A method for measuring forest gap characteristics in virtual forest scenes

Abstract

The present invention is a method for measuring forest window characteristics in a virtual forest scene, and the method for measuring forest window characteristics in a virtual forest scene includes the following steps: step S1, according to the attributes of the trees, select the trunk and branch models with similar data from the model library for matching, and construct a three-dimensional tree model; step S2, generate a virtual terrain according to the real terrain, and batch generate three-dimensional tree models with collision grids in the virtual scene to realize a virtual forest forest window scene; step S3, measure the forest window characteristics through the virtual forest forest window scene. The method for measuring forest window characteristics in a virtual forest scene proposed by the present invention makes up for the difficulty of the current field measurement research of forest window characteristics, provides method support for forestry digital simulation, and provides technical support for forest window measurement research in the field of forest ecology.

Description

Technical Field

[0001] The invention relates to the technical field of forestry digitization, and in particular to a method for measuring forest gap characteristics in a virtual forest scene. Background Art

[0002] Forest gaps are caused by small-scale disturbances such as fallen trees or large-scale disturbances such as insects, fires, and snowstorms. They can significantly increase the intensity of light under the forest, thereby changing the composition of forest communities. They are an important part of natural forest regeneration. At present, the definition of forest gaps has not been unified. In addition to size, they also have characteristics such as shape, effective light radiation, and three-dimensional structure. In field surveys, the shape of forest gaps is usually simplified, and two-dimensional projection is used to quickly measure the area of ​​forest gaps, but there are discrepancies with the actual value; the shapes of forest gaps mainly include dumbbells, ellipses, triangles, etc., but most forest gaps are irregular and cannot be accurately described; the three-dimensional spatial structure of forest gaps can be accurately measured by airborne laser radar, but the cost is high. The forest visualization simulation technology can not only build a three-dimensional model of trees and their environment based on actual survey data, and realistically restore the forest gap scene; it can also provide interactive objects and platforms for forest gap feature measurement research by building a large number of virtual forest simulation environments. Summary of the invention

[0003] The present invention provides a method for measuring forest gap characteristics in a virtual forest scene, characterized in that the method for measuring forest gap characteristics in a virtual forest scene comprises the following steps:

[0004] Step S1, according to the tree attributes, select the trunk and branch models with similar data from the model library for matching, and construct a three-dimensional tree model;

[0005] Step S2, generating a virtual terrain based on the real terrain, and batch-generating three-dimensional tree models with collision meshes in the virtual scene to realize a virtual forest window scene;

[0006] Step S3, measuring forest gap characteristics through a virtual forest gap scene;

[0007] The forest gap characteristics include forest gap edge trees, forest gap size, forest gap shape and forest gap three-dimensional structure;

[0008] The model library includes a trunk model library and a branch model library; the tree three-dimensional model obtains the matching trunk three-dimensional model of tree height and breast diameter from the trunk model library, and obtains the matching branch three-dimensional model of branch length and inclination from the branch model library.

[0009] Furthermore, in step S3, the forest gap edge tree measurement includes the following steps:

[0010] In the virtual forest gap scene, a point with a wide line of sight on the canopy height level inside the forest gap is selected as the position of the virtual camera;

[0011] In the horizontal direction of the virtual camera, collision rays are emitted from 0 to 360 degrees at intervals of n degrees. After colliding with the tree model, the model is highlighted;

[0012] Record the highlighted model information and remove duplicate data. The highlighted tree model is the forest gap edge tree;

[0013] The forest gap edge wood EdgeForestGap It is expressed as:

[0014] T EdgeForestGap =f HighLigth (f Camera (x,H canopy , y))

[0015] Among them, H canopy is the canopy height, n o is the rotation degree interval, f Camera Indicates the calculation of ray collision, f HighLigth Highlight the collision tree model, (x, H canopy , y) represents the virtual camera coordinates.

[0016] Furthermore, in step S3, the forest gap size measurement includes the following steps:

[0017] Place the virtual camera above the forest window and adjust it to a bird's-eye view. Take the virtual camera position as the origin of the spatial coordinate system, send out collision rays in the opposite direction of the z-axis, and scan around the y-axis (0°, 90°) at intervals of σ degrees.

