Tree crown estimation system

Abstract

To provide a tree crown estimation system designed to solve the conventional problem and capable of estimating a shape of a tree crown more accurately than conventional techniques even in the case of a tree located on a slope.SOLUTION: This tree crown estimation system is for estimating a shape of a tree crown on the basis of a numerical surface layer model indicating the height of a ground surface layer and a numerical elevation model indicating the height of a ground surface, and comprises: tree top selection means; reference height setting means; and tree crown height calculation means. The reference height setting means is for setting a "reference height" which is a height of the numerical elevator model at the tree top. The tree crown height calculation means is for calculating a "tree crown height" which is a level difference between the numerical surface layer model in a target tree and the reference height.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a technique related to the shape of a tree crown, and more specifically, to a tree crown estimation system that estimates the shape of a tree crown after setting a reference height for a target tree.

Background Art

[0002] Wood such as columns and boards is an indispensable material for wooden buildings including detached houses. In the past, a large amount of wood could be imported from overseas, but since the 1980s, movements to stop deforestation have become active in various countries, and recently domestic production has been attracting attention. Currently, the self-sufficiency rate of wood is said to be 35% (27 million m 3 ), but it is expected that the maturation of domestic wood will further progress in the future, and forestry is expected to be a growing industry in our country.

[0003] The market price of materials (raw materials) cut from trees varies depending on the degree of bending of the axis (hereinafter referred to as "axis shape") such as the rise (degree of bending of the curve) and curvature, and the trunk diameter. For example, the closer the axis shape is to a straight line and the trunk diameter with demand, the higher the price. Although it is not realistic to predict the axis shape and trunk diameter of the raw material in advance, it is generally practiced to grasp the trunk diameter in the state of standing trees. Specifically, a method of estimating the breast height diameter of the tree using the area and volume of the tree crown as parameters can be mentioned.

[0004] When grasping the tree crowns of trees in a forest, methods such as airborne laser scanning and aerial photogrammetry are the mainstream. Among these, airborne laser scanning is a method of flying an aircraft over the target area to be measured and measuring by receiving the reflected wave of the laser pulse irradiated on the ground, etc. within this target area. Usually, since the aircraft is equipped with a positioning meter such as GNSS (Global Navigation Satellite System) and an inertial measurement device such as IMU (Inertial Measurement Unit), the irradiation position (x, y, z) and irradiation attitude (ω, φ, κ) at the time of laser pulse irradiation can be recorded by these GNSS and IMU.

[0005] When measuring a target area such as a forest by airborne laser scanning, a large number of measurement point data with three-dimensional coordinates (hereinafter referred to as "three-dimensional point cloud") are obtained. Since the three-dimensional point cloud is composed of random data (data with an irregular arrangement in a plane), it is common to generate a terrain model in order to facilitate its use. This terrain model is composed of small areas (so-called meshes) obtained by dividing the planar range of the measurement target, and each mesh has a representative point with an elevation assigned thereto. Among the terrain models, the one representing the surface of the covering such as a forest or a building is the "Digital Surface Model (DSM)", and the one representing the ground with the covering removed by filtering processing is the "Digital Elevation Model (DEM)".

[0006] As described above, in order to estimate the breast height diameter of a tree, it is necessary to grasp the area and volume of the tree crown. For this purpose, it is necessary to find the apex of the tree crown and grasp the range of the tree crown based on this apex. Conventionally, when finding the apex of the tree crown, the "Digital Canopy Height Model (DCHM)", which is the difference between the Digital Surface Model (DSM) and the Digital Elevation Model (DEM), has been used. For example, in Patent Document 1, a technique is proposed for extracting the maximum point of the Digital Canopy Height Model (DCHM) as the apex of the tree and estimating the tree interval according to the tree characteristics at that apex.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] By the way, forests naturally include sloped areas, and the tree canopies on the sloped areas have significantly different height differences from the ground. Specifically, even for the same tree, the distance between the tree canopy and the ground is shorter at a position with a higher ground elevation, but tends to be longer at a position with a lower ground elevation. Therefore, for example, if the apex of the tree canopy is simply determined from the Digital Canopy Height Model (DCHM) on a steep slope, it may be different from the actual position.

