CN109033562A - Calculation method of the blade two to reflected value under a kind of rolled state - Google Patents

Abstract

The invention discloses blades two under a kind of rolled state to the calculation method of reflected value, comprising: establishes crimping blade appearance model and global coordinate system；The parameter information of light source and probe is set；The blade of curling is divided into micro- plane, extracts the center point coordinate of each micro- plane；Utilize Ray Tracing Algorithm, it is tracked from probe direction of visual lines, contribution of each micro- plane to probe energy is calculated, then by the energy of all micro- plane reflections and transmission in integral beta probe visual field, to obtain the energy of entirely the pop one's head in blade reflection and transmission that receive；Calculate the energy for the lambert's body entirely popped one's head in visual field under lambert's concrete conditions in the establishment of a specific crime；The energy that energy and lambert's body reflection of blade reflection and transmission are received by popping one's head in, calculates the BRDF of blade.It present invention introduces micro- plane and Ray Tracing Algorithm, solves the BRDF calculation method of blade under the conditions of curling, the BRDF model extension of plane has been arrived into three-dimensional space.

Description

A Calculation Method of Bidirectional Reflection Value of Blade in Curled State

technical field

The invention relates to the technical field of blade optical measurement, in particular to a method for calculating the two-way reflection value of a blade in a curled state.

Background technique

The leaf is the main organ that receives photosynthetically active radiation in the range of 400nm-800nm, and its photosynthetic properties vary with wavelength and measurement configuration. Leaf biochemical and anatomical information can be obtained through the spectrum and direction distribution of incident light and first incident light. Most papers focus on correlating the reflectance and transmission of the leaf spectrum with the content of chlorophyll, moisture, cellulose, nitrogen, etc. From such observations, Allen et al. (1969) estimated the effective reflectance index of maize through a geometric optics-based plate model. Jacquemoud and Baret (1990) further developed the PROSPECT model, which can more accurately estimate the water, chlorophyll and dry matter content of different types of leaves. Woolley (1971) was one of the first researchers interested in the spatial distribution of light reflected from philodendron, corn, and soybean leaves. He distinguished diffuse reflection from specular reflection and pointed out that specular reflection is different from the usual reflection in most canopies. The assumptions in the models vary widely. Breece and Holmes (1971) scanned 19 narrow bands and observed that the specular reflection component is relatively more important in the strong absorption range. Finally, Brakke et al. (1989) related the characteristics of the diffuse and specular components to the leaf anatomy, but their measurements were limited to a single band.

Previous scholars have emphasized in the study of leaf optical properties that if we want to distinguish specular reflection and diffuse reflection components, we need to improve the connection between biophysical parameters and remote sensing data. Therefore, it is closely related to distinguishing between these two components in the reflection of the leaf, since they carry different information. On the one hand, the diffuse reflection component is caused by multiple scattering of light inside the leaf, and its angular distribution is isotropic, so its spectral variation is determined by the biochemical information of the leaf, so it can be used to estimate the leaf group content. On the other hand, the specular component is due to a single regular scattering at the leaf surface and thus is determined by the biophysical properties of the surface. Its magnitude and angular distribution allow estimation of the refractive index and the roughness of the epidermis. In contrast, leaf components like chlorophyll do not, or have very little, influence on the spectral changes in specular reflection in the visible range.

Since the bidirectional reflectance (BRDF) has been measured, many models have been proposed to fit them. Ward (1992) and Brakke et al. (1989) presented simple equations for empirical parameter estimation. To further interpret the signal, a physics-based model is necessary. Nicodemus et al. (1977) described the concept of bidirectional reflection (BRDF) and bidirectional transmission (BRTF) in detail by collecting the spectrum and reverse changes of optical properties. It is now widely used in the fields of remote sensing and computer-generated imagery. Most surface BRDF models with physical input parameters can be viewed as a summation of a specular and a diffuse component. The simplest way to describe the diffuse component is to assume that the light is modeled as an isotropic Lambertian body, which is, of course, an idealized behavior. Torrance and Sparrow (1967) laid the foundation for more realistic BRDF models of surfaces. They regard the surface as a composition of many tiny surfaces whose width is much wider than the wavelength, and they apply the laws of geometric optics to obtain the corresponding BRDF. Cook and Torrance (1981) continued this work with Oren and Nayar (1995), obtaining accurate expressions for the specular and diffuse components. Covaerts et al. (1966) and Baranoski and Rokne (2004) used ray-tracing techniques to build a model for use. However, the high computational requirements hinder the inversion of this model, and it is only suitable for the BRDF calculation of flat blades.

