A visual simulation method for tree crown growth based on illumination model

Abstract

A method for visualizing and simulating tree crown growth based on an illumination model belongs to the field of forestry informatization. Based on a three-dimensional tree model constructed using periodic B-spline curves, the method combines the tree growth model to study the relationship between tree crown changes in previous and subsequent years and the canopy light distribution in the current year. A tree crown-light coupling model is constructed to achieve visual simulation of tree crown morphology based on the illumination model. The illumination model-based visualization simulation method for fir tree crown morphology is simple and effective, fully considering the impact of the lighting environment on crown morphology. It can realize dynamic changes in crown morphology, and its accuracy fully meets the requirements of grassroots forestry applications.

Description

Technical Field

[0001] The invention belongs to the field of forestry informatization and relates to a tree crown growth visualization simulation method based on a light model. Background Art

[0002] Tree crown shape refers to the overall form of a tree's crown. Crown shape curves are typically used to describe tree crown shapes in different directions. This is a key indicator of crown morphological diversity. Tree crown morphology is polymorphic, driven by numerous factors. In addition to the tree's own genetics, the growth environment is also crucial. However, measuring crown shape is difficult and costly. Therefore, studying the relationship between crown shape and its growth environment, and thus predicting its growth and changes, is a key area of ​​forestry research.

[0003] Numerous environmental factors influence forest morphology and structure. At the plot scale, due to the small spatial span, factors such as temperature, soil, air, altitude, and moisture within the same plot are not significantly different. Therefore, at the plot scale, these factors have roughly the same impact on forest morphology and structure. However, within the same plot, canopy illumination varies significantly, arguably being the primary factor contributing to the "diverse appearances" of trees. Therefore, visual simulations of the interaction between forest morphology and the environment can focus on the impact of canopy illumination distribution on crown morphology, building on growth models.

[0004] Illumination models, also known as chiaroscuro models, are a crucial area of ​​computer graphics research. When light strikes an object's surface in reality, it undergoes physical phenomena such as reflection, refraction, absorption, transmission, and interference. When this reflected and refracted light enters the human visual system, it allows the object to be seen. To simulate this physical phenomenon, where light strikes an object and then reflects back to the human eye, allowing the object to be seen, researchers have constructed mathematical models to replace the complex physical models of real life. Illumination models can be used in research to study the distribution of light within a forest canopy. Ray tracing algorithms and radiosity models are currently the most commonly used. Summary of the Invention

[0005] The present invention solves the technical problems existing in the prior art, thereby providing a method for visual simulation of tree crown growth based on a lighting model.

[0006] The existing technical problems are solved by the following technical solutions: a method for visual simulation of tree crown growth based on an illumination model, comprising the following steps: on the basis of a three-dimensional tree model constructed using a periodic B-spline curve, combined with the tree growth model, studying the relationship between the crown changes of trees in previous and subsequent years and the light distribution of the tree canopy in that year, constructing a tree crown-light coupling model, and realizing visual simulation of tree crown morphology based on the illumination model.

[0007] The advantages of the present invention are that the method for visual simulation of Chinese fir crown morphology based on the illumination model is simple and effective to implement, fully considers the influence of the illumination environment on the crown morphology, can realize dynamic changes in the crown morphology, and its accuracy fully meets the application requirements of grassroots forestry. On the basis of the illumination model, the influence of the illumination environment on the crown shape changes during the growth of trees is considered, which makes up for the defect that the changes in the crown shape of trees in the current visualization simulation of tree growth only consider the influence of a few characteristic points such as tree height and crown width, and cannot accurately express the changes in crown shape. It more accurately expresses the changes in crown shape during the growth of trees, thereby providing more accurate three-dimensional simulation of trees for subsequent forestry planning. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work. As shown in the figure:

[0009] Figure 1 This is a flow chart of the fir crown-light coupling model of the present invention.

[0010] Figure 2 This is a flowchart of the crown morphology simulation based on the fir crown-light coupling model of the present invention.

