CN102914501B - Method for calculating extinction coefficients of three-dimensional forest canopy by using laser-point cloud - Google Patents
Method for calculating extinction coefficients of three-dimensional forest canopy by using laser-point cloud Download PDFInfo
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Abstract
The invention provides a method for calculating the extinction coefficients of a three-dimensional forest canopy under any given incident ray by using a geometric algorithm, belonging to the research field of a method of acquiring the structural parameters of the forest canopy. The method for calculating the extinction coefficients of the three-dimensional forest canopy by using the geometric algorithm comprises the following steps: acquiring and preprocessing the three-dimensional laser-point cloud data of a plant canopy; carrying out three-dimensional gridding on the point cloud data; carrying out point cloud slice arithmetic based on a voxel data structure; carrying out linear sampling analysis on the point cloud slices; calculating an average projection coefficient of a kth layer of slices; and calculating the extinction coefficient of any given incident ray in each layer of slices and the extinction coefficient of whole canopy. Compared with the traditional observing way, the invention has the characteristics of being small in working amount, and free from the contact observation and the damage of the canopy structure and radiation, and has objectiveness, high efficiency and precision; a method of extracting the three-dimensional structures and biological and physical diversity information from the laser radar data is developed to characterize the horizontal and vertical distribution change rules of the leaves.
Description
One, technical field
The present invention relates to a kind of method that cloud data utilizing Three Dimensional Ground laser scanner to obtain calculates Forest Canopy extinction coefficient, specifically, what refer to a kind of improvement utilizes computational geometry algorithm to calculate the method (flow process as shown in Figure 1) of the extinction coefficient under any given incident ray of three-dimensional Forest Canopy.
Two, background technology
Forest Canopy structure occupies an important position in the interaction of soil-canopy-air, and closely related with the Exchange of material and energy in biogeochemical cycle.Extinction coefficient is defined as unit leaf area perpendicular to the averaging projection's area in the plane of radiation direction, is the important factor of quantitative understanding Forest Canopy structure and radiation transmission.He is the directional distribution function (comprising inclination angle and azimuthal distribution function) based on Leaf inclination, and the incident ray for any given angle calculates.
The Leaf angle inclination distribution density function obtaining Vegetation canopy indirectly, is exactly a challenging job all the time, and traditional method mainly utilizes the method directly observed by blade to obtain the Leaf angle inclination distribution density function of given isolated tree.Such as: a kind of instrument (accompanying drawing 2 is left) measuring blade angle and space distribution comparatively simply and easily of the equipment makings such as people's utilization hornwork and compass such as Norman; The people such as Lang utilize the dirigibility of mechanical arm and cleverly geometry transitive relation made a kind of instrument (accompanying drawing 2 is right) being used for measuring blade space and angular distribution that can move freely and stretch.
But because its workload is large, subjectivity is strong, and the limited height system to measured target trees, so can not be widely used in practical study.Even more important a bit direct observation often affects the structure of even vegetation destruction canopy, and then destroys the inner and following radiation profiles situation of canopy.And with regard to forest, be difficult in reality utilize direct observation instrument to carry out by Blade measuring.Therefore, need a kind of quick, accurate, round-about way newly to obtain angle and the space distribution situation of canopy leaves.In recent years, also someone start trial indirectly obtain blade tilt distribution.Such as, within 2007, Shilbayama and Watanabe is published in " Estimating the mean leaf inclination angle of wheat canopies using reflected polarized light " literary composition of periodical " Plant Production Science " the 10th volume, proposes to utilize reflecting polarised light to the evaluation method of the Leaf inclination that is averaged..
At present, a kind of comparatively popular method is also had to be the blade actual distribution utilizing mathematics geometric model to carry out approaching to reality trees approx, wherein widely accepted what model of spheroid being Campbell and proposing in the eighties in 20th century.Its core concept is that the different distributions at each tangent plane inclination angle, spheroid surface carrys out the angular distribution of the actual blade of approximate expression, and regulates the change of different angle distribution density function by the long and short axle of adjustment spheroid.The method can use following equation expression:
Wherein
When χ=1, this distribution will become sphere distribution, and now Λ=2, a, b are half short, semi-major axis of spheroid respectively.But the actual distribution of approaching blade that this method is just approximate in theory, is not enough to describe protean truth.