[0009] FIG. 7(a) is a graph showing a Digital Surface Model (DSM) obtained by measuring three patterns of tree canopies, that is, a tree canopy pattern with a canopy length of 2.5 m and an appearance generally showing a triangle (hereinafter referred to as "tree canopy pattern 1"), a tree canopy pattern with a canopy length of 5.0 m and an appearance generally showing a triangle (hereinafter referred to as "tree canopy pattern 2"), and a tree canopy pattern with an appearance generally showing a trapezoid (hereinafter referred to as "tree canopy pattern 3"). On the other hand, FIG. 7(b) is a graph showing a Digital Elevation Model (DEM) obtained by measuring five patterns of ground with different inclination angles, that is, the ground shape with an inclination angle of 0 degrees (i.e., horizontal), the ground shape with an inclination angle of 30 degrees, the ground shape with an inclination angle of 60 degrees, the ground shape along the road, and the V-shaped ground shape. And FIG. 8 is a graph showing a Digital Canopy Height Model (DCHM) obtained by the difference between each tree canopy pattern and the five patterns of ground. (a) shows the canopy height model in tree canopy pattern 1, (b) shows the canopy height model in tree canopy pattern 2, and (c) shows the canopy height model in tree canopy pattern 3. The horizontal axes of FIGS. 7 and 8 represent the horizontal distance from a predetermined reference position.

[0010] If the ground surface is horizontal, it is considered that the highest point among the canopy height models indicates the apex of the canopy. Therefore, looking at the canopy height model based on the horizontal ground in Fig. 8, it can be seen that the apexes of the three patterns of canopies are respectively at positions with a horizontal distance of about 3.0 m. However, looking at the canopy height model based on the sloping ground, the highest point appears at a position different from 3.0 m in horizontal distance. That is, when determining the apex of the canopy from the canopy height model on the sloping ground, the result shows the wrong position.

[0011] The problem of the present invention is to solve the conventional problems, that is, to provide a canopy estimation system that can estimate the shape of the canopy with higher accuracy than the prior art even for trees on sloping ground.

Means for Solving the Problems

[0012] The present invention focuses on the fact that for trees on sloping ground, a reference horizontal plane is set and then the shape of the canopy is estimated, and it is an invention made based on an idea that has never existed before.

[0013] The canopy estimation system of the present invention is a system that estimates the shape of the canopy based on a "Digital Surface Model (DSM)" indicating the height of the ground surface layer and a "Digital Elevation Model (DEM)" indicating the height of the ground surface. It is equipped with a tree apex selection means, a reference height setting means, and a canopy height calculation means. Among these, the tree apex selection means is a means for selecting, as the "tree apex", the planar position indicating the maximum height from the digital surface model related to the target tree being focused on. The reference height setting means is a means for setting the "reference height", which is the height of the digital elevation model at the tree apex, and the canopy height calculation means is a means for calculating the "canopy height", which is the height difference between the digital surface model related to the target tree and the reference height. Then, based on the canopy heights obtained at a plurality of planar positions, the shape of the canopy of the target tree can be estimated.

[0014] The tree crown estimation system of the present invention can also be further provided with a tree crown volume calculation means. This tree crown volume calculation means is a means for calculating the tree crown volume of a target tree based on the tree crown heights obtained at a plurality of planar positions.

[0015] The tree crown estimation system of the present invention can also be further provided with a slope calculation means. This slope calculation means is a means for calculating a ground slope indicating the slope of the ground surface based on a digital elevation model of the range of the target tree. In this case, when the ground slope exceeds a predetermined threshold value, the tree crown height calculation means calculates the tree crown height based on the digital surface model and the reference height.