[0011] Figure 3 This is a calculation diagram of the photosynthetically active radiation distribution of the Chinese fir tree canopy according to the present invention.

[0012] Figure 4a This is a comparison diagram of the B_CMD fir crown curve of the present invention.

[0013] Figure 4b This is a comparison diagram of the CMD_N fir crown curve of the present invention.

[0014] Figure 4c This is a comparison diagram of the CMD fir crown curve of the present invention.

[0015] Figure 4d This is a comparison diagram of the CMD_CCLM fir crown curve of the present invention.

[0016] Figure 5a This is a forest stand scene before growth of the Chinese fir crown morphology visualization simulation based on the illumination model of the present invention.

[0017] Figure 5b This is a forest stand scene after growth of the Chinese fir crown morphology visualization simulation based on the illumination model of the present invention. DETAILED DESCRIPTION

[0018] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0019] Example 1: Figure 1 、 Figure 2 、 Figure 3 、 Figure 4a 、 Figure 4b 、 Figure 4c 、 Figure 4d 、 Figure 5a and Figure 5b This paper presents a method for visualizing tree crown growth based on an illumination model. This method considers the influence of the lighting environment on crown shape changes during tree growth, overcoming the drawback of current visualizations of tree growth, which only consider the influence of a few characteristic points, such as tree height and crown width, and fail to accurately represent crown shape changes. This method more accurately depicts crown shape changes during tree growth, thus providing more accurate three-dimensional simulations for subsequent forestry planning.

[0020] The present invention mainly studies the relationship between the crown shape changes of trees in previous and subsequent years and the canopy light distribution of trees in this year based on the three-dimensional forest model constructed using periodic B-spline curves, combines the forest growth model, constructs a forest crown-light coupling model, and realizes the visualization simulation technology of forest crown morphology based on the light model.

[0021] Specific steps:

[0022] Step 1: Construction of the Chinese fir crown-light coupling model

[0023] Step 1.1. Obtain the base period Chinese fir crown shape data (data of each crown shape measurement point) from the sample site survey, which is represented by a set of (i, d, h, w), which can represent the crown width (width w) at the corresponding Chinese fir (number i), corresponding direction (direction d), and corresponding height (height h).

[0024] Step 1.2: Construct a crown curve for Chinese fir trees using a set of (h, w) as the base points of a periodic B-spline curve. This yields the crown curves for each Chinese fir tree in the four directions of east, south, west, and north. A three-dimensional Chinese fir model is then constructed using the crown curves in these four directions. A three-dimensional scene of the Chinese fir stand is then constructed, combining the terrain data and the spatial location data of the Chinese fir trees. A ray tracing algorithm is then used within the three-dimensional Chinese fir stand scene, using the annual average photosynthetically active radiation as the illumination parameter to calculate the light intensity at the Chinese fir crown measurement points. This results in the Chinese fir canopy light distribution data (LDD), represented as a set of (i, d, h, I) data representing the light intensity (light intensity I) at the corresponding Chinese fir tree (number i), direction (direction d), and height (height h), corresponding to the baseline Chinese fir crown data (i, d, h, w).

[0025] Step 1.3: Baseline Chinese fir attribute data were also obtained from the plot survey and are expressed as (i, D, H), where i represents the Chinese fir tree number, D represents the diameter at breast height (DBH), and H represents the tree height. Combining the DBH growth model with the tree height-DBH curve model yields simulated current Chinese fir attribute data (i, D′, H′) without light effects, and simulated current Chinese fir crown shape data (CMD_N(i, d, h′, w′) without light effects. In the DBH growth model and the tree height-DBH curve model, PD represents relative plant distance, PA represents relative dominance, D represents DBH, and PI represents position index, reflecting the overall environmental conditions. The crown morphology of the baseline Chinese fir crown shape data and the simulated current Chinese fir crown shape data without light effects did not change; only the proportions varied.

