection and a pixel coordinate of a right intersection of each straight line in the target linear set; the left intersection point is a pixel point which is formed by the intersection of a straight line and a river channel left bank positioned on one side of a target point in the river channel; and the right intersection point is a pixel point which is formed by a straight line and the right bank of the river channel positioned on the other side of the target point in the river channel.

And the intersection point distance calculation module 206 is configured to calculate a pixel point distance between the pixel coordinate of any one of the left intersection points and the pixel coordinate of any one of the right intersection points corresponding to each straight line, and determine a minimum pixel point distance as a straight line distance between two banks of the corresponding straight line.

And the river width calculation module 207 is configured to determine the smallest one of the linear distances between all the two banks as the river width of the target point in the river channel remote sensing image.

The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. For the system disclosed by the embodiment, the description is relatively simple because the system corresponds to the method disclosed by the embodiment, and the relevant points can be referred to the method part for description.

The principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.

Claims

1. A method for measuring and calculating the water surface width of a river in the whole water area is characterized by comprising the following steps:

acquiring a riverway remote sensing image; determining pixels in the river channel and pixels outside the river channel in the river channel remote sensing image;

determining a linear pixel point coordinate set of each straight line in the target straight line set based on a preset maximum detection river width threshold and the target point in the river channel; the linear pixel point coordinate set is a set of coordinates of pixels of which straight lines pass through the riverway remote sensing image;

2. The method for measuring and calculating the water surface width of the whole river basin according to claim 1, wherein the determining a linear pixel point coordinate set of each straight line in the target straight line set based on a preset maximum detection river width threshold and a target point in the river channel specifically comprises:

when the inclination angle of the straight line is equal to pi/2, determining a linear pixel point coordinate set by presetting a maximum detection river width threshold and a row of pixels where target points in the river channel are located;

and when the inclination angle of the straight line is not equal to pi/2, determining a coordinate set of straight line pixel points by adopting an indeterminate equation algorithm based on a preset maximum detection river width threshold value and the target points in the river channel.

3. The method for measuring and calculating the water surface width of the whole river water area according to claim 2, wherein when the inclination angle of the straight line is not equal to pi/2, based on a preset maximum detection river width threshold and a target point in the river channel, an indeterminate equation algorithm is used for determining a coordinate set of straight line pixel points, and specifically comprises the following steps:

4. The method for measuring and calculating the width of the water surface of the whole river basin according to claim 1, wherein the calculating the pixel coordinates of the left intersection point and the pixel coordinates of the right intersection point of each straight line in the target straight line set based on the straight line pixel point coordinate set specifically comprises:

5. The method for measuring and calculating the width of the water surface of the whole river water area according to claim 1, wherein the calculating of the pixel point distance between the pixel coordinate of any one left intersection point and the pixel coordinate of any one right intersection point corresponding to each straight line specifically comprises:

6. The method for measuring and calculating the water surface width of the whole river water area according to claim 1, wherein after the step of determining the minimum of all the straight-line distances between the two banks as the river width of the target point in the river channel in the remote sensing image of the river channel, the method further comprises the following steps:

7. The method for measuring and calculating the water surface width of the whole river water area according to claim 6, wherein the step of substituting the inclination angle of the straight line corresponding to the minimum one of the linear distances between all the two banks into any linear equation expression passing through the target point in the river channel to obtain a river width measurement line linear equation passing through the target point in the river channel, and determining the corresponding river width measurement line by using the river width measurement line linear equation comprises the following steps:

8. A system for measuring and calculating the width of the water surface of the whole river water area is characterized by comprising: