CN101901302A - Light scattering modeling method for complex spatial object - Google Patents

Light scattering modeling method for complex spatial object Download PDF

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Publication number
CN101901302A
CN101901302A CN 201010228868 CN201010228868A CN101901302A CN 101901302 A CN101901302 A CN 101901302A CN 201010228868 CN201010228868 CN 201010228868 CN 201010228868 A CN201010228868 A CN 201010228868A CN 101901302 A CN101901302 A CN 101901302A
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light scattering
spatial object
cross
reflectivity
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蓝朝桢
徐青
孙伟
李建胜
周杨
邢帅
何钰
张衡
施群山
靳国旺
马东洋
王栋
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PLA Information Engineering University
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PLA Information Engineering University
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Abstract

The invention relates to a light scattering modeling method for a complex spatial object, belonging to the technical field of modeling aerospace spatial objects. The method of the invention comprises the following steps: firstly, establishing a light scattering empirical model of a material according to the comprehensive light scattering intensity of the material; obtaining incident sections of the spatial object by parallel projection transformation, and judging and selecting an effective incident section; according to the light scattering empirical model of the material, counting the mean value of the reflectivity of pixels on the drawn effective incident section to obtain the mean reflectivity; calculating the area of the effective incident section according to the proportional relation between the total number of the pixels on the effective incident section and the area of a drawn window; and establishing a light scattering model of the complex spatial object. In the invention, on the basis of considering the incoherent scattering characteristic and coherent scattering characteristic of the material, according to the practical propagation characteristic of rays, complex calculation of a three-dimensional space is projected to a two-dimensional surface, the computer graphics theory is utilized for realizing quick determination of the effective incident section and the mean reflectivity of the section, and the problem of light scattering calculation of the complex spatial object is better solved.

Description

Light scattering modeling method for complex spatial object
Technical field
The present invention relates to light scattering modeling method for complex spatial object, belong to aerospace Target Modeling technical field.
Background technology
The Optical characteristics of extraterrestrial target is the optical detection of target, the prerequisite of identification, and the extraterrestrial target light scattering characteristic is the important content of optical characteristics, is just receiving increasing concern.A lot of scholars have carried out a large amount of research work in this respect, integrate, its method concentrates on following two aspects: the one, regard extraterrestrial target as diffuse reflection Lambert surface by several typical shape, and according to theory of radiation and Lambert cosine law, calculate its illuminance in the space; The 2nd, utilize the accurate bidirectional reflectance distribution function of material print (BRDF) of actual measurement, calculate the light scattering characteristic of target based on the method for physical model.The first method model is simple, and result of calculation and actual conditions differ bigger, can only be used for the estimation of light scattering characteristic; Second method can the accurate Calculation material light scattering characteristic, but obtain, expression and complexity of calculation, limited its application in the engineering field.Existing research work all assumes simple shape with extraterrestrial target mostly, and for the calculating of the light scattering of the extraterrestrial target with complicated geometirc physique, does not all propose good solution.
Summary of the invention
The purpose of this invention is to provide a kind of light scattering modeling method for complex spatial object, to solve the problem of existing complex spatial object modeling method degree of accuracy and computational complexity contradiction.
For achieving the above object, the step of light scattering modeling method for complex spatial object of the present invention is as follows:
(1) according to the comprehensive light scattering intensity of material, sets up material light scattering empirical model;
(2) adopt the parallel projection conversion to obtain the incoming cross-section of extraterrestrial target, and judge and select effective incoming cross-section;
(3) according to material light scattering empirical model, the reflectivity average of pixel obtains average reflectance on effective incoming cross-section that statistics is drawn
Figure 64545DEST_PATH_IMAGE001
(4) according to effective total number of incoming cross-section pixel and the area ratio relation of drawing window, try to achieve effective incoming cross-section area
Figure 612070DEST_PATH_IMAGE002
(5) set up the complex spatial object photon diffusion models
Figure 999189DEST_PATH_IMAGE003
, in the formula
Figure 306674DEST_PATH_IMAGE004
Be the illumination of the sun at the extraterrestrial target place;
Figure 197269DEST_PATH_IMAGE002
Area for effective incoming cross-section; Be the average reflectance on the cross section.