Therefore, the present invention introduces the micro-plane method and extends the plane BRDF model to a three-dimensional space model, thereby being able to calculate the BRDF of the blade in the curled state, and introduces a ray tracing algorithm to simulate the light transmission process from the probe in reverse, greatly reducing the calculation Quantities, solved the BRDF calculation method of the blade under the curling condition, provided a set of efficient calculation method for the spatial distribution characteristics of the curled blade's reflection of incident light in the hemispherical direction, and can use this method to invert the blade surface attribute parameters.

Contents of the invention

At present, the BRDF simulation of the blade is mostly limited to the plane model, and the BRDF simulation of the blade in the curled state is rarely discussed. The purpose of the present invention is to overcome the limitation of the existing BRDF model and provide a method for calculating the bidirectional reflectance (BRDF) value of the blade in the curled state.

The present invention introduces the microplane algorithm to extend the BRDF model of the plane to the three-dimensional space model, so that the BRDF of the blade in the curled state can be calculated, and a ray tracing algorithm starting from the reverse direction of the probe is introduced to simulate the reflection and transmission of light between the microplanes of the blade The process greatly reduces the calculation amount of the blade BRDF simulation starting from the incident light direction, solves the BRDF calculation method of the blade under the curling condition, and this method has a high consistency with the measured BRDF of the curling blade. Therefore, this method can also be used to invert the attribute parameters of the curled blade surface and BRDF.

A method for calculating blade bidirectional reflectance (BRDF) values in a curled state, comprising the following steps:

Step 1, establish the curly blade shape model and the global coordinate system;

Step 2. Set the parameter information of the light source and probe;

Step 3, dividing the curled blade into a plurality of microplanes, and extracting the center point coordinates of each microplane;

Step 4. Use the ray tracing algorithm to track from the line of sight of the probe, and calculate the contribution of each microplane to the energy of the probe. The energy received by the probe includes the energy reflected and transmitted by the blade, and then integrate all the microplanes in the field of view of the probe Reflected and transmitted energy, thus obtaining the reflected and transmitted energy of the blade received by the whole probe;

Step 5, calculating the energy reflected by the Lambertian body in the entire probe field of view under the Lambertian body condition;

Step 6. Calculating the bidirectional reflectance (BRDF) value of the curled leaf.

In step 1, the curled leaf shape model and the global coordinate system are established, including:

Taking the center of the blade as the origin O, the long axis as the Y axis, the short axis as the X axis, and the normal that passes through the origin of the XY plane as the Z axis, a global Cartesian coordinate system for the entire simulation process is established, and the blade is abstracted into a three-dimensional space. Curly oval. The leaf is abstracted into an ellipse, and the curled leaf is abstracted into an ellipse curled in three-dimensional space, and the degree of curling, the length of the major axis and the length of the minor axis of the leaf are set.

In step 2, set the parameter information of the light source and probe, including:

Set the position information of the light source, the intensity of the light source, and the incident direction of the light, and set the probe field of view angle, the center direction of the probe field of view, and the position parameters. The outgoing direction of the light is also the center direction of the probe field of view. In the Cartesian coordinate system, the incident direction of the light and the center direction of the probe's field of view can be represented by a unit vector.

