A method for simulating the height at the maximum crown width in different directions of a three-dimensional tree model

Abstract

A method for simulating the height at the maximum crown width in different directions of a three-dimensional tree model, belonging to the technical field of three-dimensional modeling of tree polymorphism. Simulating the height at the maximum crown width of a tree includes steps of constructing a height model at the maximum crown width in a single direction and three-dimensional simulation of the height at the maximum crown width, and provides a three-dimensional model that conforms to the morphological laws of trees. The advantages of the present invention are: the implementation method is simple and effective, fully considering the influence of spatial competition in the forest stand on the height at the maximum crown width in different directions, and can realize the simulation of the height at the maximum crown width in different directions of trees in a virtual environment, and the simulation results meet the requirements of forestry applications.

Description

Technical Field

[0001] The present invention belongs to the technical field of three-dimensional modeling of tree polymorphism, and relates to a method for simulating the height at the maximum crown width in different directions of a three-dimensional tree model. Background Art

[0002] Three-dimensional modeling of tree polymorphism is a modeling process for parametrically expressing the outer contour morphology of trees, and its implementation is based on obtaining information on key position parameters of tree morphology. Among many key position parameters, the height at the maximum crown width is the height at the widest point in each direction of the crown, which is a very important position feature point in tree morphology, and its distribution is closely related to the growth and death process of tree branches. Moreover, each tree is affected by different spatial competition intensities in different directions, resulting in different distributions of the height at the maximum crown width in the corresponding directions. In a forest stand, the crown parts of trees overlap each other, making it difficult to measure and obtain the height at the maximum crown width, and it is difficult to guarantee the measurement accuracy. Therefore, the accurate simulation of the height at the maximum crown width is a difficulty and key point in three-dimensional modeling of tree polymorphism. Summary of the Invention

[0003] In view of the problems of the prior art, the present invention proposes a method for simulating the height at the maximum crown width in different directions of a three-dimensional tree model by constructing a height model at the maximum crown width and combining the existing trunk branching to load the three-dimensional modeling technology of tree polymorphism.

[0004] A method for simulating the height at the maximum crown width in different directions of a three-dimensional tree model includes the following steps: simulating the height at the maximum crown width of a tree, including the steps of constructing a height model at the maximum crown width in a single direction and three-dimensional simulation of the height at the maximum crown width, and providing a three-dimensional model that conforms to the morphological rules of trees.

[0005] The advantages of the present invention are: the implementation method is simple and effective, fully considering the influence of spatial competition in a forest stand on the height at the maximum crown width in different directions, and can simulate the height at the maximum crown width in different directions of a tree in a virtual environment, and the simulation results meet the requirements of forestry applications.

[0006] The implementation method is simple, fully considering the influence of different spatial competition intensities on the distribution of the height at the maximum crown width, constructing a height model at the maximum crown width in a single direction, and simulating the height at the maximum crown width in different directions; in the process of three-dimensional modeling of trees, it solves the problem of uniform distribution of the corresponding heights of the branches where the crown widths are located in different directions of the crown when constructing a three-dimensional tree model, and realizes the effect of differential expression of the height at the maximum crown width in different directions. Compared with the existing methods, the simulation results are closer to the real morphology of the crown in a forest stand, and the simulation results more conform to forestry laws and the requirements of forestry applications. Description of the Drawings

[0007] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings. As shown in the figures:

[0008] Figure 1 This is the overall technical flow chart of the present invention.

[0009] Figure 2 This is a schematic diagram of the height difference at the maximum crown width in different directions.

[0010] Figure 3 This is a schematic diagram for correcting the calculated value of the height at the maximum crown width.

[0011] Figure 4 This is a schematic diagram of the crown layer division.

[0012] Figure 5 This is a three-dimensional model diagram of the main trunk.

[0013] Figure 6 This is a three-dimensional model diagram of the branch.

[0014] Figure 7 This is a schematic diagram of the loading point of the branch model.

[0015] Figure 8 This is a schematic diagram for judging the distribution position of the three-dimensional branch model.

[0016] Figure 9 This is a schematic diagram of loading the three-dimensional branch model at the height of the maximum crown width.

[0017] Figure 10 This is a top view of Chinese fir within the spatial structure unit.

[0018] Figure 11 This is a front view of Chinese fir within the spatial structure unit.

[0019] Figure 12 This is a three-dimensional model diagram of Chinese fir No. 9.

[0020] Figure 13 This is a three-dimensional simulation diagram of a large-scale forest. Detailed implementation manners

[0021] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0022] Example 1: Figure 1 、 Figure 2 、 Figure 3 、 Figure 4 、 Figure 5 、 Figure 6 、 Figure 7 、 Figure 8 、 Figure 9 、 Figure 10 、 Figure 11 、 Figure 12 and Figure 13 As shown, a method for simulating the height of the maximum crown width of a tree in different directions of a three-dimensional model is provided. The method simulates the height of the maximum crown width of a tree, makes up for the problem that the current three-dimensional model of trees cannot simulate the height of the maximum crown width, provides technical support for simulating tree polymorphism, and provides a more realistic and more morphologically consistent three-dimensional model for intelligent forestry.

[0023] A method for simulating the height of a tree's three-dimensional model at its maximum crown width in different directions comprises the following steps:

[0024] Step 1: Constructing the height model of the maximum crown width in a single direction

[0025] The data collection and preprocessing steps include collecting tree height, crown width, height under branches, the height of the lowest and maximum crown width of trees in the four directions of east, west, south and north, and collecting the vertical spatial structure parameters and horizontal spatial structure parameters of each tree.

[0026] The height at maximum crown width is a characteristic parameter of crown morphology that changes with the growth and death of crown branches. Its distribution is directly related to the height of the tree and the spatial competition caused by surrounding trees. Therefore, the model was constructed using tree height and spatial structure parameters as variables.

[0027] Step 1.1: Construct the maximum crown height model based on the overall spatial structure unit

[0028] SPSS software was used for fitting. The model variables included vertical spatial structure parameters, horizontal spatial structure parameters, and tree height. In SPSS software, tree height, vertical spatial structure parameters, and horizontal spatial structure parameters were gradually introduced into the model as pre-selected variables for multivariate stepwise regression to construct a maximum crown height model based on the overall spatial structure unit.

[0029] After analysis and verification, the model is determined to be:

[0030] Hcr=a+b*H+c*PV+d*PH

[0031] Where Hcr is the height measurement value at the maximum crown width, H is the tree height, PV is the vertical spatial structure parameter within the spatial structure unit where the tree is located, PH is the horizontal spatial structure parameter within the spatial structure unit where the tree is located, and a, b, c, and d are model variable parameters.

[0032] Step 1.2 Discrimination of the Correlation between the Height at the Maximum Crown Width and the Spatial Structure Parameters

[0033] Unify the reference height of the height at the maximum crown width, conduct correlation analysis, and discriminate the association between the height at the maximum crown width and the spatial structure parameters.

[0034] The spatial competition intensity is different in different directions, resulting in different heights at the maximum crown width in different directions for each tree. To simulate the differences in the heights at the maximum crown width in different directions of the trees, it is necessary to judge the correlation between the spatial structure parameters and the height at the maximum crown width, and thus discriminate the specific direction among the four directions of east, west, south, and north where the measured value is located. The differences in the heights at the maximum crown width in different directions are as Figure 2 shown.

[0035] Figure 2 In, Hcrw is the height at the maximum crown width on the west side of the tree, and Hcre is the height at the maximum crown width on the east side of the tree.

[0036] As a height attribute, the tree height is directly related to the height at the maximum crown width. Therefore, before constructing the relationship between the height at the maximum crown width and the spatial structure parameters, it is first necessary to unify the reference height of the measured height at the maximum crown width to eliminate the influence of the tree height. The adjustment formula is:

[0037]

[0038] In the formula: Tp is the height adjustment parameter. Hmax is the maximum tree height in the sample plot, Hi is the tree height of each tree. Hcra is the height at the maximum crown width after unifying the reference height, and Hcr is the measured height at the maximum crown width.

[0039] Conduct correlation analysis on the height at the maximum crown width after unifying the reference and the spatial structure parameters, and allocate the measured height at the maximum crown width to the direction with the minimum spatial competition intensity according to the results. The formula for calculating the spatial competition intensity is:

[0040] SPC = Rcv * SPV + Rch * SPH

[0041] In the formula: SPC is the spatial competition intensity in a single direction, Rcv is the correlation coefficient between the height at the maximum crown width after unifying the reference and the vertical spatial structure parameter, SPV is the vertical spatial structure parameter in a single direction, Rch is the correlation coefficient between the height at the maximum crown width after unifying the reference and the horizontal spatial structure parameter, and SPH is the horizontal spatial structure parameter in a single direction.

[0042] Step 1.3 Construction of the Model for the Height at the Maximum Crown Width in a Single Direction

[0043] Fit with SPSS software, and the model variables include the vertical spatial structure parameter in a single direction, the horizontal spatial structure parameter in a single direction, and the tree height.

[0044] Calculate the vertical and horizontal spatial structure parameters in the four directions of east, west, south, and north respectively. In SPSS, fit the height model at the maximum crown width in a single direction with the vertical and horizontal spatial structure parameters and tree height in the direction of the minimum spatial competition intensity. The model is:

[0045] SHcr = a1 + b1 * H + c1 * SPV + d1SPH

[0046] In the formula, SHcr is the height at the maximum crown width corresponding to the vertical spatial structure parameter in a single direction, H is the tree height, SPV is the vertical spatial structure parameter in a single direction, SPH is the horizontal spatial structure parameter in a single direction, and a1, b1, c1, and d1 are the model variable parameters.

[0047] So far, the process of constructing the height model at the maximum crown width in a single direction is completed, and three-dimensional expression is carried out with this as a parameter.

[0048] Step 2 Three-dimensional simulation of the height at the maximum crown width:

[0049] Calculate and correct the height at the maximum crown width (compare the calculated values with the measured values in other directions except the measured direction). After obtaining the height model at the maximum crown width in a single direction, the height at the maximum crown width in each direction can be calculated. At this time, there are two situations.

[0050] (1) When the calculated values of the height at the maximum crown width in the remaining directions are all greater than the measured values except for the direction of the measured maximum crown width distribution to be discriminated;

[0051] (2) In addition to the discriminated direction, there are other directions where the calculated values are less than the measured values.

[0052] In the first case, directly use the measured values and the calculated values in the remaining directions as parameters to construct a three-dimensional model, and use the calculated values as the height at the maximum crown width in the corresponding directions.

[0053] In the second case, the calculated values need to be corrected. Correct the calculated values in the other three directions through the difference between the calculated value and the measured value in the measured direction.

[0054] Step 2.1 Correction of the calculated value of the height at the maximum crown width

[0055] When, in addition to the discriminated direction, there are other directions where the calculated values are less than the measured values, construct a correction coefficient for the height at the maximum crown width to adjust the calculated values in the remaining directions. The adjustment formula is:

[0056]

[0057] Where: TPc is the difference between the measured direction measurement value and the calculated value as the correction parameter, Hcrm is the measured height value at the maximum crown width of the measured direction, Hcre is the calculated height value at the maximum crown width of the measured direction, Hcpa is the corrected height at the maximum crown width in other directions except the measured direction, and Hcp is the calculated value of the height at the maximum crown width in other directions except the measured direction.

[0058] The adjustment situation is as Figure 3 shown.

[0059] Figure 3 The position of the ellipse in the figure is the corrected height at the maximum crown width.