Further, the comprehensive light scattering intensity of material is diffuse reflection component and direct reflection summation in the described step (1), is expressed as
Figure 229259DEST_PATH_IMAGE006
, wherein
Figure 402751DEST_PATH_IMAGE007
Be the diffuse-reflection factor of object, relevant with body surface character;
Figure 600383DEST_PATH_IMAGE008
It is the light intensity of light source;
Figure 568339DEST_PATH_IMAGE009
Be angle of incidence of light;
Figure 602154DEST_PATH_IMAGE010
Be the specularity factor of object, Angle for sight line and reflection direction.
Further, material light scattering empirical model is in the described step (1)
Figure 861502DEST_PATH_IMAGE012
, wherein Be integrated reflectance, be when light with
Figure 521471DEST_PATH_IMAGE009
When the angle is incided on certain material surface,
Figure 771186DEST_PATH_IMAGE014
The ratio of the reflective light intensity on the direction and incident intensity.
Further, the acquisition of space target incoming cross-section is in OpenGL in the described step (2), utilize function glOrtho (l, r, b, t, n, f) finish the parallel projection conversion, function parameter be parallel projection about, up and down with far and near cutting face, with the real area of these calculation of parameter view fields
Figure 943411DEST_PATH_IMAGE015
, (w h) transforms to the screen pixels coordinate with the left side after the projective transformation for x, y, and (x y) is viewport lower left corner coordinate to parameter, and (w h) is window size, gets x=y=0, and then the sum of all pixels of whole display window is to use function glViewport again
Figure 253169DEST_PATH_IMAGE016
Further, described step (2) when drawing incoming cross-section, in GPU sheet unit tinter, is carried out free area and is judged, rejects the cross section point that does not satisfy Rule of judgment; To satisfying the point of free area condition, according to the material properties of material, the cross section unit reflectivity empirical model to each pixel representative in the GPU tinter calculates, and forms the reflectivity distribution plan.
Further, described free area is the part that the energy reflection ray arrives observed ray in incoming cross-section, when light source direction L and observed ray V determine, when the angle of being satisfied with L and V when the normal N of bin dA is all spent less than 90, this face is by irradiate light, and the energy reflection ray is to scope, and the Rule of judgment of this free area is expressed as with inner product of vectors:
Figure 261576DEST_PATH_IMAGE017
Further, the two dimensional image that described reflectivity distribution plan is made of the reflectivity of each pixel on the effective incoming cross-section of extraterrestrial target, with diffuse reflection in the model data and direct reflection parameter is each leg-of-mutton material assignment, in OpenGL sheet unit tinter,, utilize formula according to light source attribute, material properties and geometric relationship
, finish calculating to each pixel reflectivity on the incoming cross-section, after modeling rendering finishes, just constituted the reflectivity distribution plan of whole extraterrestrial target.
Further, average reflectance in the described step (3)
Figure 843179DEST_PATH_IMAGE018
Be reflectivity summation with each pixel on the reflectivity distribution plan, and divided by the valid pixel sum
Figure 323839DEST_PATH_IMAGE019
Obtain.
Further, effective incoming cross-section area in the described step (4) Computing formula as follows:
Figure 411060DEST_PATH_IMAGE020
, wherein valid pixel adds up to
Method of the present invention is on the basis of having considered material non-coherent scattering characteristic and coherent scattering characteristic, according to light actual propagation characteristic, a kind of light scattering modeling method for complex spatial object has been proposed, three-dimensional complicated calculations is projected to two dimensional surface, and utilize Compute Graphics Theory to realize determining fast of effective incoming cross-section and cross section average reflectance, preferably resolve the light scattering computational problem of complex spatial object.
The material light scattering empirical model that the present invention set up comes the representation space target material to have more rationality than the simple diffuse reflection model that adopts, wherein, and diffuse-reflection factor
Figure 943859DEST_PATH_IMAGE007
, specularity factor
Figure 926858DEST_PATH_IMAGE021
, the direct reflection index Relevant with the material self character, can be with the light scattering characteristic of these three parameter approximate expression materials, and, under the approaching situation of effect, simplified expression and complexity of calculation with respect to BRDF method based on physical model, make it more flexible.