[0018] When the collision ray collides with the canopy of the edge wood for the first time, the three-axis coordinates of the collision point are recorded and a coordinate point is generated. The coordinate point recorded at this time is the edge point of the forest window.

[0019] Rotate clockwise (0°, 360°) around the z-axis at intervals of β degrees, repeat the above steps, and finally obtain (360 / β) forest gap edge points;

[0020] Connect the marked points in sequence to generate polygons, and use the Shoelace Theorem formula to calculate the vertical projection area of ​​the forest gap;

[0021] The forest gap area S is expressed as:

[0022]

[0023] Among them, (x i ,y i ) is the vertical projection coordinate of the forest gap edge point i. In order to make all the marked points form a closed figure, the last marked point n is defined to be connected to the first point, and the x-axis coordinate of the first point in the calculation is defined as x n+1Same as x1, y-axis coordinate y n+1 Same as y1, n is the total number of marked points.

[0024] Furthermore, in step S3, the forest gap shape measurement includes the following steps:

[0025] According to the vertical projection coordinates of the generated forest gap edge marking points, connect the marking points and calculate the perimeter P, and use the shape index SI to represent the forest gap shape;

[0026] The forest gap perimeter P is expressed as:

[0027]

[0028] The shape index SI is expressed as:

[0029]

[0030] Where P is the perimeter of the forest gap, (x i ,y i ) is the vertical projection coordinate of the forest gap edge point i. In order to make all the marked points form a closed figure, the last marked point n is defined to be connected to the first point, and the x-axis coordinate of the first point in the calculation is defined as x n+1 Same as x1, y-axis coordinate y n+1 Same as y1, n is the number of marking points, and S is the forest gap area.

[0031] Furthermore, in step S3, the forest gap three-dimensional structure measurement includes the following steps:

[0032] Read the generated forest gap edge point spatial coordinates (x i ,y i , z i ), move the virtual camera to the same level as the forest gap edge and toward the forest gap edge point;

[0033] The camera descends at intervals of m meters until it is 1 meter above the ground. Each time it descends, the virtual camera sends a collision ray straight ahead. When it collides with the edge of the wood, the coordinates of the collision point are recorded and a marker point P is generated. ij ;

[0034] After generating a round of marking points, restore the virtual camera to the next forest window edge point P i+1 On the same horizontal plane, rotate β degrees clockwise around the z axis, and now it is heading towards the edge point P i+1 , repeat the above operation to generate a new round of marking points P i+1j .

[0035] Repeat the process for all forest gap edge points, and finally the total number of marker points generated is ((zi-1) / m))*(360 / β); iInstead of generating a marker point P ij Connect and connect the edge points of each forest gap to form a three-dimensional structure of the forest gap.

[0036] The i-th forest gap edge point corresponds to the coordinates of the marked point below P ij :

[0037] P ij =f Ray (x i ,y i , z i -j×m)

[0038] Among them, (x i ,y i , z i ) is the forest gap edge point P i Coordinates, j takes values ​​of (1, 2, 3, ..., (z i -1) / m), j×m is the camera descent height, f Ray (x i ,y i , z i -j×m) indicates the calculation of the collision point coordinates, that is, the collision ray from the virtual camera (x i ,y i , z i -j×m) coordinates, and the coordinates of the point where the camera collides with the 3D model of the tree.

[0039] The beneficial effects achieved by the present invention are:

[0040] The present invention proposes a method for measuring forest gap characteristics based on a virtual forest scene, which makes up for the difficulty of field measurement of forest gap characteristics. The method for generating a three-dimensional tree model based on a model library has strong scalability, is applicable to a variety of forest scenes, is easy to promote and apply, and provides method support for digital simulation of forestry.