[0060] Step 2.2 Judgment and loading of the distribution position of the three-dimensional model of the branches corresponding to the height at the maximum crown width

[0061] The tree crown is divided into upper, middle and lower layers according to the branch elevation angle. The branch angle corresponding to the height at the maximum crown width is set between 80° and 85°. The probability of the branch elevation angle appearing in each layer conforms to the normal distribution. The elevation angle of the first-level branches in the lower layer is set to 70° - 90°; the middle layer is 50° - 70°; the upper layer is 30° - 50°. This is used as the distribution range of the branch elevation angles at different positions.

[0062] As Figure 4 shown. The three-dimensional model of the main trunk is as Figure 5 shown. The three-dimensional model of the branches is as Figure 6 shown.

[0063] At the four directions of east, west, south and north of the main trunk, branch model loading points are generated starting from the position of the height below the branches. According to the number of tree branch growth rounds and the spacing between branches, loading points are generated one by one towards the top of the tree as the initial identification of the branch model loading positions. The constructed branch model loading points are as Figure 7 shown.

[0064] The demarcation point between the middle layer and the lower layer is the crown width. Therefore, this position corresponds to the height at the maximum crown width, and the corresponding branch three-dimensional model loading point is in the lower layer area. Since the branch corresponding to the crown width height is the longest branch, and generally it is not the lowest branch of the forest tree, therefore, according to the branch elevation angle distribution law and considering the influence of the branch length on the branch elevation angle, its branch elevation angle is set between 80° and 85°.

[0065] For the lower layer area, starting from the highest loading point, make a judgment downwards. Make a ray at an elevation angle from 80° to 85°. If the intersection point with the outer contour of the tree crown is in the lower layer area, then load the branch model with the angle of the line connecting this loading point and the point at the height of the maximum crown width on the outer contour; if the intersection point is in the middle layer area, then delete this loading point and make a judgment on the next loading point until the condition is met. Then, starting from the topmost point of the lower layer of the tree crown, select the highest point where the branches are completely distributed in the lower layer as the corresponding branch loading position and load the three-dimensional model of the branches. AsFigure 8 as shown

[0066] Load the branched three-dimensional model according to the judgment position to achieve the three-dimensional simulation of the height at the maximum crown width. The loaded branched three-dimensional model is as Figure 9 shown

[0067] Thus, the entire process of simulating the height at the maximum crown width in different directions of the tree three-dimensional model is completed.

[0068] Example 2: As Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 7 , Figure 8 , Figure 9 , Figure 10 , Figure 11 , Figure 12 and Figure 13 shown, a method for simulating the height at the maximum crown width in different directions of a tree three-dimensional model

[0069] Example of Simulating the Height at the Maximum Crown Width in Different Directions of the Chinese Fir Three-Dimensional Model in the Lower Mountain Forest Farm of the Jiangxi Academy of Forestry

[0070] 1. Data collection

[0071] Taking 239 Chinese fir trees in 8 plots of 20m * 20m in the lower mountain forest farm of the Jiangxi Academy of Forestry as an example, measure the relative position coordinates (X, Y, Z) of each tree in the plot, and measure the parameters such as the diameter at breast height, tree height, and height at the maximum crown width of the trees in the plot. The basic measurement data of Chinese fir in the plot are shown in Table 1:

[0072] Table 1 Basic Measurement Data of Chinese Fir in the Plot

[0073] Type Tree height (m) Diameter at breast height (cm) Height under branches (m) Height at maximum crown width (m) Crown width (m) Maximum value 30.4 36.5 14.6 18.1 4.0 Minimum value 8.8 8.3 4.5 7.2 0.4 Average value 17.8 23.6 8.0 13.9 1.7

[0074] Calculate the overall vertical spatial structure parameters, horizontal spatial structure parameters of the spatial structure unit, and the spatial structure parameters of each tree in the east, west, south, and north directions.

[0075] 2. Fitting of the height model at the maximum crown width

[0076] Divide the data into a modeling group and a verification group according to 4:1. First, use the SPSS statistical software to construct a maximum crown width height model based on the overall spatial structure unit through multiple stepwise regression, and perform regression analysis on the crown width height, tree height (H), overall horizontal spatial structure parameter (PH), and overall vertical spatial structure parameter (PV). The model fitting results are shown in Table 2.