Described
Figure 559276DEST_PATH_IMAGE005
For on the free area each
Figure 585001DEST_PATH_IMAGE023
Corresponding target surface infinitesimal
Figure 852034DEST_PATH_IMAGE024
The average of reflectivity because target has complicated configuration, an infinitesimal on the incoming cross-section
Figure 237885DEST_PATH_IMAGE023
May be the little bins of a plurality of target surfaces Projection, and different
Figure 837811DEST_PATH_IMAGE024
Since the material difference, reflectivity Also different, this is
Figure 17567DEST_PATH_IMAGE023
Reflectivity
Figure 540953DEST_PATH_IMAGE013
Determine to have caused difficulty, investigating the communication process of light finds, when a light incides the extraterrestrial target surface, the face of first and ray intersection is for being subjected to solarization face on the light ray propagation direction, thereafter face all can be owing to blocking the generation shade, promptly, have only the face nearest just reflected energy to be had contribution apart from light source for an incident ray, so the present invention
Figure 908480DEST_PATH_IMAGE024
Get the bin nearest, both determined apart from light source
Figure 884526DEST_PATH_IMAGE023
Reflectivity
Figure 612180DEST_PATH_IMAGE013
, prevented effectively that again the dash area that is blocked from participating in calculating.
Description of drawings
Fig. 1 is a complex spatial object light scattering modeling process flow diagram of the present invention;
Fig. 2 is incident, reflection, direction of visual lines synoptic diagram;
Fig. 3 is the direct reflection curve map;
Fig. 4 is a Qiuckbird-2 satellite geometry shape assumption diagram;
Fig. 5 is the observation condition curve map;
Fig. 6 (a) is total incoming cross-section figure;
Fig. 6 (b) is effective incoming cross-section figure;
Fig. 7 is effective incoming cross-section and total incoming cross-section comparison diagram;
Fig. 8 is target reflectivity figure;
Fig. 9 is the target average reflectivity change curve;
Figure 10 is the reflection flux change curve.
Embodiment
The process flow diagram of light scattering modeling method for complex spatial object embodiment of the present invention as shown in Figure 1, step is as follows:
(1) according to the comprehensive light scattering intensity of material, sets up material light scattering empirical model;
(2) adopt the parallel projection conversion to obtain the incoming cross-section of extraterrestrial target, and judge and select effective incoming cross-section;
(3) according to material light scattering empirical model, the reflectivity average of pixel obtains average reflectance on effective incoming cross-section that statistics is drawn
(4) according to effective total number of incoming cross-section pixel and the area ratio relation of drawing window, try to achieve effective incoming cross-section area
Figure 528500DEST_PATH_IMAGE002
(5) set up the complex spatial object photon diffusion models
Figure 257422DEST_PATH_IMAGE003
, in the formula
Figure 42230DEST_PATH_IMAGE004
Be the illumination of the sun at the extraterrestrial target place;
Figure 540207DEST_PATH_IMAGE002
Area for effective incoming cross-section;
Figure 983958DEST_PATH_IMAGE005
Be the average reflectance on the cross section.
1 material light scattering empirical model
No matter be that the extraterrestrial target main body clad material or the light scattering of solar panels generally all exist non-coherent scattering component (claim not only diffuse reflection) and coherent scattering component (but also claiming direct reflection).Therefore, the accurate Calculation of implementation space target light scattering properties, must set up the diffuse reflection and the properties of specular reflection model of extraterrestrial target surfacing.Because light satisfies additivity, therefore, under the prerequisite of the scattering properties on hypothetical target surface and Wavelength-independent, will diffuse and specular light is considered respectively.
1.1 diffuse reflection model
When the diffuse reflection phenomenon appears during to all direction equivalent scatterings in incident light from a complete rough surface.Suppose that the space distribution that diffuses in the material is that according to the Lambert cosine law, reflective light intensity is directly proportional with the incident cosine of an angle uniformly.Therefore, reflective light intensity
Figure 387127DEST_PATH_IMAGE025
Can be expressed as
Figure 269632DEST_PATH_IMAGE026
, in the formula
Figure 559799DEST_PATH_IMAGE007
Be the diffuse-reflection factor of object, relevant with body surface character.
Figure 502347DEST_PATH_IMAGE008
It is the light intensity of light source.
Figure 628697DEST_PATH_IMAGE009
Be angle of incidence of light, as shown in Figure 2.
1.2 specular reflectance model
Specular reflectance model for material, scholars proposed based on physics specular reflectance model (as BRDF) and based on the specular reflectance model of experience, because Model Calculation complexity based on physics, the realization difficulty is big, and, can obtain than based on the better effect of the model of physics by adjusting the parameter of empirical model.The present invention adopts the experience specular reflectance model, can be expressed as
Figure 986997DEST_PATH_IMAGE027
, in the formula
Figure 459567DEST_PATH_IMAGE010
Be the specularity factor of object,
Figure 494388DEST_PATH_IMAGE028
Be the angle of sight line and reflection direction, as shown in Figure 2.
Figure 357302DEST_PATH_IMAGE029
Be the experience specular reflectance model, described the space distribution of specular light.Parameter
Figure 581610DEST_PATH_IMAGE022
Be material direct reflection index, controlled the smooth degree of minute surface.As shown in Figure 3, when
Figure 597101DEST_PATH_IMAGE022
Big more, curve is steep more, and the expression reflected light concentrates near the reflection direction more, illustrates that the surface is smooth more.
1.3 material light scattering empirical model
The light scattering intensity of material is diffuse reflection component and direct reflection summation.Be expressed as
Figure 819135DEST_PATH_IMAGE030
, the definition integrated reflectance
Figure 418613DEST_PATH_IMAGE013
For when light with
Figure 118716DEST_PATH_IMAGE031
When the angle is incided on certain material surface,
Figure 300298DEST_PATH_IMAGE011
The ratio of the reflective light intensity on the direction and incident intensity, promptly
Figure 443966DEST_PATH_IMAGE032
, this formula is a material light scattering empirical model.Wherein, Be diffuse-reflection factor,
Figure 847582DEST_PATH_IMAGE034
Be specularity factor,
Figure 70622DEST_PATH_IMAGE022
It is the direct reflection index.Material light scattering empirical model has reflected the non-coherent scattering characteristic and the coherent scattering characteristic of material, in order to guarantee the energy conservation requirement This model is than the simple diffuse reflection model that adopts [2]Come the representation space target material to have more rationality.Wherein, diffuse-reflection factor
Figure 21578DEST_PATH_IMAGE033
, specularity factor
Figure 125800DEST_PATH_IMAGE010
, the direct reflection index Relevant with the material self character, promptly on the basis of empirical model, can be with the light scattering characteristic of these three parameter approximate expression materials, with respect to BRDF method based on physical model, under the approaching situation of effect, simplified expression and complexity of calculation, make it more flexible.
2 complex spatial object photon diffusion models
Suppose that the illuminance that the sun produces at the extraterrestrial target place is
Figure 761586DEST_PATH_IMAGE004
, the bin on the incoming cross-section then
Figure 308105DEST_PATH_IMAGE023
(be for extraterrestrial target surface bin
Figure 481597DEST_PATH_IMAGE024
), then the luminous flux of this bin reception is
Figure 679229DEST_PATH_IMAGE036
, when incident light through the cross section is
Figure 647185DEST_PATH_IMAGE023
Corresponding surface
Figure 681000DEST_PATH_IMAGE024
Back reflection, according to the light scattering empirical model of material, its reflection flux is
Figure 127025DEST_PATH_IMAGE037
, the total reflected flux of extraterrestrial target is the integration of incoming cross-section unit's reflected flux on whole cross section, is expressed as , its discrete form is
Figure 22748DEST_PATH_IMAGE039
, when getting the cross section bin
Figure 606176DEST_PATH_IMAGE023
During for constant, order
Figure 42842DEST_PATH_IMAGE040
, following formula can be expressed as , make the cross section average reflectance
Figure 337875DEST_PATH_IMAGE042
, reflection flux then
Figure 346282DEST_PATH_IMAGE043
For,
Figure 88104DEST_PATH_IMAGE044
, this formula is the complex spatial object photon diffusion models based on the cross section integration of derivation, in the formula
Figure 927884DEST_PATH_IMAGE004
For the illumination of the sun, be known quantity at the extraterrestrial target place; Area for effective incoming cross-section;
Figure 638668DEST_PATH_IMAGE018
Be the average reflectance on the cross section.
2.1 effectively incoming cross-section is determined
For the pointolite of infinite distant place, light can be regarded directional light as, and the parallel projection of whole extraterrestrial target on the vertical cross section of incident ray can be regarded the incoming cross-section of extraterrestrial target as.But be not that all light that shine target surface can both reflex in the scope on a certain observed ray.Therefore, be defined in the incoming cross-section can reflection ray be effective incoming cross-section to the part of observed ray.