In step 3, the curled blade is divided into multiple microplanes (preferably 1/16mm ² ), and the center point coordinates of each microplane are extracted, specifically including:

Divide the curly leaves into microplanes of 1/16mm2, the distance between the center points of adjacent microplanes is 1/4mm, the leaves are curled, the symmetrical plane is the ^YOZ plane, and the intervals between the X-axis coordinates of the center points of adjacent microplanes are equal , is 1/4mm; the Y-axis coordinate interval of the adjacent micro-plane center points is not equal, and it is obtained by an iterative method; Coordinates of the center point of the leaf microplane.

In step 4, the contribution of each microplane to the probe energy is calculated, including:

First, it is necessary to judge whether to use the two-way reflection distribution function or the transmission distribution function, and whether to use the light iteration algorithm, as follows:

1. If the line of sight is on the front of the blade and the light is on the back of the blade, you need to use the transmission distribution function without considering the iteration;

2. If the line of sight is on the back of the blade and the light is on the front of the blade, you need to use the transmission distribution function without considering the iteration;

3. If the line of sight is on the back of the blade and the light is on the back of the blade, you need to use the bireflection distribution function without considering iterations;

4. If the line of sight is on the front of the blade and the light is on the front of the blade, this is a reflection situation. It is necessary to use the iterative algorithm of light and the bidirectional reflection distribution function. When the iterated light is attenuated to less than the initial light source intensity by 1×10 ^-3 after transmission or reflection When , the iteration is stopped, and the energy obtained by this optical path iteration is taken as the contribution of the microplane to the probe energy.

In order to avoid the huge amount of calculation of ray tracing from the incident direction of the light source, the reverse ray tracing algorithm is used. Here, the ray tracing is carried out from the direction of the line of sight, and the light path is regarded as being emitted from the direction of the line of sight. Finally, through iterative calculation, each Then, by integrating the reflected and transmitted energy of all microfacets in the entire probe field of view, the obtained energy in the entire probe is obtained.

Step 5, calculating the energy reflected by the Lambertian body in the entire probe field of view under the Lambertian body condition, specifically including;

Divide the Lambertian whiteboard into 1/16mm ² microplanes, extract the center point coordinates of each microplane, and calculate the energy reflected by the Lambertian body in the entire probe field of view through the bidirectional reflection distribution function and integral calculation.

Step 6, calculating the bidirectional reflection (BRDF) value of the curled blade, specifically including:

The ratio of the energy reflected and transmitted by the blade received by the probe obtained in step 4 to the energy reflected by the lambertian body in the field of view of the probe obtained in step 5 obtains the reflectivity of the blade, and the reflectance ratio π is obtained at a fixed Blade Bidirectional Reflectance (BRDF) values in the incident and reflected directions.

Compared with the prior art, the present invention has the advantages of:

1. It can accurately simulate the BRDF of curled leaves, so that the method can be used to directly calculate the BRDF distribution characteristics of the leaves in the hemispherical direction, reduce the workload of observing the BRDF distribution characteristics of curled leaves through experiments, and effectively reduce the observation cost;

2. Using the micro-plane algorithm, the planar BRDF model is extended to a three-dimensional space model, making the calculation closer to the natural shape of the blade;

3. Introduce the ray tracing algorithm reversed from the probe to simulate the reflection and transmission process of light between the micro-planes of the blade, which greatly reduces the calculation amount of the blade BRDF simulation starting from the direction of the incident light.

Description of drawings

Fig. 1 is the flow chart of the calculation method of blade bidirectional reflectance (BRDF) value under the curling state of the present invention;

Figure 2 is the BRDF distribution diagram of the measured curly blade in the hemispherical direction;

Fig. 3 is a BRDF distribution diagram of simulated curled blades in the hemispherical direction using the method of the present invention.

Detailed ways

The present invention will be further described below in conjunction with specific drawings and embodiments.

As shown in Figure 1: the present invention is a method for calculating the blade BRDF in a curled state, and the specific calculation method includes the following steps:

Step 1, establishing a blade shape model and a global coordinate system;

Specifically, set the degree of curling, the length of the major axis and the length of the minor axis of the blade, take the center of the blade as the origin O, the major axis as the Y axis, the minor axis as the X axis, and the normal line passing through the origin of the XY plane as the Z axis to establish The global Cartesian coordinate system of the whole simulation process abstracts the blade into an ellipse curled in three-dimensional space.