[0077] Table 2 Model Fitting Results

[0078]

[0079] The goodness-of-fit model parameters are shown in Table 3 as follows:

[0080] Table 3 Model statistics

[0081]

[0082] It can be seen that the height model at the maximum crown width based on the overall spatial structure unit is:

[0083] IIcr - 0.469 + 0.621×II + 1.432×PV + 0.837×PII

[0084] Using the validation group data for testing, the test results are shown in Table 4 as follows:

[0085] Table 4 Test results of the height model at the maximum crown width based on the overall spatial structure unit

[0086] Average of measured values (m) Average of calculated values (m) t - test value P - value 10.91 11.53 1.64 0.108

[0087] It can be seen that the calculated value is slightly larger than the measured value, and the P value > 0.05, indicating that there is no significant difference between the two, and the model can be used to predict the height at the maximum crown width.

[0088] Unify the reference height of the height at the maximum crown width of each tree, and analyze the correlation with the vertical spatial structure parameters and horizontal spatial structure parameters within the spatial structure unit. The correlation with the vertical spatial structure parameters is 0.621; the correlation with the horizontal spatial structure parameters is 0.583. Both show a significant positive correlation, indicating that the height at the maximum crown width will increase with the increase of the spatial competition intensity. Therefore, the measured values are distributed in the direction with the minimum spatial competition intensity. The calculation formula for the spatial competition intensity is determined as:

[0089] SPC = 0.621*SPV + 0.583*SPH

[0090] Calculate the direction of the minimum spatial competition intensity of each tree, and use the vertical spatial structure parameters and horizontal spatial structure parameters in this direction as variables to fit the model again, and obtain the height model at the maximum crown width in a single direction:

[0091] SHcr = 1.352 + 0.572×H + 1.753×SPV + 0.771×SPH

[0092] Conduct model testing again, and the model fitting results are shown in Table 5 as follows:

[0093] Table 5 Fitting results of the height model at the maximum crown width in a single direction

[0094] Coefficient of determination Adjusted coefficient of determination Standard deviation of the estimate 0.768 0.762 1.458

[0095] Compared with the fitting results of Model 4 in Table 2, it can be seen that the goodness of fit has improved, which further proves that the measured values can be distributed in the direction with the minimum spatial competition intensity.

[0096] 3. Three-dimensional simulation of the height at the maximum crown width

[0097] For each tree, judge whether the calculated value needs to be corrected. For those that need to be corrected, adjust them according to the correction formula, and load the three-dimensional branch model on the three-dimensional trunk model according to the adjusted position to achieve the three-dimensional simulation of the height at the maximum crown width.

[0098] The top view shown in a spatial structure unit is as Figure 10 shown, and the front view is as shown in 11.

[0099] In the figure, Chinese fir No. 9 is the central tree of this spatial structure unit. The measured data of Chinese fir No. 9 are: diameter at breast height 13.7 cm, tree height 16.5 m, measured height at the maximum crown width 11.3 m, height under branches 7.8 m, and crown widths in the east, west, south, and north directions are 1.7 m, 1.5 m, 1.2 m, and 1.5 m respectively. Build its spatial structure unit, and the surrounding trees are determined as: Chinese fir No. 18 and No. 22 on the east side, Chinese fir No. 3 on the west side, Chinese fir No. 17 on the south side, and Chinese fir No. 4 and No. 5 on the north side. After calculation, the spatial competition intensity on the south side is the smallest, and the measured value is assigned to the south side. The calculation results of the height at the maximum crown width in the east, west, south, and north directions are: 11.858 m, 12.788 m, 11.342 m, and 12.909 m respectively. After retaining one decimal place, the results are 11.9 m, 12.8 m, 11.3 m, and 12.9 m. It can be seen that on the south side where the calculated value is the smallest, it is the same as the measured value after retaining one decimal place, and the calculated values in the other directions are all greater than the measured value, which can be directly used as modeling parameters for model construction. Chinese fir No. 9 is observed from the east-west and north-south directions as Figure 12 shown. Applying the present invention to large-scale forest three-dimensional simulation is as Figure 13 shown. From the simulation results, it can be seen that the simulation results of the height at the maximum crown width in different directions of the tree three-dimensional model can effectively simulate the morphological characteristics of the tree crown and meet the application requirements of forest visualization simulation research.