Work as light source direction
Figure 682716DEST_PATH_IMAGE045
With observed ray
Figure 377003DEST_PATH_IMAGE046
When determining, has only the bin of working as Normal Satisfy with
Figure 95188DEST_PATH_IMAGE048
With
Figure 643981DEST_PATH_IMAGE046
Angle when all spending less than 90, this face could be by irradiate light, and can reflection ray to scope.This Rule of judgment can be expressed as with inner product of vectors , can judge the little bin in extraterrestrial target surface
Figure 936740DEST_PATH_IMAGE024
Corresponding cross section
Figure 57011DEST_PATH_IMAGE023
Whether be effective incoming cross-section.
2.2
Figure 725890DEST_PATH_IMAGE005
Determine elimination with the shade influence
Average reflectance For on the free area each
Figure 411266DEST_PATH_IMAGE023
Corresponding target surface infinitesimal The average of reflectivity.But because target has complicated configuration, an infinitesimal on the incoming cross-section
Figure 619799DEST_PATH_IMAGE023
May be the little bins of a plurality of target surfaces
Figure 721747DEST_PATH_IMAGE024
Projection.And it is different
Figure 963372DEST_PATH_IMAGE024
Since the material difference, reflectivity
Figure 691026DEST_PATH_IMAGE013
Also different, this is
Figure 68917DEST_PATH_IMAGE023
Reflectivity
Figure 607346DEST_PATH_IMAGE013
Determine to have caused difficulty.
Investigating the communication process of light can find, when a light incides the extraterrestrial target surface, the face of first and ray intersection is for being subjected to solarization face on the light ray propagation direction, thereafter face all can be owing to blocking the generation shade, promptly for an incident ray, have only the face nearest just reflected energy to be had contribution, therefore apart from light source
Figure 759104DEST_PATH_IMAGE024
Should get the bin nearest apart from light source.Take this strategy, both determined
Figure 103498DEST_PATH_IMAGE023
Reflectivity
Figure 539158DEST_PATH_IMAGE013
, prevented effectively that again the dash area that is blocked from participating in calculating.
3 models are realized
In order finally to obtain the reflection flux of complex spatial object model at certain direction of observation, key is to try to achieve effective incoming cross-section area of complex spatial object
Figure 45226DEST_PATH_IMAGE050
And average reflectance
Figure 448394DEST_PATH_IMAGE018
But because the extraterrestrial target complex structure, the parsing mathematical model of setting up the extraterrestrial target geometric shape almost is impossible, therefore, utilizes the method for resolving to realize
Figure 330900DEST_PATH_IMAGE050
With
Figure 621067DEST_PATH_IMAGE018
Calculating.Yet, utilize the principle and the method for computer graphics, can try to achieve this two parameters easily.
The ultimate principle that realizes is: at first according to the comprehensive light scattering intensity of material, set up the material photon diffusion models, adopt parallel projection methods to obtain the incoming cross-section of extraterrestrial target, and judge and select effective incoming cross-section, try to achieve average reflectance and effective incoming cross-section area again, set up the complex spatial object photon diffusion models at last.When drawing incoming cross-section, in GPU sheet unit tinter, carry out free area and judge, reject ungratified cross section point.To satisfying the point of free area condition,, in the GPU tinter, realize the calculating of the cross section unit reflectivity empirical model of each pixel representative is formed reflectance map according to the material properties of material.Reflectivity average by pixel on effective incoming cross-section of statistics drafting obtains According to total number of effective incoming cross-section pixel and the area ratio relation of drawing window, obtain effective incoming cross-section area Specific implementation method and step following (is example with OpenGL).
1) how much of extraterrestrial targets and material behavior modeling
Utilize modeling tools such as 3DSMax, can make up the three-dimensional meticulous geometric shape of complex spatial object, and can diffuse reflection and direct reflection parameter be set for each material.In the computer graphics, adopt three components of RGB (RGB) to represent the color of visible light.Three components of RGB are also adopted in the expression of material.Therefore, can diffuse reflection material RGB component be set to (
Figure 110582DEST_PATH_IMAGE033
,
Figure 255256DEST_PATH_IMAGE033
,
Figure 368705DEST_PATH_IMAGE033
), the direct reflection material be set to ( ,
Figure 705194DEST_PATH_IMAGE010
,
Figure 969954DEST_PATH_IMAGE051
), the direct reflection index is set again After, finish the material properties setting of bin.For the surface that has same material on the extraterrestrial target, can be arranged to unified material properties.After each class material set up material properties on the extraterrestrial target, just foundation had how much of the extraterrestrial targets of labyrinth and the three-dimensional model of material behavior.