[0026] Step 1.4: Construct a Chinese fir crown curve using field survey data. The current crown data (CMD(i, d, h′, w)) of the Chinese fir trees in the sample plot were obtained from the crown curve. The relationship between the light distribution data, the current crown data, and the simulated current Chinese fir crown data without light effects was investigated. Finally, a statistical method was used to construct a coupled crown-light model for Chinese fir (Equation 1), where CMD represents the current crown data, CMD_N represents the simulated current Chinese fir crown data without light effects, LDD represents the light distribution data, a represents the intercept, and b and c represent the coefficients.

[0027] CMD=a+b*CMD_N+c*LDD (1)

[0028] Step 2: Crown morphology simulation based on the Chinese fir crown-light coupling model

[0029] Step 2.1: Combine the base period Chinese fir attribute data and base period Chinese fir crown shape data with the diameter at breast height growth model and the tree height-curve model to obtain the current period Chinese fir crown shape simulation data CMD_N without considering the influence of light.

[0030] Step 2.2: The canopy light distribution data LDD of Chinese fir and the current crown shape simulation data CMD_N of Chinese fir without considering the influence of light are brought into the constructed crown-light coupling model to obtain the crown shape data that considers the influence of light factors on the crown shape of Chinese fir, that is, the crown shape simulation data CMD_CCLM is obtained based on the Chinese fir crown-light model.

[0031] Step 2.3: Current Chinese fir crown shape data (CMD) is obtained from the plot survey. Both CMD and CMD_CCLM are crown shape data, represented by a set (i, d, h, w). The similarity between two sets of crown shapes is measured using the Euclidean distance of the crown shape data.

[0032] Step 2.4: Calculate the Euclidean distance D_CCLM between CMD and CMD_CCLM. The smaller the Euclidean distance, the better the fitting effect.

[0033] Example 2: Figure 1 、 Figure 2 、 Figure 3 、 Figure 4a 、 Figure 4b 、 Figure 4c 、 Figure 4d 、 Figure 5a and Figure 5b As shown in the figure, a visualization simulation method for tree crown growth based on illumination model is used, and an example of visualization simulation research on the interaction between the morphological structure and environment of Chinese fir in Huangfengqiao State Forest Farm, Hunan Province is given.

[0034] 1. Data Collection Steps

[0035] A typical 40m x 40m plot was selected within the Huangfengqiao Forest Farm, housing 230 Chinese fir trees. Orthophotos from unmanned aerial vehicles (UAVs) were used to obtain spatial information on the plot's topographic elevation. A total station was used to obtain the relative (X, Y) coordinates of the Chinese fir tree trunks and roots, representing their distribution within the plot. From 2015 to 2017, a conventional field survey was conducted on the Chinese fir trees within the plot. Crown descriptors such as tree height, crown width, height at maximum crown width, and height under active branches were obtained in four directions (east, south, west, and north). Crown width was also measured at meter intervals in each of the four directions. Global long-sequence, high-resolution photosynthetically active radiation (PAR) data were also obtained from the National Tibetan Plateau Data Center.

[0036] 2. Calculation steps for PAR (Parity Index) of Chinese fir tree crowns based on a ray tracing algorithm. The annual average PAR in You County, Hunan Province, in 2015 and 2016 was 119.13 and 121.62 W / m2, respectively. The diurnal variation in PAR exhibits a single peak, gradually rising in the morning and reaching its daily peak around noon, then gradually declining. Combining the annual average PAR and the diurnal PAR variation curve, the annual average values ​​for the seven corresponding moments were estimated. Using a ray tracing algorithm, the PAR intensity at each measurement point at the seven moments was calculated and summed to represent the PAR intensity at that point. Measurements were taken at one-meter intervals along the crown of each Chinese fir tree in the four directions of east, south, west, and north, and the LDD (Low Length Divided) PAR intensity at each measurement point was calculated for two years.