[0100] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for simulating the height at the maximum crown width in different directions of a three-dimensional tree model, characterized in that, It includes the following steps: simulating the height at the maximum crown width of a tree, including the steps of constructing a model for the height at the maximum crown width in a single direction and three-dimensional simulation of the height at the maximum crown width, providing a three-dimensional model that conforms to the morphological laws of trees, and constructing a model for the height at the maximum crown width in a single direction, which includes the following steps: The data collection and preprocessing steps include collecting the tree height, crown width, height below branches, and the lowest height at the maximum crown width in the four directions of east, west, south, and north of the tree, and collecting the vertical spatial structure parameters and horizontal spatial structure parameters of each tree. Step 1.1 Construction of the model for the height at the maximum crown width based on the overall spatial structure unit Fitting with SPSS software, the model variables include vertical spatial structure parameters, horizontal spatial structure parameters, and tree height. In SPSS software, the tree height, vertical spatial structure parameters, and horizontal spatial structure parameters are used as preselected variables and gradually brought into the model for multiple stepwise regression to construct a model for the height at the maximum crown width based on the overall spatial structure unit. The determined model is:[[]] Hcr = a + b*H + c*PV + d*PH In the formula, Hcr is the measured value of the height at the maximum crown width, H is the tree height, PV is the vertical spatial structure parameter within the spatial structure unit where the tree is located, PH is the horizontal spatial structure parameter within the spatial structure unit where the tree is located, and a, b, c, and d are model variable parameters. Step 1.2 Discrimination of the correlation between the height at the maximum crown width and spatial structure parameters Unify the reference height of the height at the maximum crown width, conduct a correlation analysis, and discriminate the association between the height at the maximum crown width and spatial structure parameters. Hcrw is the height at the maximum crown width on the west side of the tree, and Hcre is the height at the maximum crown width on the east side of the tree. As a height attribute, the tree height is directly related to the height at the maximum crown width. Therefore, before constructing the relationship between the height at the maximum crown width and spatial structure parameters, it is first necessary to unify the reference height of the measured height at the maximum crown width to eliminate the influence of the tree height. The adjusted formula is: In the formula: Tp is the height adjustment parameter, Hmax is the maximum tree height in the plot, Hi is the tree height of each tree, Hcra is the height at the maximum crown width after unifying the reference height, and Hcr is the measured height at the maximum crown width. Conduct a correlation analysis on the height at the maximum crown width after unifying the reference and spatial structure parameters, and allocate the measured height at the maximum crown width to the direction with the minimum spatial competition intensity according to the results. The formula for calculating the spatial competition intensity is: SPC = Rcv*SPV + Rch*SPH In the formula: SPC is the spatial competition intensity in a single direction, Rcv is the correlation coefficient between the height at the maximum crown width after unifying the reference and the vertical spatial structure parameter, SPV is the vertical spatial structure parameter in a single direction, Rch is the correlation coefficient between the height at the maximum crown width after unifying the reference and the horizontal spatial structure parameter, and SPH is the horizontal spatial structure parameter in a single direction. Step 1.3 Construction of the model for the height at the maximum crown width in a single direction Fitted by SPSS software, the model variables include the vertical spatial structure parameters in a single direction, the horizontal spatial structure parameters in a single direction, and tree height. Calculate the vertical spatial structure parameters and horizontal spatial structure parameters in the four directions of east, west, south, and north. In SPSS, fit the height model at the maximum crown width in a single direction with the vertical spatial structure parameters, horizontal spatial structure parameters, and tree height in the direction of the minimum spatial competition intensity. The model is: SHcr = a1 + b1*H + c1*SPV + d1*SPH In the formula, SHcr is the height at the maximum crown width corresponding to the vertical spatial structure parameter in a single direction, H is the tree height, SPV is the vertical spatial structure parameter in a single direction, SPH is the horizontal spatial structure parameter in a single direction, and a1, b1, c1, d1 are the model variable parameters.