The appearance of ground laser radar scanner makes us directly can obtain the Forest Canopy structural information of high precision (grade) from three-dimensional perspective, and then calculates the extinction coefficient of canopy.Domestic about the applied research of laser radar in forest at present, the research particularly for three-dimensional canopy structure is also in starting and exploratory stage.Existing research major part concentrates on parameter (comprising the diameter of a cross-section of a tree trunk 1.3 meters above the ground, the height of tree and biomass etc.) the extraction aspect utilizing ground laser radar to carry out basic every wooden dipping of higher or forest sample ground level.Such as: the people such as Ma Liqun in 2011 describe laser radar and extracting the application in Forest Vertical structural parameters in " application of laser radar in the estimation of Forest Vertical structural parameters " literary composition of " World Forestry research " the 1st volume; In the forest application aspect of laser radar, generating high-precision digital terrain model is a wherein crucial step, the people such as Zhou Shufang 2007 " remote sensing technology and application " the 22nd volume " DEM based on airborne laser radar data obtains and applies " literary composition in inquired into the method and the exact evaluation that utilize airborne laser radar system to generate digital terrain model.In addition, the people such as Pang Yong has carried out a large amount of more deep research to the height of tree estimation having utilized laser radar system to extract forest Dan Mu and sample prescription level between 2006-2009.But the research theory and technology of the domestic three dimensional point cloud extraction canopy extinction coefficient to utilizing laser radar to obtain is deep not enough at present, needs to strengthen further.
Three, summary of the invention
The object of the invention is:
A set of three dimensional point cloud directly utilizing ground laser radar system to generate is provided, in conjunction with the method for computational geometry, calculates the individual plant trees of any given incident light or the algorithm of forest sample prescription extinction coefficient from three-dimensional perspective.And the contactless method quick and precisely observing Forest Canopy structural characteristic parameter is provided.
Principle of the present invention is as follows:
Utilize newer remote sensing technology means (Three Dimensional Ground Laser Radar Scanning system), in conjunction with the technological means of computational geometry, individual plant trees the direct acquisition of the angle from three-dimensional assigned direction incident light and the extinction coefficient of forest sample size blade, and then calculate the extinction coefficient of Vegetation canopy.First set up the position that three-dimensional mathematical model accurately locates individual blade, adopt computational geometry method on this basis, gridding is carried out to three dimensional point cloud, utilizes the some cloud of point cloud slicing algorithm to differing heights to classify.Then carry out line sampling analysis, obtain the relevant information that blade intercepts and captures light, and then calculate the projection coefficient of each slicing layer, i.e. extinction coefficient, thus the extinction coefficient obtaining whole canopy.Complete the calculating of averaging projection's coefficient of extinction coefficient under given incident ray and canopy entirety.
Technical scheme of the present invention mainly comprises the following steps:
(1) first utilize ground laser radar scanning system, obtain the three dimensional point cloud of Vegetation canopy.Wherein contain the energy information that the scanning space geometry of impact point and laser beam are rebounded, three-dimensional coordinate directly provides the locus coordinate information of any point, and this is also the basis of the mathematical model in traditional optical theory.First the cloud data obtained carries out image mosaic, and manual removably millet cake cloud.
(2) three dimensional network is formatted.First define the cartesian coordinate system of X, Y, a Z tri-coordinate axis in a territory, cloud sector, all cloud datas are comprised wherein.And cloud data is divided into limited zonule, set up the data structure based on volume elements (voxel), this process is called three dimensional network and formats.Each volume elements by growing (l) wide (w), high (h) three parameters determine its size, all cloud datas are divided into m × n × p volume elements, wherein, m=(X
max-X
min)/w, n=(Y
max-Y
min)/l, P=(Z
max-Z
min)/h.If l=w=h, then volume elements is a cube.With the three-dimensional center of these cloud datas point, i.e. [(X
max-X
min)/2, (Y
max-Y
min)/2, (Z
max-Z
min)/2] be new initial point, set up cartesian coordinate system.Coordinate axis Z is the direction of growth of trunk, and perpendicular to surface level, X, Y-axis are positioned in the plane vertical with Z axis, and Z axis is longitudinal axle, and X, Y-axis are horizontal axle.As shown in accompanying drawing 3 (a, b, c).