[0037] 3. Steps for constructing the Chinese fir canopy illumination coupling model

[0038] The 2015 survey data were used as the base period for Chinese fir crown shape data, and the 2016 survey data were used as the current period for Chinese fir crown shape data (CMD). The light distribution data (LDD) at this time was the calculated distribution of photosynthetically active radiation in the Chinese fir canopy in 2015. Based on this, the DBH growth model and the tree height-curve model were combined to obtain the current period simulated Chinese fir crown shape data (CMD_N) without considering the influence of light.

[0039] CMD describes the crown shape of Chinese fir trees measured in 2016; CMD_N describes the crown shape of Chinese fir trees in 2016 simulated using the diameter-at-breast-height growth model and the tree height-curve model, which indirectly reflects the age factor. Each measurement point has a corresponding height, but because the crown width of different Chinese fir trees at the same height may vary, the height of the measurement point is not used as a model parameter. Using the multivariate stepwise regression method, CMD, CMD_N, and LDD were regressed in SPSS software. Ultimately, the analysis determined that the crown-light coupling model for Chinese fir trees is as shown in Equation 2:

[0040] CMD=-40.419+0.927*CMD_N+0.012LDD (2)

[0041] 4. Crown morphology simulation steps based on the Chinese fir crown-light coupling model

[0042] The model was validated using survey data from 2016 and 2017. The 2016 survey data served as the base crown data (B_CMD), and the 2017 survey data served as the current crown data (CMD). The light distribution data (LDD) was the calculated photosynthetically active radiation distribution of the Chinese fir canopy in 2016. Combining the Chinese fir diameter at breast height (DBH) growth model with the height-DBH curve model yielded the current simulated Chinese fir crown data (CMD_N) without the influence of light. LDD and CMD_N were then incorporated into the Chinese fir crown-light coupling model to obtain the current simulated Chinese fir crown data (CMD_CCLM) simulated using the Chinese fir crown-light coupling model. The Euclidean distance (D_CCLM) between CMDD_CCLM and CMD was calculated to be 15.561.

[0043] The height range of Chinese fir trees in the plot is 9.1-18.5m. A Chinese fir tree was randomly selected to construct the crown curve of the Chinese fir tree based on CMD_CCLM and CMD. Figure 4a 、 Figure 4b 、 Figure 4c 、 Figure 4d As shown in the figure, the crown shape of the Chinese fir tree in the base period, B_CMD, and the crown shape data without light factors, CMD_N, are the same, showing a proportional relationship. Compared with the current period data, CMD, the crown shape simulated using the crown-light coupling model has a higher degree of fit than the crown shape without light factors.

[0044] The three-dimensional forest stand scene was constructed using the plot survey data. The growth simulation was carried out in combination with the fir canopy-light coupling model in the three-dimensional scene. The simulation results are shown in Figure 2. Figure 5a and Figure 5b shown.

[0045] Example 3: Figure 1 、 Figure 2 、 Figure 3 、 Figure 4a 、 Figure 4b 、 Figure 4c 、 Figure 4d 、 Figure 5a and Figure 5b As shown in the figure, a visualization simulation method of tree crown growth based on illumination model is proposed.

[0046] Step 1: Construct a 3D model of the Chinese fir stand

[0047] The first step in building a Chinese fir canopy-light coupling model is to construct a three-dimensional scene of the Chinese fir forest stand.

[0048] Step 1.1 Build a 3D model of the fir tree:

[0049] The crown shape data (i, d, h, w) of Chinese fir in the base period are used as the type value points Qi (i=0, 1, 2,…, n), (h, w) of the crown shape curve. The crown shape curve of Chinese fir is fitted by a periodic B-spline curve, and the crown shape curve is used as the constraint condition of the crown outer contour to construct a three-dimensional model of Chinese fir.

[0050] Step 1.2: Construct a 3D scene of the Chinese fir forest:

[0051] Through the terrain data and the spatial position data of the Chinese fir, the constructed three-dimensional Chinese fir model is loaded into the corresponding position to construct a three-dimensional scene of the Chinese fir forest. At this time, the three-dimensional Chinese fir model corresponding to each position has real crown parameters.