Effects of the Invention

[0016] The tree crown estimation system of the present invention has the following effects. (1) Even for trees on sloping ground, the shape of the tree crown can be estimated with higher accuracy than in the prior art. (2) As a result of accurately estimating the shape of the tree crown, the breast height diameter of the tree can also be accurately estimated.

Brief Description of the Drawings

[0017]

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Embodiment for Carrying Out the Invention

[0018] An example of an embodiment of the tree crown estimation system of the present invention will be described with reference to the drawings. The present invention estimates the shape of a tree crown using a digital surface model (hereinafter simply referred to as "DSM") representing the surface of the tree crown of a tree and a digital elevation model (hereinafter simply referred to as "DEM") representing the ground. Conventionally, a tree crown height model (hereinafter simply referred to as "DCHM"), which is simply the difference between DSM and DEM, has been used. However, the present invention uses a reference horizontal plane (hereinafter referred to as the "reference height plane") as one of its technical features.

[0019] Figure 1 is a block diagram showing the main configuration of the tree crown estimation system 100 of the present invention. As shown in this figure, the tree crown estimation system 100 of the present invention includes a tree top point selection means 101, a reference height setting means 102, and a tree crown height calculation means 103, and can further include a tree crown volume calculation means 104, an inclination degree calculation means 105, a tree crown area setting means 106, a tree crown surface area calculation means 107, a DSM data storage means 108, a DEM data storage means 109, a tree height calculation means 110, and the like.

[0020] The tree top point selection means 101, the reference height setting means 102, the tree crown height calculation means 103, the tree crown volume calculation means 104, the inclination degree calculation means 105, the tree crown area setting means 106, the tree crown surface area calculation means 107, and the tree height calculation means 110 can be manufactured as dedicated ones, or a general-purpose computer device can also be used. That is, by causing the computer device to execute arithmetic processing according to a predetermined program, the processing of various means is performed. This computer device includes a processor such as a CPU (Central Processing Unit) or a GPU (Graphics Processing Unit), and a memory such as a ROM or a RAM. Some also include input means such as a mouse and a keyboard and a display, and can be configured by, for example, a personal computer (PC) or a server.

[0021] The DSM data storage means 108 and the DEM data storage means 109 can use the storage device of a general-purpose computer (for example, a personal computer), or can be constructed in a database server. When constructing in a database server, it can be placed in a local area network (LAN: Local Area Network), or can be a cloud server stored via the Internet.

[0022] Hereinafter, each main element constituting the tree crown estimation system 100 of the present invention will be described in detail.

[0023] (DSM Data Storage Means and DEM Data Storage Means) The DSM data storage means 108 is a means for storing DSM data, and the DEM data storage means 109 is a means for storing DEM data. As described above, DSM and DEM are each composed of a plurality of meshes. Therefore, for the sake of distinction, here, for the sake of convenience, the mesh constituting DSM is particularly referred to as "DSM mesh", and the mesh constituting DEM is particularly referred to as "DEM mesh".

[0024] (Tree Top Point Selection Means) The tree top point selection means 101 is a means for selecting a "tree top point" for each tree based on the DSM. Here, the tree top point is the point indicating the top of the tree crown as shown in FIG. 2, and is the point at the highest position in the tree crown. When the tree top point selection means 101 selects the tree top point for each tree, a predetermined range (hereinafter referred to as the "scanning window") is set in advance. This scanning window can be set in any shape, and for example, in FIG. 3, it is set as a rectangle as the scanning window. Also, it is desirable to set the planar dimensions of the scanning window according to the distance between adjacent trees, and for example, it may be set based on the results of partial observation on site.

[0025] As shown in FIG. 3, the tree top point selection means 101 selects the tree top point while horizontally moving the scanning window. It may select the same tree top point without change even when the scanning window moves, or may select a new tree top point at the moved timing. Then, when a tree top point is selected, it is determined that there is a tree for each tree top point.