[0041] Based on the adjustable forest gap measurement accuracy, the present invention can quickly obtain the forest gap characteristics in the forest scene, is easy to be applied in forest scenes of different scales, and provides technical support for forest gap measurement research in the field of forest ecology. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 A schematic diagram of a flow chart of a method for measuring forest gap characteristics in a virtual forest scene provided by an embodiment of the present invention;

[0043] Figure 2 A schematic diagram of measuring forest gap edge trees in a forest gap feature measurement method in a virtual forest scene provided by an embodiment of the present invention;

[0044] Figure 3A schematic diagram of measuring the size of a forest gap in a method for measuring forest gap characteristics in a virtual forest scene provided by an embodiment of the present invention;

[0045] Figure 4 A schematic diagram of a forest gap three-dimensional structure measurement in a forest gap feature measurement method in a virtual forest scene provided by an embodiment of the present invention;

[0046] Figure 5 A schematic diagram of a three-dimensional model of a Masson pine trunk in a method for measuring forest gap characteristics in a virtual forest scene provided by an embodiment of the present invention;

[0047] Figure 6 A schematic diagram of a three-dimensional model of a Masson pine branch in a method for measuring forest gap features in a virtual forest scene provided by an embodiment of the present invention;

[0048] Figure 7 A schematic diagram of a virtual Masson pine forest gap scene in a method for measuring forest gap characteristics in a virtual forest scene provided by an embodiment of the present invention;

[0049] Figure 8 A schematic diagram of measuring forest gap edge trees in a forest gap feature measurement method in a virtual forest scene provided by an embodiment of the present invention;

[0050] Fig. 9 A schematic diagram of marking edge points of forest gaps in a method for measuring forest gap features in a virtual forest scene provided by an embodiment of the present invention;

[0051] Fig.10 A schematic diagram of the three-dimensional structure measurement of a forest gap in a method for measuring forest gap features in a virtual forest scene provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0052] The technical solution of the present invention is described in more detail below in conjunction with the accompanying drawings. The present invention includes but is not limited to the following embodiments.

[0053] As attached Figure 1 As shown, the present invention proposes a method for measuring forest gap characteristics in a virtual forest scene, comprising the following steps:

[0054] S1, according to the tree attributes, select the trunk and branch models with similar data from the model library for matching and build the tree three-dimensional model;

[0055] S2, generates virtual terrain based on real terrain, and batch generates three-dimensional tree models with collision meshes in the virtual scene to realize the virtual forest window scene;

[0056] S3, measure forest gap characteristics through virtual forest gap scenes.

[0057] In step S1, SpeedTree plant modeling software is used to construct a tree model library according to the morphological and structural characteristics of the tree species. The model library includes a trunk model library Trunk and a branch model library Branch, wherein the trunk model library includes a plurality of trunk three-dimensional models of heights and diameters at breast height, and the branch model library includes a plurality of branch three-dimensional models of lengths and inclinations.

[0058] The trunk model library is:

[0059]

[0060] Where H is the height of the trunk, H min is the minimum height of the trunk, H max is the maximum height of the trunk, H step is the trunk height interval; D is the trunk diameter at breast height, D min is the minimum trunk diameter at breast height, D max is the maximum trunk diameter at breast height, D step is the trunk diameter interval. Assuming there are a height series and b diameter series, there are a×b trunk models in total.

[0061] Branch model library Branch:

[0062]

[0063] Where L is the length of the branch, L min is the minimum length of the branch, L max is the maximum length of the branch, L step is the branch length interval; A is the branch inclination angle, A min is the minimum inclination angle of the branch, A max is the maximum inclination angle of the branch, A step is the branch inclination interval. Assuming there are c length sequences and d inclination sequences, there are a total of c×d branch models.

[0064] According to the tree attributes, trunk and branch models with similar data are selected from the model library for matching, so as to generate a three-dimensional tree model that conforms to the morphological structure.

[0065] Tree 3D model Tree:

[0066]

[0067] Among them, f(Trunk[H]) and f(Trunk[D]) are the three-dimensional trunk models of tree height H and breast diameter D obtained by matching from the trunk model library, and f(Branch[L, A]) is the three-dimensional branch model of branch length and inclination obtained by matching from the branch model library.

[0068] In step S2, a virtual forest gap scene is constructed by Unity3D software, and the elevation grayscale image of the real terrain is imported to generate the terrain in the scene, and the length, width and height values ​​of the terrain are set so as to be proportional to the real terrain.