[0052] Step 2: Fir tree canopy-light coupling model

[0053] Through the crown shape data and attribute data (i, D, H) of the base period Chinese fir, combined with the DBH growth model and the tree height-DBH curve model,

[0054] d D / dt=1.564RD 0.515 RA 0.027 (0.133SI 0.886 D 0.230 -0.016SI 0.733 D)

[0055] H=0.492SI 0.531 D 2 / 3

[0056] Where dD / dt represents the ratio of the change in DBH to the change in time, RD represents the relative plant distance, RA represents the relative dominance, D represents the DBH, SI represents the status index, and H represents the tree height.

[0057] Simulate the crown shape parameters CMD_N(i, d, h′, w′) of the current Chinese fir tree without the influence of light. In this case, the crown shape before and after growth only changes in size, and the overall shape does not change:

[0058]

[0059] Where: H is the tree height, H' is the tree height without lighting fitting, h is a certain height on the crown, h' is a certain height on the crown of the tree without lighting fitting, w is the crown width at the corresponding height (height h), and w' is the crown width at the corresponding height (height h') on the crown of the tree without lighting fitting.

[0060] The ray tracing algorithm is used to calculate the annual average photosynthetically active radiation and the three-dimensional scene of the Chinese fir forest canopy light distribution data LDD(i, d, h, I). The Chinese fir crown-light coupling model is constructed with the current Chinese fir crown parameters without adding light effects. The current Chinese fir crown data is CMD(i, d, h′, w), and the fitting model form is:

[0061] CMD=Intercept+b*CMD_N+c*LDD

[0062] Where: CMD is the current crown shape data of Chinese fir, Intercept is a constant, b and c are coefficients, CMD_N is the current crown shape simulation data of Chinese fir without considering the influence of light, and LDD is the light distribution data of Chinese fir canopy.

[0063] This completes the construction of the fir crown-light coupling model.

[0064] Example 4: Figure 1 、 Figure 2 、 Figure 3 、 Figure 4a 、 Figure 4b 、 Figure 4c 、 Figure 4d 、 Figure 5a and Figure 5b As shown in the figure, a visualization simulation method of tree crown growth based on illumination model is proposed.

[0065] Step 1: Simulation of current fir crown shape without considering the effect of sunlight

[0066] Through the base period Chinese fir crown shape data (i, d, h, w) and base period Chinese fir attribute data (i, D, H), combined with the DBH growth model and tree height-DBH curve model

[0067] d D / dt=1.564RD 0.515 RA 0.027 (0.133SI 0.886 D 0.230 -0.016SI 0.733 D)

[0068] H=0.492SI 0.531 D 2 / 3

[0069] Where dD / dt represents the ratio of the change in DBH to the change in time, RD represents the relative plant distance, RA represents the relative dominance, D represents the DBH, SI represents the status index, and H represents the tree height.

[0070] Simulate the current crown shape parameters CMD_N(i, d, h′, w′) of Chinese fir without adding the influence of light.

[0071] Step 2: Crown morphology simulation based on the Chinese fir crown-light coupling model

[0072] The current fir crown parameters without light effects are coupled with the fir canopy light distribution data LDD (i, d, h, l) to solve the fir crown-light coupling model of the current stand:

[0073] CMD=Intercept+b*CMD_N+c*LDD

[0074] Where: CMD is the current crown shape data of Chinese fir, Intercept is a constant, b and c are coefficients, CMD_N is the current crown shape simulation data of Chinese fir without considering the influence of light, and LDD is the light distribution data of Chinese fir canopy.

[0075] The model is used to calculate the crown shape data driven by light and simulate the current crown of Chinese fir.

[0076] Calculate the Euclidean distance between the current Chinese fir crown data CMD(i, d, h', w) and the crown data CMD_CCLM(i, d, h', w') simulated based on the Chinese fir crown-light model:

[0077]

[0078] Where D is the calculated Euclidean distance, x i and y i are the crown widths at the corresponding positions of each set of crown shape description data, and n represents the number of crown shape description data.