2) parallel projection conversion
In OpenGL, utilize function
Figure 89668DEST_PATH_IMAGE052
Finish the parallel projection conversion.Function parameter be parallel projection about, up and down with far and near cutting face, utilize these parameters to calculate the real area of view field
Figure 117666DEST_PATH_IMAGE053
,
Figure 236932DEST_PATH_IMAGE015
3) viewport transform
The coordinate transform of the viewport transform after with projective transformation is to the screen pixels coordinate.Utilize function
Figure 879135DEST_PATH_IMAGE054
Realize parameter
Figure 778958DEST_PATH_IMAGE055
Be viewport lower left corner coordinate, Window size (unit is a pixel).Usually get
Figure 318841DEST_PATH_IMAGE057
The sum of all pixels of whole display window is
Figure 627550DEST_PATH_IMAGE058
。
4) 3 D rendering
A) drafting of free area figure
In order to obtain the vertical projection image of extraterrestrial target on the vertical cross section of incident ray, need in OpenGL, be set to the incident light direction by direction of visual lines; Simultaneously, carry out the judgement of free area for making things convenient for GPU, light source direction is set to original detector direction of observation.Utilization is based on the programming technique of GPU, in sheet unit tinter, realize each pixel that will draw of extraterrestrial target three-dimensional model is carried out the judgement of condition (11), and the pixel that satisfies condition is plotted as black, the pixel that does not satisfy condition is depicted as background color (white), finally forms effective incoming cross-section image.
B) drafting of reflectivity distribution plan
The two dimensional image that is made of the reflectivity of each pixel on the effective incoming cross-section of extraterrestrial target is referred to as the reflectivity distribution plan.Obtain the average reflectance distribution plan, need the reflectivity of each pixel on the free area be calculated.In OpenGL, diffuse color and the direct reflection light color of light source all are set to (1.0,1.0,1.0), and direction of visual lines is set to the incident light direction; Enable depth test, guarantee correct hiding relation, to eliminate the influence of shade.In extraterrestrial target three-dimensional model drawing process, be each leg-of-mutton material assignment with diffuse reflection and direct reflection parameter in the model data, in OpenGL sheet unit tinter,, utilize formula according to light source attribute, material properties and geometric relationship
Figure 749090DEST_PATH_IMAGE032
(4), finish calculating to each pixel reflectivity on the incoming cross-section.After modeling rendering finishes, just constituted the reflectivity distribution plan of whole extraterrestrial target.
C) parameter
Figure 56575DEST_PATH_IMAGE059
With
Figure 212749DEST_PATH_IMAGE018
Determine
Through behind the above-mentioned several steps, on two-dimentional window, obtain the effective incoming cross-section figure and the reflectance map of extraterrestrial target.Because what the acquisition process of free area adopted is parallel projection, the area of each pixel representative is identical on the window.Therefore, by detecting valid pixel (black picture element) on effective incoming cross-section figure, and add up and obtain valid pixel and add up to ,
Figure 805591DEST_PATH_IMAGE019
Multiply by the real area of each pixel representative, just obtain effective incoming cross-section area of complex spatial object, be expressed as , with the reflectivity summation of each pixel on the reflectivity distribution plan, and divided by
Figure 661868DEST_PATH_IMAGE019
, just can obtain average reflectance
Figure 318240DEST_PATH_IMAGE018
4 l-G simulation tests
4.1 test figure
For the validity and the actual effect of the method for verifying the calculation of complex extraterrestrial target light scattering characteristic that this paper proposes, be extraterrestrial target with the Quickbird-2 satellite, be that observation satellite is tested orbital tracking such as table 1 with certain analog satellite Sat-1.QuickBird-2 is an earth observation satellite, and attitude is for pointing to over the ground, and its geometry is comparatively complicated, and profile as shown in Figure 4.