Step 2. Set the parameter information of the light source and probe.

Specifically, dichroism is mainly about the reflection of incoming and outgoing light in different directions. The difference in radiance in the outgoing direction is due to the difference in angle between the incident light and the outgoing light. Here, set the position information of the light source, the intensity of the light source, and the incident direction of the light, and set the probe field of view angle, the center direction of the probe field of view, and the position parameters. The center direction of the probe field of view is also the outgoing direction of the light. In the Cartesian coordinate system, the incident direction of the ray and the direction of the center of the field of view can be represented by a unit vector.

Step 3, dividing the curled blade into ¹ /16mm microplanes, extracting the center point coordinates of each microplane;

In the implementation of the present invention, the curled blade is divided into 1/16mm ² microplanes, and the center point coordinates of each microplane are extracted. The distance between the center points of adjacent microplanes is 1/4 mm. Because the blades are curled and the symmetry plane is the YOZ plane, the intervals between the X-axis coordinates of the center points of adjacent microplanes are equal, which is 1/4mm. However, the Y-axis coordinate intervals of the center points of adjacent microplanes are not equal, and need to be obtained through an iterative method. After obtaining the Y-axis coordinates of the center point of the microplane, the Z-axis coordinates can be obtained through the blade curl equation. Thus, the coordinates of the center point of each leaf microplane are obtained.

Step 4. Use the ray tracing algorithm to trace from the line of sight of the probe, calculate the contribution of each microplane to the energy of the probe, and then obtain the blade received by the entire probe by integrating the energy reflected and transmitted by the microplane in the field of view of the probe. reflected and transmitted energy;

In the implementation of the present invention, in order to avoid the huge amount of calculation of ray tracing from the incident direction of the light source, a reverse ray tracing algorithm is used. Here, the tracking is performed from the direction of the line of sight, and the light path is regarded as being emitted from the direction of the line of sight. The energy reflected and transmitted by each microfacet within the probe field of view is then integrated by integrating the energy reflected and transmitted by all microfacets within the entire probe field of view to obtain the energy gained within the entire probe. Here, if the center of the microplane of the blade is within the field of view of the probe, it is considered that there is an intersection between the center of the microplane of the blade and the line of sight, and the normal of the tangent plane where the intersection is located is calculated. Establish a local coordinate system with the normal of the tangent plane as the z-axis, store the coordinate system in a 3×3 matrix, convert the incident light and outgoing light from the global coordinate system to the local coordinate system, and then judge the line of sight and light on the blade In the case of intersection, judge whether to use the bidirectional reflection distribution function or the transmission distribution function, and judge whether to use the ray iteration algorithm.

Mainly divided into the following situations:

1. If the line of sight is on the front of the blade and the light is on the back of the blade, this is a transmission situation. Since the light intensity contributed by the transmission is very small, it is not necessary to consider the iteration of the light, but only the transmission distribution function.

2. If the line of sight is on the back of the blade and the light is on the front of the blade, this is a transmission situation, and only the transmission distribution function needs to be considered.

3. If the line of sight is on the back of the blade and the light is on the back of the blade, this is a reflection situation. Only the two-way reflection distribution function needs to be considered. Since the back of the blade is convex, there is no need to consider the mutual reflection between the micro-planes of the blade, so there is no need to consider Iteration of rays.

4. If the line of sight is on the front of the blade and the light is on the front of the blade, this is a reflection situation, and the iterative algorithm of light and the bidirectional reflection distribution function need to be used. When the iterated light decays to less than 1×10 ^-3 intensity of the initial light source through transmission or reflection, the iteration is stopped, and the energy obtained by this light path iteration is taken as the contribution of the microplane to the energy of the probe.

The transmission and reflection in the process of ray tracing are judged, and the energy of the light reflected and transmitted out of the blade microplane is calculated by using the transmission and reflection distribution functions respectively.