[0026] (Crown area setting means and crown surface area calculating means) The crown area setting means 106 is a means for setting a "crown area" for each tree. Here, the crown area is a planar area where the tree crown spreads as shown in FIG. 2. Hereinafter, the procedure for the crown area setting means 106 to set the crown area for each tree will be described. First, a "search range" is set with the tree top point as a reference. This search range is a predetermined range set in advance, and can be set in any shape such as a circle centered on the tree top point, for example. Also, the planar dimensions of the search range (for example, the radius) are desirably set according to the distance between adjacent trees, similar to the scanning window, and for example, it may be set based on the results of partial observation on site.

[0027] When a search range is set for each tree, that is, for each tree top point, a "tree crown boundary" is set within that search range. This tree crown boundary is set at a position assumed to be the periphery of the crown of the target tree (hereinafter referred to as the "target tree"), such as being set based on the DSM mesh clearly showing the ground as shown in Fig. 2, or being set based on the DSM mesh of adjacent tree crowns. Then, based on the tree crown boundary included in the search range, a tree crown area is set so as to further limit the search range. Therefore, when no tree crown boundary is detected in the search range related to the target tree, the search range is set as the tree crown area as it is. When the tree crown area is set by the tree crown area setting means 106, the tree crown surface area calculating means 107 calculates the area occupied by the tree crown area (hereinafter referred to as the "tree crown surface area").

[0028] (Reference height setting means) The reference height setting means 102 is a means for setting a "reference height" for each tree based on the DEM. Here, the reference height is the height of the ground directly below the tree top point, as shown in Fig. 4, and more specifically, it is the elevation given to the DEM mesh related to the planar position of the tree top point. In other words, the reference height is the elevation of the point where the vertical line passing through the tree top point intersects the DEM, that is, the elevation at the ground position supporting the target tree. Also, when the reference height setting means 102 sets a reference height for each tree, that is, for each tree top point, the horizontal plane with that reference height is set as the "reference height plane".

[0029] (Tree crown height calculating means and tree height calculating means) The tree crown height calculating means 103 is a means for calculating the "tree crown height" for each tree based on the DSM and the reference height, and the tree height calculating means 110 is a means for calculating the "tree height". Here, the reference height is, as shown in Fig. 4, the difference (height difference) between the DSM representing the crown of the target tree and the reference height (that is, the reference height plane) set for that target tree, while one tree height is the height difference from the ground surface to the crown surface. Note that the tree crown height calculating means 103 calculates the tree crown height using all the DSM meshes included in the crown area of the target tree, that is, the tree crown height is obtained at a plurality of planar positions within the crown area.

[0030] (Canopy volume calculation means) The canopy volume calculation means 104 is a means for calculating the volume of the canopy of the target tree (hereinafter referred to as "canopy volume"). Specifically, the canopy volume is calculated based on the canopy heights obtained at a plurality of planar positions in the canopy area of the target tree. In other words, the canopy volume is calculated by integrating the canopy height over the canopy area.

[0031] (Gradient calculation means) The gradient calculation means 105 is a means for calculating the "ground gradient", which is the inclination of the ground of the target tree. This ground gradient can be calculated, for example, as the inclination of the ground with respect to the horizontal plane as shown in FIG. 5. As described above, when simply determining the apex of the canopy from the DCHM on a steep slope, the result shows an incorrect position. On the other hand, it is also considered that if the ground surface is a gentle slope close to horizontal, a generally correct position can be obtained even if the apex of the canopy is determined from the DCHM. Therefore, the canopy estimation system 100 of the present invention can be configured to set a reference height (reference height plane) according to the ground gradient obtained by the gradient calculation means 105 and calculate the canopy height. That is, when the ground gradient exceeds a predetermined threshold (hereinafter referred to as "gradient threshold"), the canopy height is calculated after setting the reference height, and when the ground gradient is equal to or less than the gradient threshold, the DCHM is used. When comparing the ground gradient and the gradient threshold, it can be determined for each target tree, or it can be determined for a predetermined range (a relatively wide range).