(3) point cloud slicing algorithm.After the three dimensional network process of formatting terminates, cloud data is divided into numerous data Layers in direction in length and breadth, namely cuts into slices, and cloud data can be considered the superposition of direction section in length and breadth.Dropping cut slice as Suo Shi accompanying drawing 3 (d).All volume elements be set to (i, j, k) (i=1,2 ..., m; J=1,2 ... n; K=1,2 ..., p).Work as k=1, i and j is the arbitrary value in given area, then can be expressed as ground floor or first cross section all volume elements.
In order to the relative position relation of approximate simulation incident ray and Forest Canopy, develop the slicing mode of another point of rotation cloud.First, by the relative position that cloud data rotation will be simulated to us, then three dimensional network is carried out to it and format.Such dropping cut slice is parallel with the plane at XY axle place, and vertical section is parallel with the plane at Z axis place.We suppose that direct sunlight is injected from zenith direction, parallel with Z-direction.When incident light direction changes, realize by rotating cloud data.
Specifically, the central point of three dimensional point cloud is the initial point of cartesian coordinate system, and cloud data then rotates around X, Y, Z axis according to the needs of a cloud with section relative position.Such as, cloud data is rotated 30 ° around Y-axis, be equivalent to a cloud and cut into slices or sun incident light is cut into slices with the pitch angle of 30 °.Therefore, some cloud can (level 0 °-360 °, vertical 0 °-90 °) be cut into slices at an arbitrary position, is called directivity section.Any cloud data all generates thin plate to extract three-dimensional canopy information by directivity section.
(4) line sampling analysis.Blade space distribution is in a slice analyzed by the line method of sampling.The section of each position of cloud data is made up of many line-transects, and these line-transects are perpendicular or parallel in sun incident light r (θ, β).When studying the distribution along r direction blade, be consider the line-transect parallel with r.If the three-dimensional parameter of each volume elements to be set to 1.5 times of laser radar sampled distance, we can ensure that each volume elements at most only comprises a sampling point.So, in every bar line-transect, volume elements (N) number of non-NULL represents the line-transect number of times crossing with blade, and N obeys stochastic distribution.If be greater than 1.5 times of sampled distance, when comprising multiple sampling point in a volume elements, we to need spot projections all on line-transect, on the face parallel with line-transect direction, to calculate different N values, as the number of times crossing with blade.
Definition P
nfor line-transect through whole cloud data time, with the possibility of crossing n time of blade.P
0what expression line-transect passed through is all space, and summation exponent is 0.By solving the mean value of all line-transects through N during vegetation, can in the hope of the mean value (m) of line-transects all in whole cloud data number of times crossing with blade and variance (σ
2).This number of times intersected not is actual blade point cloud density, but projects to the projection in the plane vertical with line-transect direction.Variance (the σ of every bar line-transect
2the relative change of)/average (m) can reflect the distribution situation of blade at real space.The Leaf positional distribution of isolated tree or standing forest can change (σ relatively according to it
2/ m=1, > 1, and < 1) be divided into three kinds of situations accordingly: regular distribution, stochastic distribution and Assembled distribution.
Line sampling analysis is the key calculating whole canopy and differing heights section extinction coefficient, is conducive to a cloud density, radiation flux and the isoparametric acquisition of radiation profiles situation simultaneously.