 
Figure 414372DEST_PATH_IMAGE061
Calculate by track, drawing the initial moment is 2008-1-11 00:52:05(UTC), be 2008-1-11 01:50:36(UTC the finish time) in totally 3511 second time period, Sat-1 can implement observation to the Qiuckbird-2 satellite.Fig. 5 is in the test period section, and target is to the distance of observation platform and the time dependent situation of angle of solar direction and observed ray.As can be seen from the figure, the angle of solar direction and observed ray exists
Figure 63659DEST_PATH_IMAGE062
Have bigger span in the interval, utilize the illumination condition in this time period to test, have more general representativeness.
4.2 test findings
Utilize the principle and the method for the calculation of complex extraterrestrial target light scattering that the present invention proposes, with 10 seconds was step-length, obtain each constantly effective incoming cross-section figure and reflectivity distribution plan, and added up effective cross-sectional area and average reflectance, finally calculated reflection flux.The result is as follows:
Fig. 6 is is 2008-1-11 01:08:25(the time apart from zero-time 1000 seconds) total incoming cross-section figure (a) and the effectively comparison of incoming cross-section figure (b).Fig. 7 is effectively incoming cross-section and total time dependent comparison curves of incoming cross-section area in the section between at the trial.
Effectively the geometric configuration and the attitude of incoming cross-section and satellite are all closely related.In addition, analysis chart 6 and Fig. 7, as can be seen, effectively incoming cross-section obviously is subjected to the influence of solar direction and observed ray angle, and the total trend of effective incoming cross-section is opposite with the variation of solar direction and observed ray corner dimension; When angle was spent near 180, effectively incoming cross-section was tending towards 0; And angle hour, and free area surpasses 12 square metres, and span scope is bigger.This Changing Pattern and actual conditions match.In addition,, find that effectively incoming cross-section is little more many than total incoming cross-section usually, differ about 3 times constantly as Fig. 6 by more effective incoming cross-section and total incoming cross-section.Therefore, do not carry out the judgement of effective incoming cross-section, and directly adopt total incoming cross-section bring great error can for the calculating of reflected energy.
The 2008-1-11 01:08:25 reflectivity distribution plan constantly that Fig. 8 draws for test, color is deeply felt more and is shown that reflectivity is low more.As can be seen from the figure because direction of visual lines is arranged on light source direction, the irradiation of extraterrestrial target glazed thread less than dash area by the OpenGL depth test, hidden automatically, can not participate in the calculating of average reflectance.The method based on effective incoming cross-section integration is adopted in this explanation, can prevent that shade from producing interference.
Fig. 9 is the time dependent curve of target average reflectivity.As can be seen from Figure 9, near 3000 seconds, average reflectance has violent shake, is because in this time period, solar direction and observed ray angle cause effective incoming cross-section near 0 near 180 degree, have amplified the measurement stochastic error.On the other hand, when solar direction and observed ray are spent near 180, be subjected to the influence of strong sunray direct projection, general device all can't be observed.Therefore, the data that obtain in this zone are invalid data, it should be ignored.Like this, the average reflectance of this extraterrestrial target changes between 0.1～0.25 greatly in observed ray.This phenomenon explanation, along with the variation of incident angle and view angle, certain variation also can take place in average reflectance.
Get the illumination of the sun at the extraterrestrial target place
Figure 194426DEST_PATH_IMAGE063
Be solar constant 1353
Figure 520234DEST_PATH_IMAGE064
, with free area and average reflectance substitution formula
Figure 775766DEST_PATH_IMAGE044
, calculate the reflection flux of each step-length.Change curve is as shown in figure 10 in time for it.
By formula
Figure 291061DEST_PATH_IMAGE003
As can be known, incoming cross-section And average reflectance Contribution for reflection flux is identical.But comparison diagram 7, Fig. 9 find that effectively incoming cross-section has mainly influenced the total variation tendency of reflection flux.This is because in the observation time section, effectively incoming cross-section is long-pending
Figure 17337DEST_PATH_IMAGE067
Variation than average reflectance Much violent.And effectively incoming cross-section is had the greatest impact by illumination condition.
For the research of the light scattering characteristic of extraterrestrial target, Most scholars all is used as target the simple geometric body.And the present invention is on the basis of the light scattering experimental formula that non-coherent scattering characteristic and coherent scattering characteristic according to material draw, set up the photon diffusion models that complex spatial object utilizes sectional area and average reflectance to represent on effective incoming cross-section, and provided the method that accurately obtains effective incoming cross-section and average reflectance based on computer graphics.At last, calculated at one section may observe Quickbird-2 satellite space-based is observed in the time effective incoming cross-section, average reflectance and reflection flux etc.

