Method for calculating light transmittance of plant leaves through point cloud approximation

Abstract

The invention discloses a method for calculating the light transmittance of a plant leaf through point cloud approximation, and relates to the technical field of three-dimensional measurement data processing, and the method comprises the following steps: 1, calculating a light receiving point, and taking the midmost and lowermost positions pr of a plant as the light receiving point; step 2, clustering the plant point clouds; 3, calculating a solid angle of the bounding box, and selecting a shaft to align the bounding box; and 4, calculating the light transmittance. According to the method for calculating the light transmittance of the plant leaf through the point cloud approximation, the algorithm is simple, the calculation speed is high, the estimated light transmittance value can reflect the capacity of light penetrating through the overground part of the plant, the estimated light transmittance value is in negative correlation with the projection area, the volume, the leaf length, the leaf width and the leaf area of the plant leaf, and the plant growth law is met.

Description

Technical Field

[0001] The present invention relates to the technical field of three-dimensional measurement data processing, and in particular to a method for approximately calculating the light transmittance of plant leaves through point clouds. Background Art

[0002] Light transmittance is the ratio of the remaining light intensity after passing through a plant's canopy to the light intensity above the canopy. It is a key parameter describing the ability of light to penetrate the aboveground parts of a plant (such as stems, leaves, and flowers) to reach the lower layers or the ground. It can be used to reflect the structure of the plant canopy and leaf density. Traditional methods often use light intensity meters (such as PAR sensors) to measure light simultaneously above and below the canopy. In recent years, with the widespread availability of 3D sensors, the methods for obtaining 3D point clouds of plants have become increasingly diverse and cost-effective. Non-contact measurement of plant 3D structure using point clouds has become a common practice in agricultural and forestry research. However, a simple and rapid method for estimating the light transmittance of plant aboveground parts using point clouds is currently lacking. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for calculating the light transmittance of plant leaves by approximating point clouds, which can be used for dynamic monitoring of plant growth, plant type evaluation and three-dimensional phenotyping detection.

[0004] To achieve the above object, the present invention provides a method for approximately calculating the light transmittance of plant leaves using point clouds, comprising the following steps:

[0005] Step 1: Calculate the light receiving point, taking the middle and bottom positions of the plant as the r As a light receiving point;

[0006] Step 2: Cluster the plant point cloud;

[0007] Step 3: Calculate the solid angle of the bounding box and select the axis-aligned bounding box.

[0008] Step 4: Calculate the transmittance.

[0009] Preferably, in step 1, P [n] ={p1…p n} represents the peanut plant point cloud, P [n] The i-th point p i The three-dimensional coordinates are (x i ,y i ,z i ), then p r The coordinates (x r ,y r ,z r )for:

[0010]

[0011] Preferably, in step 2, the k-means clustering method is used to cluster the peanut plant point cloud to form n2 peanut point cloud instances.

[0012] Preferably, in step 3, the solid angle α opened by the bounding box on the plant hemisphere is:

[0013] α=(φ max (i)-φ min (i))·(cosθ min (i) -cosθ max (i));

[0014] Where: φ is the distance between the vertex and the light receiving point p r The angle between the vector and the X axis, θ is the angle between the vertex and the light receiving point p r The angle between the vector and the Z axis, i is an instance.

[0015] Preferably, in step 3, the solid angle of the i-th instance is calculated by subtracting the solid angle opened by the overlapping area. The solid angle β opened by the overlapping area is

[0016]

[0017] Where: m o is the number of overlapping areas, and the φ value range of the kth overlapping area is The angle range of θ is

[0018] Preferably, the light transmittance PT of the aboveground part of the plant in step 4 is:

[0019]

[0020] Where: solid angle is s = α - β.

[0021] Therefore, the present invention adopts the above-mentioned method of approximately calculating the transmittance of plant leaves through point clouds. The algorithm is simple and the calculation speed is fast. The estimated transmittance value can reflect the ability of light to pass through the above-ground part of the plant, and is negatively correlated with the projected area, volume, leaf length, leaf width and leaf area of ​​the plant leaves, which is in line with the law of plant growth.

[0022] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a flow chart of a method for approximately calculating the light transmittance of plant leaves through point clouds according to the present invention;

[0024] Figure 2 This is a point cloud image of a peanut plant according to the present invention;

[0025] Figure 3 This is a schematic diagram of calculating the transmittance coefficient of the present invention. DETAILED DESCRIPTION

[0026] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0027] Unless otherwise defined, the technical or scientific terms used in the present invention shall have the usual meanings understood by persons of ordinary skill in the field to which the present invention belongs. The words "first", "second" and similar terms used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. Words such as "include" or "comprise" mean that the elements or objects preceding the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Words such as "connect" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0028] Example

[0029] See also Figure 1-3 The present invention provides a method for approximately calculating the light transmittance of plant leaves by using a point cloud, comprising the following steps:

[0030] Step 1: Calculate the light receiving point p r , select any point inside the plant canopy as the light receiving point to evaluate the light transmittance of that point. In the absence of manual selection, the center and bottom positions of the plant will be automatically selected. r The light transmittance of the aboveground part of the whole plant is calculated as the light receiving point. [n] ={p1…p n} represents the peanut plant point cloud, P [n] The i-th point p i The three-dimensional coordinates are (x i ,y i ,z i ), then p r The coordinates (x r ,y r ,z r )for:

[0031]

[0032] Here, min represents the minimum value.