(5), when sun incident light pitch angle (θ) is fixing, averaging projection's coefficient of kth layer section is calculated.When only studying the sun incident light in r (θ, a β) direction, the projection coefficient G of that is kth layer section
kr () refers to the projection coefficient in fixing r (θ, β) direction.When not considering incident light position angle, and k layer averaging projection coefficient G when pitch angle is θ
k(θ) be, by the integral and calculating of azimuthal angle beta on [0,2 π]:
(6) projection coefficient under any given incident ray is calculated, i.e. extinction coefficient.First consider to cut into slices with fixed-direction r (θ, β), complete after three dimensional network formats at cloud data, all three-dimensional point clouds are all enclosed in three-dimensional border, generate section and the line-transect of horizontal and vertical.If all sections are parallel with direction r (θ, β), so all line-transects are also parallel to direction r (θ, β), and namely the direction of the longitudinal axis represents this direction.Each volume elements can build a plane perpendicular to this main shaft, and all sampling points can project in this plane.In three-dimensional mesh frame, this projecting plane be two volume elements borders perpendicular to line-transect direction it.If the sampling point number comprised in each non-NULL volume elements is n:
If a. n=1, the square of each two dimension is with user's sampling interval for the length of side, then sampling point represents the center of this square leaf area.If sampling interval is s, then leaf area area is s × s.Projection coefficient is take Sampling Distance as the area (i.e. s × s) of the length of side, with the area ratio of length (the l) × width (w) of volume elements.
If b. n=2, can build a line-transect to represent leaf area, projected area of blade is that the projected length of this line-transect is multiplied by foursquare unit area.Projection coefficient is the line-transect length ratio after projection and before projection.
If c. n >=3, first detect whether all points all on a face or a line.If on same line-transect, then these points are decomposed (n=2) on less yardstick.If on the same face, then build a triangle and represent leaf area, projected area of blade is calculated by the projection coordinate on three summits.Three projection coordinates are set to (x
1, y
1), (x
2, y
2), (x
3, y
3), leg-of-mutton projected area A
pi.e. projected area of blade, by following matrix computations:
If the institute d. in volume elements is a little not coplanar or on one wire, then the convex closure that structure one is three-dimensional, namely the half of convex closure surface area represents actual blade area (A).Then, by all spot projections in the plane parallel with line-transect, set up the convex closure of two dimension with these points, namely its area represents the blade area (A of projection
p)
In sum, projection coefficient A
p/ A is calculated by non-NULL volume elements.Kth layer is perpendicular to the projection coefficient G of incident light
kr () can by following formulae discovery:
Wherein N is total number of kth layer section non-NULL volume elements, and k is the number of plies of section.
Obtain G
kr, after (), substitution formula (2), obtains averaging projection's coefficient of each slicing layer, the projection coefficient (i.e. extinction coefficient) of whole canopy is the summation of each layer section projection coefficient.
Compared with prior art, Advantages found of the present invention exists: laser radar technique provides effective technological means for obtaining Forest Canopy structural parameters from three-dimensional perspective, indirect observation is carried out in conjunction with computational geometry method, compared with conventional observation means, workload is little, without the need to contact observation, do not destroy canopy structure and radiation characteristic, there is objective efficient accurate feature; Develop the method extracting three-dimensional structure and biophysics diversity information from laser radar data, by the Concentration Changing Pattern characterization of blade.
Concrete beneficial effect is as follows:
The three dimensional point cloud that the present invention utilizes laser scanner to obtain, calculates the extinction coefficient of Forest Canopy based on volume elements, provides a kind of indirectly without the need to the method for the observation Forest Canopy biophysical parameters of contact.The present invention keeps sunshine incident along longitudinal axis direction above tree crown by rotating cloud data, carry out sunshine in simulating reality situation and irradiate the sight of tree crown in different angles, not only easy but also efficient, and any harmful effect can not be caused to forest structure and radiation characteristic.The present invention not only can calculate the extinction coefficient of canopy entirety, and can also calculate the extinction coefficient of tree crown differing heights section, this is conducive to studying light radiation retaining and distribution mechanism in canopy inside further, and the research of other biological physical parameter.The present invention observes from three dimensions Forest Canopy mechanism, its key utilizes geometric projection technology that three dimensional point cloud is converted to two-dimensional grid image, calculate the extinction coefficient of canopy differing heights plane from different directions, not only greatly improve estimation precision, and provide bulk information for the research of radiation transmission mechanism of canopy inside.