[0032] (Flow of processing) Hereinafter, with reference to FIG. 6, the main processing of the canopy estimation system 100 of the present invention will be described in detail. FIG. 6 is a flowchart showing the flow of the main processing of the canopy estimation system 100 of the present invention. The processing to be performed is shown in the central column, the input to the processing is shown in the left column, and the output from the processing is shown in the right column.

[0033] When estimating the shape of the tree crown by the tree crown estimation system 100 of the present invention, as shown in FIG. 6, first, the tree top point selection means 101 reads the DSM data from the DSM data storage means 108, and then selects the tree top points using a preset scanning window, and sets the trees corresponding to the tree top points (Step 201 in FIG. 6).

[0034] When the tree top points are selected, the tree crown area setting means 106 sets a search range (for example, a circle centered on the tree top point) for each target tree, and further sets the tree crown area based on the tree crown boundary detected within the search range (Step 202 in FIG. 6). Then, the tree crown surface area calculation means 107 calculates the tree crown surface area based on the tree crown area (Step 203 in FIG. 6).

[0035] When the tree crown area is set, the reference height setting means 102 reads the DEM data from the DEM data storage means 109, and then sets the reference height and the reference height plane corresponding to the tree top point (Step 204 in FIG. 6). Next, the tree crown height calculation means 103 calculates the tree crown height based on the reference height plane and the DSM data (Step 205 in FIG. 6), and the tree crown volume calculation means 104 calculates the tree crown volume based on the tree crown height and the tree crown area (Step 206 in FIG. 6).

Industrial Applicability

[0036] The tree crown estimation system of the present invention can be used for various areas where trees grow in groups, such as natural forests and plantations. Considering that the present invention can improve the estimation accuracy of the breast height diameter of trees, and thus can be expected to activate the forestry industry in our country, it can be said that the invention is not only industrially applicable but also can be expected to make a great social contribution.

Explanation of Reference Numerals

[0037] 100 Tree crown estimation system of the present invention 101 Tree top point selection means (of the tree crown estimation system) 102 Reference height setting means (of the tree crown estimation system) 103 Tree crown height calculation means (of the tree crown estimation system) 104 Canopy volume calculation means (of the canopy estimation system) 105 Slope calculation means (of the canopy estimation system) 106 Canopy area setting means (of the canopy estimation system) 107 Canopy surface area calculation means (of the canopy estimation system) 108 DSM data storage means (of the canopy estimation system) 109 DEM data storage means (of the canopy estimation system) 110 Tree height calculation means (of the canopy estimation system)

Claims

1. A system for estimating the shape of a tree crown based on a numerical surface model indicating the height of the ground surface layer and a numerical elevation model indicating the height of the ground surface, comprising: Tree top point selection means for selecting, as a tree top point, a planar position indicating the maximum height from the numerical surface model related to the target tree of interest; Reference height setting means for setting a reference height which is the height of the numerical elevation model at the tree top point; Crown height calculation means for calculating a crown height which is the height difference between the numerical surface model related to the target tree and the reference height, and being able to estimate the shape of the tree crown of the target tree based on the crown heights obtained at a plurality of planar positions. A tree crown estimation system characterized by the above.

2. The tree crown estimation system according to claim 1, further comprising crown volume calculation means for calculating the crown volume of the target tree based on the crown heights obtained at a plurality of planar positions.

3. The tree crown estimation system according to claim 1, further comprising inclination degree calculation means for calculating a ground inclination degree indicating the inclination of the ground surface based on the numerical elevation model within the range of the target tree, wherein the crown height calculation means calculates the crown height based on the numerical surface model and the reference height when the ground inclination degree exceeds a predetermined threshold value. 【Claim X】 The tree crown estimation system according to claim 1, characterized by the above.

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