2. The method for simulating the height at the maximum crown width in different directions of a three-dimensional model of a tree according to claim 1, characterized in that, The three-dimensional simulation of the height at the maximum crown width includes the following steps: Calculate and correct the height at the maximum crown width. After obtaining the height model at the maximum crown width in a single direction Calculate the height at the maximum crown width in each direction. At this time, there are two cases (1) Except for the direction where the measured height distribution at the maximum crown width is discriminated, the calculated values of the height at the maximum crown width in the other directions are all greater than the measured values; (2) In addition to the discriminated direction, there are other directions where the calculated values are less than the measured values. For the first case, directly use the measured values and the calculated values in the other directions as parameters to construct a three-dimensional model, and use the calculated values as the height at the maximum crown width in the corresponding directions. For the second case, the calculated values need to be corrected. Correct the calculated values in the other three directions through the difference between the calculated value and the measured value in the measured direction. Step 2.1 Correction of the calculated value of the height at the maximum crown width If the calculated value in the discriminated direction or other directions is less than the measured value, construct a correction coefficient for the height at the maximum crown width and adjust the calculated values in the remaining directions. The adjustment formula is: In the formula: TPc is the difference between the measured value and the calculated value in the determined measured direction as the correction parameter, Hcrm is the measured value of the height at the maximum crown width in the determined measured direction, Hcre is the calculated value of the height at the maximum crown width in the determined measured direction, Hcpa is the corrected height at the maximum crown width in the other directions except the measured direction, and Hcp is the calculated value of the height at the maximum crown width in the other directions except the measured direction. Step 2.2 Judgment and loading of the distribution position of the three-dimensional model of the branches corresponding to the height at the maximum crown width Divide the tree crown into upper, middle, and lower layers according to the branch elevation angle. The branch angle corresponding to the height at the maximum crown width is set between 80° and 85°. The probability of the branch elevation angle appearing in each layer conforms to a normal distribution. The elevation angle of the first-level branches in the lower layer is set between 70° and 90°; the middle layer is between 50° and 70°; the upper layer is between 30° and 50°. Use this as the distribution range of the branch elevation angles at different positions. Generate branch model loading points starting from the position of the under-branch height in the four directions of the main trunk, east, west, south, and north. According to the number of tree branch growth rings and the spacing between branches, generate loading points one by one towards the top of the tree as the initial identifier of the branch model loading position. The demarcation point between the middle layer and the lower layer is the crown width. Therefore, this position corresponds to the height at the maximum crown width, and the corresponding branch three-dimensional model loading point is in the lower layer area. Since the branch corresponding to the crown width height is the longest branch, not the lowest branch of the forest tree, according to the distribution law of the branch elevation angle and considering the influence of the branch length on the branch elevation angle, set its branch elevation angle between 80° and 85°. For the lower layer area, start judging downward from the highest loading point, draw a ray at an elevation angle of 80° to 85°. If the intersection point with the outer contour of the tree crown is in the lower layer area, load the branch model at the angle of the line connecting the loading point and the height point at the maximum crown width on the outer contour; If the intersection point is in the middle layer area, delete the loading point and judge the next loading point until the condition is met. Then start judging from the topmost point of the lower layer of the tree crown, select the highest point where the branches are completely distributed in the lower layer as the corresponding branch loading position, and load the 3D branch model. Load the 3D branch model according to the judged position to achieve the 3D simulation of the height at the maximum crown width. Thus, the entire process of simulating the height at the maximum crown width in different directions of the tree 3D model is completed.

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