Practical application shows, the invention provides the effective ways of indirect observation Forest Canopy extinction coefficient, is no matter the extinction coefficient of individual plant trees or forest sample prescription canopy, all can directly uses this method to try to achieve.The method overcome classic method and need spend plenty of time and a large amount of manpower and materials, affect Forest Canopy architectural characteristic, and the defect that error is large.Improve the efficiency of vegetation biophysical parameters estimation, enhance popularization and the validity of three-dimensional laser scanning technique application.The resource environment research project such as forest inventory investigation, vegetation ecological remote sensing can be served better.
Four, accompanying drawing explanation
Fig. 1 is schematic flow sheet of the present invention;
Fig. 2 is traditional blade angle and space distribution observation instrument;
Fig. 3 is voxel data structural representation and dropping cut slice schematic diagram
A. two independent volume elements, and determine length three parameters of its size;
B. the 3 d grid space of 2 × 2 × 2;
C. the three-dimensional space grid schematic diagram of volume elements structure;
D. based on the some cloud dropping cut slice algorithm schematic diagram of volume elements structure;
Fig. 4 is the three dimensional point cloud of a strain North America pesudotsuga taxifolia;
Fig. 5 is that three dimensional network is formatted and point cloud slicing schematic diagram
A. for the some cloud dropping cut slice algorithm schematic diagram based on volume elements structure of individual plant North America pesudotsuga taxifolia;
B. volume elements three-dimensional space grid (5 × 5 × 5 volume elements) schematic diagram of monolayer slices;
Fig. 6 is the line sampling schematic diagram of three dimensional point cloud on the basis of three-dimensional network of higher
A. the extraction of " line sampling " (in figure red rectangular parallelepiped) and analysis;
B. the transversal section of sample is extracted in line sampling;
C. the histogram analysis of sample is extracted in line sampling.
Fig. 7 is single volume elements inner vanes extinction coefficient computing method schematic diagram
A. single volume elements inner vanes three-dimensional point cloud schematic diagram;
B. blade 3-D out inclusion fruit and face are expressed;
C. blade 3-D out inclusion fruit and point, line express;
D. project the in the horizontal plane two-dimentional convex hull computation result of point set and face of blade is expressed.
Fig. 8 is the point cloud slicing layer extinction coefficient profile feature schematic diagram of 14m-16m height
A. this slicing layer point cloud distribution schematic diagram;
B. this slicing layer three-dimensional extinction coefficient spatial distribution characteristic schematic diagram;
C. this slicing layer two-dimensional points cloud density spatial distribution feature schematic diagram;
D. this slicing layer two dimension extinction coefficient spatial distribution characteristic schematic diagram.
Five, embodiment
Below by way of example, the present invention is further explained:
With strain North America pesudotsuga taxifolia (Douglas-fir) for research object (height of tree is about 25m), use Three Dimensional Ground laser scanner Leica ScanStation 2 (its parameter is as shown in table 1) and high-precision GPS, carry out the collection of three dimensional point cloud in a side of tree, sampling interval is 2cm.Manual removably millet cake cloud and other noise spot clouds, obtain the three dimensional point cloud of individual plant North America pesudotsuga taxifolia, as shown in Figure 4.
Table 1 three-dimensional laser scanner Leica ScanStation 2 parameter
Obtaining the cloud data of pesudotsuga taxifolia and after pre-service, as shown in Figure 1, adopt computational geometry technology to process three dimensional point cloud, the first step is that three dimensional network is formatted, and second step is the point cloud slicing based on volume elements, and the 3rd step is line sampling analysis.