[0079] Determine the simulation effect. The smaller the Euclidean distance, the better the fitting effect.

[0080] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for visual simulation of tree crown growth based on an illumination model, characterized in that: Based on the three-dimensional forest model constructed using periodic B-spline curves, the relationship between the crown shape changes of trees in previous and subsequent years and the canopy light distribution of the current year is studied in combination with the forest growth model. A forest crown-light coupling model is constructed to achieve a visual simulation of the tree crown morphology based on the light model. The following steps are involved: Step 1: Construction of a Chinese fir canopy-light coupling model, including: Step 1.1: Obtain the crown shape data of Chinese fir trees in the base period from the sample site survey, that is, the data of each crown shape measurement point, which is represented by a set of (i, d, h, w), which represents the crown width w at the corresponding Chinese fir tree number i, corresponding direction d, and corresponding height h. Step 1.2: Use a set of (h, w) as the base points of the periodic B-spline curve to construct the crown curve of the Chinese fir, thereby obtaining the crown curves of each Chinese fir in the four directions of southeast, northwest, and northeast. Then, construct a three-dimensional model of the Chinese fir from the crown curves of the Chinese fir in the four directions. Combine the terrain data and the spatial position data of the Chinese fir to construct a three-dimensional scene of the Chinese fir stand. In the three-dimensional scene of the Chinese fir stand, combine the ray tracing algorithm, use the annual average photosynthetically active radiation as the light parameter, calculate the light intensity at the Chinese fir crown measurement point, and obtain the Chinese fir canopy light distribution data LDD, which is expressed as a set of (i, d, h, l) data, representing the light intensity l at the corresponding Chinese fir number, corresponding direction d, and corresponding height h, corresponding to the base period Chinese fir crown data (i, d, h, w). Step 1.3: The base period Chinese fir attribute data were also obtained from the plot survey and expressed as (i, D, H), where i represents the Chinese fir tree number, D represents the DBH, and H represents the tree height. By combining the DBH growth model and the height-DBH curve model, the current period Chinese fir attribute simulation data (i, D, H) without adding the influence of light were obtained. , ) and the current simulated crown shape data of Chinese fir without adding the influence of light CMD_N (i, d, , ), the crown shape data of the base period Chinese fir and the current period Chinese fir crown shape simulation data without adding the influence of light, the crown shape has not changed, only the proportion has changed. Step 1.4: Construct a crown curve of Chinese fir using field survey data, and obtain the current crown data CMD (i, d, , w), studied the relationship between light distribution data, current crown shape data and current fir crown shape simulation data without light influence, and finally used statistical methods to construct the fir crown-light coupling model formula (1), where CMD represents current crown shape data, CMD_N represents current fir crown shape simulation data without light influence, LDD represents light distribution data, a is the intercept, b and c are coefficients, （1）。 2. The method for visual simulation of tree crown growth based on an illumination model according to claim 1, characterized in that: Step 2: Crown morphology simulation based on the Chinese fir crown-light coupling model, including: Step 2.1: Combine the base period Chinese fir attribute data and base period Chinese fir crown data with the DBH growth model and the tree height-curve model to obtain the current period Chinese fir crown simulation data CMD_N without considering the influence of light. Step 2.2: Substitute the canopy light distribution data LDD of Chinese fir and the current simulated crown shape data CMD_N without considering the influence of light into the constructed crown-light coupling model to obtain the crown shape data that considers the influence of light factors on the crown shape of Chinese fir, that is, obtain the crown shape simulation data CMD_CCLM based on the Chinese fir crown-light model. Step 2.3: The current crown shape data (CMD) of Chinese fir is obtained from the plot survey. Both CMD and CMD_CCLM are crown shape data, and are represented by a set (i, d, h, w). The similarity between the two sets of crown shapes is measured by the Euclidean distance of the crown shape data. Step 2.4: Calculate the Euclidean distance D_CCLM between CMD and CMD_CCLM. The smaller the Euclidean distance, the better the fitting effect.

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