[0069] Terrain:

[0070] Terrain=f(DEM,length,width,height)

[0071] Among them, DEM is terrain elevation data, length is terrain length, width is terrain width, and height is terrain height.

[0072] When the tree coordinates are unknown, they can be randomly generated, or known tree coordinates can be imported to batch generate three-dimensional tree models with collision meshes in the virtual scene to realize a virtual forest window scene.

[0073] Forest:

[0074] Forest=f(Tree, Position, Direction)

[0075] Among them, Tree is the generated three-dimensional model of the tree, Position is the tree coordinate, and Direction is the direction of the tree.

[0076] In step S3, the forest gap features include forest gap edge trees, forest gap size, forest gap shape and forest gap three-dimensional structure. Measuring the forest gap features includes measuring forest gap edge trees, forest gap size, forest gap shape and forest gap three-dimensional structure.

[0077] The measurement of forest gap edge trees includes the following steps:

[0078] Forest gap edge trees refer to trees that surround forest gaps and reach the height of the canopy layer (H canopy ) trees, and determining the edge trees of forest gaps is a prerequisite for measuring the shape and size of forest gaps.

[0079] As attached Figure 2 As shown in the figure, in the virtual forest gap scene, a point (x, H canopy , y) as the position of the virtual camera; in the horizontal direction of the virtual camera, the collision rays are sequentially emitted from 0 to 360 degrees at intervals of n degrees. After colliding with the tree model, the model is highlighted, the highlighted model information is recorded and the duplicate data is removed. At this time, the highlighted tree model is the edge tree of the forest window (T EdgeForestGap ).

[0080] Z-axis rotation angle Rz: R z=Rotate(0,360,n°)

[0081] Forest gap edge wood EdgeForestGap It is expressed as:

[0082] T EdgeForestGap =f HighLigth (f Camera (x,H canopy , y))

[0083] Among them, H canopy is the canopy height, n o is the rotation degree interval, f Camera Indicates the calculation of ray collision, f HighLigth Highlight the collision tree model.

[0084] The gap size measurement includes the following steps:

[0085] After determining the edge trees of the forest gap, hide the non-edge trees. At this time, only the edge trees of the forest gap are displayed in the virtual forest scene.

[0086] As attached Figure 3 As shown in the figure, the virtual camera is placed above the forest window and adjusted to a bird's-eye view. With the virtual camera position as the origin of the spatial coordinates, a collision ray is emitted in the opposite direction of the z axis, and scanned around the y axis (0°, 90°) at intervals of σ degrees. When the ray collides with the edge forest canopy for the first time, the xyz coordinates of the edge point i of the forest window where the collision occurs are recorded and a coordinate point is generated. The recorded coordinate point is the forest window edge point. Then, at intervals of β degrees, rotate clockwise around the z axis (0°, 360°), repeat the above steps, and finally obtain n (n=360 / β) forest window edge points. Connect the edge points in turn to generate polygons, and use the Shoelace Theorem formula to calculate the vertical projection area of ​​the forest window.

[0087] Y-axis rotation angle Ry:

[0088] R y =Rotate(0, 90, σ°)

[0089] Z-axis rotation angle Rz:

[0090] R z =Rotate(0, 360, β°)

[0091] The forest gap area S is expressed as:

[0092]

[0093] Among them, (x i ,y i) is the vertical projection coordinate of edge point i. In order to make all edge points form a closed figure, the last edge point n is defined to be connected to the first point, and the x-axis coordinate of the first point in the calculation is defined as x n+1 Same as x1, y-axis coordinate y n+1 Same as y1, n is the total number of edge points.

[0094] The forest gap shape measurement includes the following steps:

[0095] According to the generated vertical projection coordinates of the forest gap edge points, the points are connected and the perimeter P is calculated, and the shape index SI is used to represent the forest gap shape.

[0096] Forest gap perimeter P:

[0097]

[0098] Shape Index SI:

[0099]

[0100] Where P is the perimeter of the forest gap, (x i ,y i ) is the vertical projection coordinate of edge point i. In order to make all the marked points form a closed figure, the last edge point n is defined to be connected to the first point, and the x-axis coordinate of the first point in the calculation is defined as x n+1 Same as x1, y-axis coordinate y n+1 Same as y1, n is the number of edge points, and S is the gap area.