According to technical scheme steps (2), carry out gridding to cloud data, set up voxel data structure, each voxel size is 0.5m × 0.5m × 1m.As shown in accompanying drawing 5 (b), for volume elements three-dimensional space grid (5 × 5 × 5 volume elements) schematic diagram of monolayer slices, point Yun Yanse in figure represents differing heights, shown some cloud be highly be 17 to 18 meters in accompanying drawing 5 (a) between some cloud.
Cloud data after formatting to three dimensional network is cut into slices, as the level point cloud Slicing Algorithm schematic diagram based on volume elements structure that accompanying drawing 5 (b) is for a strain North America pesudotsuga taxifolia, grey is 7 slice plane of level, and the different colours of some cloud represents different height.In order to simulated solar irradiation is irradiated to the situation of tree crown from different directions, we sun incident light is fixed on parallel with Z axis directly over, by rotating the cloud data of pesudotsuga taxifolia, carry out the change of simulated solar incident light and tree crown relative angle, to calculate the projection coefficient under arbitrarily angled incident light.
According to technical scheme steps (4), the cloud data that three dimensional network is formatted is carried out line sampling extraction and analyzed.We carry out the line sampling extraction and analysis of vertical direction to pesudotsuga taxifolia cloud data, as shown in accompanying drawing 6 (a), red rectangular parallelepiped is " line sampling ", accompanying drawing 6 (b) is the transversal section of line sampling extraction sample, accompanying drawing 6 (c) is the histogram analysis of line sampling extraction sample, and the cloud data between visible 14m-18m is maximum.
For describing the extinction coefficient computing method of single volume elements inner vanes better, be described below for great Ye maple blade, as shown in Figure 7,7 (a) is the three-dimensional point cloud of maple blade.According to d in technical scheme steps (6), a three-dimensional convex closure is built to blade point cloud, as shown in accompanying drawing 7 (b), for the result of calculation of convex closure and face are expressed.The result of calculation that accompanying drawing 7 (c) is convex closure and point, line are expressed.Calculate the surface area of three-dimensional convex closure, namely the half of its surface area represents actual blade area (A).Then three-dimensional point cloud is projected to (namely vertical with Z axis, parallel with XY axle plane) in the plane vertical with sun incident light, set up the convex closure of two dimension with these points, namely its area represents the blade area (A of projection
p), as shown in accompanying drawing 7 (d).A
p/ A i.e. the extinction coefficient of this blade.
According to the algorithm that the present invention proposes, pesudotsuga taxifolia point cloud is analyzed, described in technical scheme steps (5) and (6), obtain some cloud density spatial distribution and the extinction coefficient of each volume elements in differing heights section.Take height as the section at 14m-16m place be example, as shown in Figure 8: Fig. 8 (a) is this slicing layer point cloud distribution schematic diagram, Fig. 8 (b) is this slicing layer three-dimensional extinction coefficient spatial distribution characteristic schematic diagram, and Fig. 8 (c) and 8 (d) are respectively this slicing layer two-dimensional points cloud density and extinction coefficient spatial distribution characteristic schematic diagram.
As can be seen from the above results, the present invention can also provide the three-dimensional information of tree crown leaves density vertical change and certain height horizontal distribution thereof, is that additive method hardly matches.