Specifically, for the calculation of energy in the case of reflection, the radiance (R) of the light reflected by the microplane of the blade can be obtained by multiplying the irradiance (I) by the bidirectional reflection distribution function (BRDF), as shown in formula (1) :

Among them, λ, θ _s , θ _v and They are the wavelength of the incident light, the incident zenith angle, the incident azimuth angle, the line-of-sight zenith angle and the line-of-sight azimuth angle. Generally, the incident azimuth angle By convention, it is set to 0. The BRDF function of the blade is also related to the refraction coefficient and roughness coefficient of the blade. The calculation of BRDF can be assumed to be the sum of diffuse reflection and specular reflection, called BRDF _diff and BRDF _spec respectively, as shown in formula (2)

BRDF＝BRDF _diff +BRDF _spec (2)

Among them, the diffuse reflection component represents a small part of the reflected light, it is not a single specular reflection of the blade surface. We assume that it behaves as a diffuse Lambertian and strongly depends on the wavelength, so the BRDF _diff can be written as:

where 1/π is the BRDF for perfect Lambertian scattering and k _L (λ) is the Lambertian coefficient with wavelength λ.

For the specular part, the BRDF _spec can be expressed in the following form:

Among them, F(n,θ _a ) is the Fresnel factor, and the Fresnel factor is determined by the refractive index n of the leaf surface material and the incident angle θ _a in the normal line of the micro-plane and the direction of the incident light, and α represents in a lower scale The inclination angle of the tiny plane, n is the refraction coefficient of the blade, and σ is the roughness coefficient.

Specifically, for the energy calculation of the transmission case, the irradiance (I) of the incident light can be converted into the radiance (R) of the transmitted light through the transmission distribution function, as shown in formula (5):

Among them, the transmission distribution function is shown in the following formula (6):

Among them, τ is the transmittance parameter, and k _L (λ) is the Lambertian parameter.

Step 5, calculating the energy reflected by the Lambertian body in the field of view of the probe;

Specifically, the Lambertian whiteboard is divided into 1/16mm ² microplanes, and the center point coordinates of each microplane are extracted. The distance between the center points of adjacent microplanes is 1/4 mm. Because the whiteboard is horizontal, and the horizontal plane is the XOY plane, the Z-axis coordinates of the center points of the micro-planes are all 0, and the distance between the X-axis coordinates of the adjacent micro-plane centers is 1/4mm, and the distance between the center points of the adjacent micro-planes is 1/4mm. The spacing of the Y-axis coordinates is also 1/4mm. In the actual measurement, the reflectance of the leaves observed within the probe's field of view range is that the light intensity received by the probe from the leaves is greater than the light intensity received by the probe from the whiteboard within the same field of view range, so a whiteboard should be simulated in the program , and deal with the blades of the model accordingly. Since the whiteboard is a Lambertian body, the two-way reflection distribution function of the whiteboard is shown in formula (3).

Step 6. Calculate the BRDF of the curled blade in the direction of the whole hemisphere.

In the implementation of the present invention, the ratio of the blade reflection and transmission energy received by the probe obtained in step 4 to the whiteboard energy received by the probe obtained in step 5 obtains the reflectance of the blade, and the ratio of reflectance π obtains the fixed The vane BRDF values in the incident and reflected directions are then plotted for the vane's BRDF distribution across the hemisphere. Figure 2 is the measured BRDF of the blade in the hemispherical direction under the condition that the incident light source is at a zenith angle of 40° and an azimuth angle of 0°. The asterisk indicates the position of the light source, and the black dot indicates the position observed by the probe. Fig. 3 uses the method of the present invention to simulate the BRDF of the blade in the hemispherical direction under the condition that the incident light source is at a zenith angle of 40° and an azimuth angle of 0°. The asterisk represents the position of the light source, and the black dot represents the position observed by the probe. Comparing Fig. 2 and Fig. 3, it can be seen that the BRDF of the curled blade simulated by the present invention in the hemispherical direction has a high consistency with the measured BRDF of the curled blade in the hemispherical direction.