[0101] The measurement of forest gap three-dimensional structure includes the following steps:

[0102] As attached Figure 4 As shown, the generated forest gap edge points P are read in sequence i Space coordinates (x i ,y i , z i ), move the virtual camera to the same level as the edge of the forest gap and toward P i ; Then it descends toward the z axis at intervals of m meters until it is 1 meter above the ground. Each descent sends a collision ray in front of the virtual camera. When it collides with the edge wood, the coordinates of the collision point are recorded and a marker point P is generated. ij ; After a round of scanning is completed, the marker point P is generated ij The number of (z i -1) / m; restore the virtual camera to the next forest window edge point P i+1 On the same horizontal plane, rotate β degrees clockwise around the z axis, and now it is heading towards the edge point P i+1 , repeat the above operation to generate a new round of marking points P i+1j; The final number of all generated marking points is ((zi-1) / m))*(360 / β); Connect each forest window edge point with its generated marking point, and connect each forest window edge point to form a forest window three-dimensional structure.

[0103] The i-th forest gap edge point corresponds to the coordinates of the marked point below P ij :

[0104] P ij =f Ray (x i ,y i , z i -j×m)

[0105] Z-axis rotation angle Rz:

[0106] R z =Rotate(0, 360, β°)

[0107] Among them, (x i ,y i , z i ) is the forest gap edge point P i Coordinates, j takes values ​​of (1, 2, 3, ..., (z i -1) / m), j×m is the camera descent height, f Ray (x i ,y i , z i -j×m) indicates the calculation of the collision point coordinates, that is, the collision ray from the virtual camera (x i ,y i , z i -j×m) coordinates, and the coordinates of the point where the camera collides with the 3D model of the tree.

[0108] Get all marked points P ij After obtaining the coordinates, the forest gap edge points are connected with the generated marking points, and the marking points of each forest gap are connected to generate the three-dimensional structure of the forest gap.

[0109] Specifically, the measurement method involved in the present invention is further described by taking the survey data (relative coordinates, tree height, DBH, and crown width) of 85 Masson pine trees provided by Fengyangshan Conservation Center of Baishanzu National Park as a specific example. The tree data is shown in Table 1.

[0110] Table 1 Forest data

[0111]

[0112] Construction of virtual Masson pine forest window scene

[0113] Construction of Masson pine trunk model library

[0114] Based on the survey data, Speed ​​Tree was used to construct a 3D model library of Masson pine trunks. min 10m, H max 30m, H step 5m; D min 5cm, D max 35cm, D step 5cm, a total of 35 tree trunk 3D models, Masson pine trunk 3D model as attached Figure 5 shown.

[0115] The value range of the tree trunk 3D model library is:

[0116]

[0117] Construction of Masson Pine Branch Model Library

[0118] Based on the survey data, Speed ​​Tree software was used to construct a three-dimensional model library of Masson pine branches, including L min 1.2m, L max 4.0m, L step 0.4m; A min is 30°, A max is 90°, A step The angle is 10°, with a total of 56 3D models of branches. The 3D model of the Masson pine trunk is shown in the attached figure. Figure 6 shown.

[0119] The value range of the Masson pine branch 3D model is:

[0120]

[0121] (3) Construction of virtual Masson pine forest gap scene

[0122] Based on the survey data, the DEM grayscale image of the survey plot was imported using Unity3D software, and the terrain length, width and height were set to 30m, 30m and 2m, respectively. A three-dimensional model of Masson pine was generated according to the tree attributes, and a virtual Masson pine forest gap scene was generated, as shown in the attached figure. Figure 7 shown.

[0123] Terrain:

[0124] Terrain=f(DEM, 30m, 30m, 2m)

[0125] Measurement of virtual Masson pine forest gap characteristics

[0126] (1) Measurement of forest gap edge trees in virtual forest scenes

[0127] Place the virtual camera in the forest window, take the lower left corner of the terrain as the coordinate origin, set the vertical height to the canopy height of 15m, and set the horizontal position to (15m, 15m). Scan the forest horizontally at 1 degree intervals to calculate the edge trees of the forest window. The calculation results are shown in the attached figure. Figure 8 shown.