Claims (2)
1. utilize laser point cloud to calculate a method for three-dimensional Forest Canopy extinction coefficient, it mainly comprises the following steps:
(1) acquisition of the three-dimensional laser point cloud data of Vegetation canopy and pre-service;
(2) three dimensional network of cloud data is formatted: define one with X, Y, Z are the cartesian coordinate system of axle, and cloud data is divided into limited zonule, set up data structure based on volume elements, each volume elements by growing 1, wide w, high h tri-parameters determine its size;
(3) based on the point cloud slicing algorithm of volume elements structure: after the three dimensional network process of formatting terminates, cloud data is divided into multiple sections in direction in length and breadth, and cloud data is the superposition of direction section in length and breadth; All volume elements are set to (i, j, k), wherein i=1, and 2 ..., m; J=1,2 ... n; K=1,2 ..., p; Work as k=1, i and j is the arbitrary value in given area, be then expressed as first cross section all volume elements; When direct sunlight is injected from zenith direction, parallel with Z-direction; By point of rotation cloud, the change of the relative position of approximate simulation incident ray and Forest Canopy, some cloud level 0 °-360 °, vertical 0 °-90 ° cut into slices, be called directivity section;
(4) line sampling analysis: blade space distribution is in a slice analyzed by the line method of sampling, in every bar line-transect, the N number of number of volume elements of non-NULL represents the line-transect number of times crossing with blade, and N meets stochastic distribution; Definition P
nfor the line-transect parallel with sun incident light direction through whole cloud data time, with the possibility of crossing n time of blade; P
0what expression line-transect passed through is all space, and summation exponent is 0; By solving the mean value of all line-transects through N during vegetation, try to achieve mean value m and the variances sigma of the number of times crossing with blade of all line-transects in whole cloud data
2; The variances sigma of every bar line-transect
2the relative change of/average m reflects the distribution situation of blade at real space; The Leaf positional distribution of isolated tree or standing forest changes σ relatively according to it
2/ m=1, > 1 and < 1 are divided into three kinds of situations accordingly: regular distribution, stochastic distribution and Assembled distribution;
(5) when sun incident light tiltangleθ is fixed, averaging projection's coefficient of kth layer section is calculated: projection coefficient Gk (r) of kth layer section refers to the projection coefficient in fixing r (θ, β) direction; When not considering incident light position angle, and kCeng averaging projection coefficient G when pitch angle is θ
k(θ) be, by the integral and calculating of azimuthal angle beta on [0,2 π]:
(6) projection coefficient under any given incident ray is calculated, i.e. extinction coefficient: by direction r (θ, sun incident light β) is fixed as parallel with Z axis, the cloud data that relative position according to incident light and canopy rotates is cut into slices, generates section and the line-transect of horizontal and vertical; The sampling point number comprised in each non-NULL volume elements is n
If a. n=1, the square of each two dimension is with user's sampling interval for the length of side, then sampling point represents the center of this square leaf area; If sampling interval is s, then leaf area area is s × s; Projection coefficient is: the area ratio taking Sampling Distance as the area of the length of side and length 1 × width w of s × s and volume elements;
If b. n=2, build a line-transect and represent leaf area, projected area of blade is that the projected length of this line-transect is multiplied by foursquare unit area; Projection coefficient is the line-transect length ratio after projection and before projection;
If c. n>=3, first detect whether all points all on a face or a line; If on same line-transect, then these points are decomposed on less yardstick, i.e. n=2; If on the same face, then build a triangle and represent leaf area, projected area of blade is calculated by the projection coordinate on three summits; Three projection coordinates are set to (x
1, y
1), (x
2, y
2), (x
3, y
3), leg-of-mutton projected area A
pi.e. projected area of blade, by following matrix computations:
If the institute d. in volume elements is a little coplanar or on one wire, then build a three-dimensional convex closure, namely the half of convex closure surface area represents actual blade area A; Then, by all spot projections in the plane parallel with line-transect, set up the convex closure of two dimension with these points, namely its area represents the blade area A of projection
p;
Projection coefficient A
p/ A is calculated by non-NULL volume elements;
Kth layer is perpendicular to the projection coefficient G of incident light
kr () is by following formulae discovery:
Wherein N is total number of kth layer section non-NULL volume elements, and k is the number of plies of section;
Obtain G
kr after (), substituting into formula (1), obtain averaging projection's coefficient of each slicing layer, the projection coefficient of whole canopy, i.e. extinction coefficient, is the summation of each layer section projection coefficient.
2. a kind of method utilizing laser point cloud to calculate three-dimensional Forest Canopy extinction coefficient according to claim 1, its feature is in step (1), described three-dimensional laser point cloud data is the forest cover canopy point cloud obtained by Three Dimensional Ground laser scanner, wherein contain the energy information that the scanning space geometry of impact point and laser beam are rebounded, and the locus coordinate information of each point, image mosaic is carried out to the some cloud obtained, and manual removably millet cake cloud, as the data source extracting canopy structure information.
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