[0033] Step 2: Cluster the plant point cloud. This paper uses the k-means clustering method to cluster the peanut plant point cloud, forming n2 peanut point cloud instances. n2 is a manually selected parameter. A larger value results in more accurate calculations, but also increases the computational complexity. In this study, n2 was set to 60.

[0034] Step 3: Calculate the bounding box of the instance. To speed up the calculation efficiency, the present invention selects the axis-aligned bounding box as the bounding box of each instance. Extract the minimum X coordinate X of the point cloud in the instance min , maximum X coordinate X max , minimum Y coordinate Y min , maximum Y coordinate Y max , minimum Z coordinate Z min , maximum Z coordinate Z max , then the 8 vertices of the bounding box of this instance are (X min ,Y min ,Z min )、(X min ,Y max ,Z min )、(X max ,Y max ,Z min )、(X max ,Y min ,Z min ),

[0035] (X min ,Y min ,Z max )、(X min ,Y max ,Z max )、(X max ,Y max ,Z max ),

[0036] (X max ,Y min ,Z max ).

[0037] Step 4: Calculate the transmittance.

[0038] Calculate the 8 vertices of the bounding box of the i-th instance and the light receiving point p r The vectors between them are calculated, and the angle φ between each vector and the X axis and the angle θ between each vector and the Z axis are calculated. The maximum and minimum values ​​of the 8 φ are φ respectively. max (i) and φ min (i) The maximum and minimum values ​​of the 8 θ are θ max (i) and θ min (i), then the bounding box is considered to have a range of [φ min (i),φmax (i)], the range at angle θ is [θ min (i),θ max (i)], we approximately calculate the solid angle α of the bounding box on the plant hemisphere as:

[0039] α=(φ max (i)-φ min (i))·(cosθ min (i) -cosθ max (i));

[0040] Since the solid angles opened by the bounding boxes of different instances on the hemisphere may overlap, when calculating the solid angle of the i-th instance, we need to determine whether the φ and θ angle ranges of the first i-1 instances overlap with those of the i-th instance, and subtract the solid angles opened by the overlapping areas to ensure that the overlapping areas are not calculated multiple times. The solid angle β opened by the overlapping areas is:

[0041]

[0042] Where m o is the number of overlapping areas, and the φ value range of the kth overlapping area is The angle range of θ is The solid angle of the i-th instance is s = α - β. The final light transmittance PT of the entire plant above ground is:

[0043]

[0044] Therefore, the present invention adopts the above-mentioned method of approximately calculating the transmittance of plant leaves through point clouds. The algorithm is simple and the calculation speed is fast. The estimated transmittance value can reflect the ability of light to pass through the above-ground part of the plant, and is negatively correlated with the projected area, volume, leaf length, leaf width and leaf area of ​​the plant leaves, which is in line with the law of plant growth.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for approximating the light transmittance of plant leaves by using point clouds, characterized in that: The following steps are involved: Step 1: Calculate the light receiving point, taking the middle and bottom positions of the plant as the r As a light receiving point; Step 2: Cluster the plant point cloud; Step 3: Calculate the solid angle of the bounding box and select the axis-aligned bounding box. Step 4: Calculate the transmittance.

2. The method for approximately calculating the light transmittance of plant leaves by using a point cloud according to claim 1, characterized in that: In step 1, use P [n] ={p1…p n } represents the peanut plant point cloud, P [n] The i-th point p i The three-dimensional coordinates are (x i ,y i ,z i ), then p r The coordinates (x r ,y r ,z r )for:

3. The method for approximately calculating the light transmittance of plant leaves by using point clouds according to claim 2, characterized in that: In step 2, the k-means clustering method is used to cluster the peanut plant point cloud to form n2 peanut point cloud instances.

4. The method for approximately calculating the light transmittance of plant leaves using point clouds according to claim 3, wherein: The solid angle α of the bounding box in step 3 on the plant hemisphere is: a=(φ max (i)-φ min (i))·(cosθ min (i)-cosθ max (i)); Where: φ is the distance between the vertex and the light receiving point p r The angle between the vector and the X axis, θ is the angle between the vertex and the light receiving point p r The angle between the vector and the Z axis, i is an instance.

5. The method for approximately calculating the light transmittance of plant leaves using point clouds according to claim 4, characterized in that: In step 3, the solid angle of the i-th instance needs to be calculated by subtracting the solid angle opened by the overlapping area. The solid angle β opened by the overlapping area is Where: m o is the number of overlapping areas, and the φ value range of the kth overlapping area is The angle range of θ is 6. The method for approximately calculating the light transmittance of plant leaves using point clouds according to claim 5, characterized in that: The light transmittance PT of the aboveground part of the plant in step 4 is: Where: solid angle is s = α - β.

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