[0128] Z-axis rotation angle Rz:

[0129] R z =Rotate(0, 360, 1°)

[0130] TEdgeForestGap:

[0131] T EdgeForestGap =f HighLigth (f Camera (15m, 15m, 15m))

[0132] Measuring forest gap size in virtual forest scenes

[0133] After determining the edge trees of the forest gap, hide the 3D models of other trees, set the camera height to 25m from the ground, and set the camera coordinates to (15m, 12m, 25m) so that the camera's top view covers the edge trees of the forest gap; scan the y-axis at 1 degree intervals and the z-axis at 5 degree intervals. The coordinates of the forest gap edge marker points (x i ,y i ), connect the edge points clockwise to form a polygon, as shown in the following figure Fig. 9 As shown in the figure, the gap area calculated by Shoelace Theorem is 56.41m 2 .

[0134] Y-axis rotation angle Ry:

[0135] R y =Rotate(0, 90, 1°)

[0136] Z-axis rotation angle Rz:

[0137] R z =Rotate(0, 360, 5°)

[0138] Forest gap area S:

[0139]

[0140] Measuring forest gap shape in virtual forest scenes

[0141] According to the generated vertical projection coordinates of the forest gap edge marking points, the perimeter P of the connecting marking points is calculated to be 37.73m, and the shape index SI is 1.42.

[0142] Forest gap perimeter P:

[0143]

[0144] Shape Index SI:

[0145]

[0146] Measurement of forest gap stereo structure in virtual forest scene

[0147] According to the coordinates of the forest gap edge points, the method proposed above was used to generate marking points by descending at intervals of 1 meter and rotating at intervals of 5 degrees; the forest gap edge points and their generated marking points were connected, and the forest gap edge points were connected to generate the three-dimensional structure of the Masson pine forest gap, as shown in the attached figure. Fig.10 shown.

[0148] The i-th forest gap edge point corresponds to the coordinates of the marked point below P ij :

[0149] P ij =f Ray (x i ,y i , z i -j×m), (x i ,y i , z i ) is the coordinate of the edge point of the forest gap, and j is taken as (1, 2, 3, ..., (z i -1) / m).

[0150] From the results, it can be seen that the forest gap feature measurement method in a virtual forest scene proposed by this invention has good universality. It can not only quickly measure forest gap features, but also select different forest gap feature measurement accuracies. It can improve the sense of participation and cognition of forestry research and related teaching, and meet the needs of forestry digital application.

[0151] The present invention is not limited to the above-mentioned specific implementation modes. A person skilled in the art may implement the present invention in various other specific implementation modes according to the embodiments and the disclosure of the drawings. Therefore, any design that adopts the design structure and concept of the present invention and makes some simple transformations or changes shall fall within the scope of protection of the present invention.