Claims (6)

1. calculation method of the blade two to reflected value under a kind of rolled state, which comprises the following steps:

Step 1 establishes crimping blade appearance model and global coordinate system；

Step 2, the parameter information that light source and probe are set；

The blade of curling is divided into multiple micro- planes by step 3, extracts the center point coordinate of each micro- plane；

Step 4, using Ray Tracing Algorithm, tracked from probe direction of visual lines, calculate each micro- plane to probe energy Contribution, the energy received of popping one's head in includes the energy of blade reflection and transmission, then by all micro- in integral beta probe visual field The energy of plane reflection and transmission, to obtain the energy of entirely the pop one's head in blade reflection and transmission that receive；

Step 5, the energy for calculating lambert's body reflection in visual field of entirely popping one's head under lambert's concrete conditions in the establishment of a specific crime；

Step 6 calculates the two of crimping blade to reflected value.

2. calculation method of the blade two to reflected value under rolled state according to claim 1, which is characterized in that step 1 In, crimping blade appearance model and global coordinate system are established, is specifically included:

Using blade center as origin O, long axis is Y-axis, and short axle is X-axis, and the normal for crossing X/Y plane origin is Z axis, it is established that entire Blade is abstracted into an ellipse in three-dimensional space curling by the global cartesian coordinate system of simulation process.Blade is abstracted into ellipse Circle, crimping blade are abstracted into the ellipse of three-dimensional space curling, set the crimpness, long axis length and minor axis length of blade.

3. calculation method of the blade two to reflected value under rolled state according to claim 1, which is characterized in that step 2 In, the parameter information of light source and probe is set, is specifically included:

Be arranged the location information of light source, the incident direction of the intensity of light source and light and be arranged probe field angle, probe visual field in Heart direction and location parameter, the exit direction of light that is to say probe field of view center direction.In cartesian coordinate system, list can be used Bit vector indicates incident direction and the probe field of view center direction of light.

4. calculation method of the blade two to reflected value under rolled state according to claim 1, which is characterized in that step 3 In, the blade of curling is divided into multiple micro- planes, the center point coordinate of each micro- plane is extracted, specifically includes:

The blade of curling is divided into 1/16mm²Micro- plane, the distance of adjacent micro- planar central point is 1/4mm, and blade is curling, The plane of symmetry is YOZ plane, and it is 1/4mm that the interval of adjacent micro- planar central point X axis coordinate, which is equal,；Adjacent micro- planar central Point Y axis coordinate interval be not it is equal, obtained by the method for iteration；After obtaining micro- planar central point Y axis coordinate, pass through blade Curling equation obtains Z axis coordinate, to obtain the center point coordinate of the micro- plane of each blade.

5. calculation method of the blade two to reflected value under rolled state according to claim 1, which is characterized in that step 4 In, contribution of each micro- plane to probe energy is calculated, is specifically included:

First to judge use distribution of bi directional reflectance function still to transmit distribution function, decide whether using light iteration Algorithm, specific as follows:

If 1. sight in face of blade and light needs not having to consider iteration using transmission distribution function in vacuum side of blade；

If 2. sight in vacuum side of blade and light needs not having to consider iteration using transmission distribution function in face of blade；

3. if needing not having to consider using distribution of bi directional reflectance function sight is in vacuum side of blade and light is in vacuum side of blade Iteration；

If this is reflection case 4. sight is in face of blade and light is in face of blade, need to calculate using the iteration of light Method and distribution of bi directional reflectance function, when the light of iteration is decayed to by transmission or reflection less than primary light source intensity 1 × 10^-3 When, then stop iteration, contribution of the energy that this optical path iteration is obtained as micro- plane to probe energy.

6. calculation method of the blade two to reflected value under rolled state according to claim 1, which is characterized in that step 6, The two of calculating crimping blade specifically include to reflected value:

The entire probe visual field that the energy and step 5 of the blade reflection and transmission that are received by the probe that step 4 obtains obtain The ratio between the energy of interior lambert's body reflection has obtained the reflectivity of blade, and π has been obtained in fixed incidence and anti-on luminance factor Blade two on direction is penetrated to reflected value.