Claims

1. A method for measuring forest gap characteristics in a virtual forest scene, characterized in that: The method for measuring forest gap characteristics in a virtual forest scene comprises the following steps: Step S1, according to the tree attributes, select the trunk and branch models with similar data from the model library for matching, and construct a three-dimensional tree model; Step S2, generating a virtual terrain based on the real terrain, and batch-generating three-dimensional tree models with collision meshes in the virtual scene to realize a virtual forest window scene; Step S3, measuring forest gap characteristics through a virtual forest gap scene; The forest gap characteristics include forest gap edge trees, forest gap size, forest gap shape and forest gap three-dimensional structure; The model library includes a trunk model library and a branch model library; the tree three-dimensional model obtains a matching trunk three-dimensional model of tree height and breast diameter from the trunk model library, and obtains a matching branch three-dimensional model of branch length and inclination from the branch model library; The measurement of forest gap edge trees includes the following steps: In the virtual forest gap scene, a point with a wide line of sight on the canopy height level inside the forest gap is selected as the position of the virtual camera; In the horizontal direction of the virtual camera, collision rays are emitted from 0 to 360 degrees at intervals of n degrees. After colliding with the tree model, the model is highlighted; Record the highlighted model information and remove duplicate data. The highlighted tree model is the forest gap edge tree; The gap size measurement includes the following steps: Place the virtual camera above the forest window and adjust it to a bird's-eye view. Take the virtual camera position as the origin of the spatial coordinate system, send out collision rays in the opposite direction of the z-axis, and scan around the y-axis (0°, 90°) at intervals of σ degrees. When the collision ray collides with the canopy of the edge wood for the first time, the three-axis coordinates of the collision point are recorded and a coordinate point is generated. The coordinate point recorded at this time is the edge point of the forest window. Rotate clockwise (0°, 360°) around the z-axis at intervals of β degrees, repeat the above steps, and finally obtain all the forest gap edge points; Connect the marked points in sequence to generate polygons, and use the Shoelace Theorem formula to calculate the vertical projection area of ​​the forest gap; The forest gap shape measurement includes the following steps: According to the vertical projection coordinates of the generated forest gap edge marking points, connect the marking points and calculate the perimeter P, and use the shape index SI to represent the forest gap shape; The measurement of forest gap three-dimensional structure includes the following steps: Read the generated forest gap edge point spatial coordinates (x i ,y i , z i ), move the virtual camera to the same level as the forest gap edge and toward the forest gap edge point; The virtual camera descends at intervals of m meters until it is 1 meter above the ground. Each time it descends, it sends a collision ray to the edge of the forest window. When it collides with the edge tree, the coordinates of the collision point are recorded and a marker point P is generated. ij ; After generating a round of marking points, restore the virtual camera to the next forest window edge point P i+1 On the same horizontal plane, rotate β degrees clockwise around the z axis, and now it is heading towards the edge point P i+1 , repeat the above operation to generate a new round of marking points P i+1j ; Repeat the process for all forest gap edge points, and finally the total number of marker points generated is ((zi-1) / m))*(360 / β); i Instead of generating a marker point P ij Connect and connect the edge points of each forest gap to form a three-dimensional structure of the forest gap.

2. The method for measuring forest gap characteristics in a virtual forest scene according to claim 1, characterized in that: In step S3, The forest gap edge wood EdgeForestGap It is expressed as: T EdgeForestGap =f HighLigth (f Camera (x,H canopy ,y)) Among them, H canopy is the canopy height, n° is the rotation interval, f Camera Indicates the calculation of ray collision, f HighLigth Highlight the collision tree model, (x,H canopy ,y) represents the virtual camera coordinates.

3. The method for measuring forest gap characteristics in a virtual forest scene according to claim 2, characterized in that: In step S3, The area S of the forest gap size is expressed as: Among them, (x i ,y i ) is the vertical projection coordinate of the forest gap edge point i. In order to make all the marked points form a closed figure, the last marked point n is defined to be connected to the first point, and the x-axis coordinate of the first point in the calculation is defined as x n+1 Same as x1, y-axis coordinate y n+1 Same as y1, n is the total number of marked points.

4. The method for measuring forest gap characteristics in a virtual forest scene according to claim 3, characterized in that: In step S3, The forest gap perimeter P is expressed as: The shape index SI is expressed as: Where P is the perimeter of the forest gap, (x i ,y i ) is the vertical projection coordinate of the forest gap edge point i. In order to make all the marked points form a closed figure, the last marked point n is defined to be connected to the first point, and the x-axis coordinate of the first point in the calculation is defined as x n+1 Same as x1, y-axis coordinate y n+1 Same as y1, n is the number of marking points, and S is the forest gap area.

5. The method for measuring forest gap characteristics in a virtual forest scene according to claim 3, characterized in that: In step S3, The coordinates of the mark point i at the edge of the forest gap correspond to the mark point below ij : P ij =f Ray (x i ,y i ,z i -j×m) Among them, (x i ,y i , z i ) is the forest gap edge point P i Coordinate, j takes values ​​of (1, 2, 3, ..., (z i -1) / m), j×m is the camera descent height, f Ray (x i ,y i ,z i -j×m) indicates the calculation of the collision point coordinates, that is, the collision ray from the virtual camera (x i ,y i ,z i -j×m) coordinates, and the coordinates of the point where the camera collides with the 3D model of the tree.

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