Claims (9)

1. a light scattering modeling method for complex spatial object is characterized in that, the step of this method is as follows:
(1) according to the comprehensive light scattering intensity of material, sets up material light scattering empirical model;
(2) adopt the parallel projection conversion to obtain the incoming cross-section of extraterrestrial target, and judge and select effective incoming cross-section;
(3) according to material light scattering empirical model, the reflectivity average of pixel obtains average reflectance on effective incoming cross-section that statistics is drawn
Figure 764900DEST_PATH_IMAGE002
(4) according to effective total number of incoming cross-section pixel and the area ratio relation of drawing window, try to achieve effective incoming cross-section area
Figure 769765DEST_PATH_IMAGE004
(5) set up the complex spatial object photon diffusion models
Figure 207700DEST_PATH_IMAGE006
, in the formula
Figure 893896DEST_PATH_IMAGE008
Be the illumination of the sun at the extraterrestrial target place;
Figure 664668DEST_PATH_IMAGE004
Area for effective incoming cross-section;
Figure DEST_PATH_IMAGE009
Be the average reflectance on the cross section.
2. light scattering modeling method for complex spatial object according to claim 1 is characterized in that, the comprehensive light scattering intensity of material is diffuse reflection component and direct reflection summation in the described step (1), is expressed as , wherein
Figure 765665DEST_PATH_IMAGE013
Be the diffuse-reflection factor of object, relevant with body surface character;
Figure 989973DEST_PATH_IMAGE015
It is the light intensity of light source;
Figure 317049DEST_PATH_IMAGE017
Be angle of incidence of light;
Figure 398138DEST_PATH_IMAGE019
Be the specularity factor of object,
Figure 810664DEST_PATH_IMAGE021
Angle for sight line and reflection direction.
3. light scattering modeling method for complex spatial object according to claim 2 is characterized in that: material light scattering empirical model is in the described step (1)
Figure 838663DEST_PATH_IMAGE023
, wherein
Figure 82563DEST_PATH_IMAGE025
Be integrated reflectance, be when light with When the angle is incided on certain material surface,
Figure 172059DEST_PATH_IMAGE021
The ratio of the reflective light intensity on the direction and incident intensity.
4. light scattering modeling method for complex spatial object according to claim 3, it is characterized in that: the acquisition of space target incoming cross-section is in OpenGL in the described step (2), utilize function glOrtho (l, r, b, t, n, f) finish the parallel projection conversion, function parameter be parallel projection about, up and down with far and near cutting face, with the real area of these calculation of parameter view fields
Figure DEST_PATH_IMAGE027
, (w h) transforms to the screen pixels coordinate with the left side after the projective transformation for x, y, and (x y) is viewport lower left corner coordinate to parameter, and (w h) is window size, gets x=y=0, and then the sum of all pixels of whole display window is to use function glViewport again
Figure DEST_PATH_IMAGE029
5. light scattering modeling method for complex spatial object according to claim 4 is characterized in that: described step (2), and when drawing incoming cross-section, in GPU sheet unit tinter, carry out free area and judge, reject the cross section point that does not satisfy Rule of judgment; To satisfying the point of free area condition, according to the material properties of material, the cross section unit reflectivity empirical model to each pixel representative in the GPU tinter calculates, and forms the reflectivity distribution plan.
6. light scattering modeling method for complex spatial object according to claim 5, it is characterized in that: described free area is the part that the energy reflection ray arrives observed ray in incoming cross-section, when light source direction L and observed ray V determine, when the angle of being satisfied with L and V when the normal N of bin dA is all spent less than 90, this face is by irradiate light, and the energy reflection ray is to scope, and the Rule of judgment of this free area is expressed as with inner product of vectors:
Figure DEST_PATH_IMAGE031
7. light scattering modeling method for complex spatial object according to claim 6, it is characterized in that: the two dimensional image that described reflectivity distribution plan is made of the reflectivity of each pixel on the effective incoming cross-section of extraterrestrial target, with diffuse reflection in the model data and direct reflection parameter is each leg-of-mutton material assignment, in OpenGL sheet unit tinter,, utilize formula according to light source attribute, material properties and geometric relationship
Figure 361338DEST_PATH_IMAGE023
, finish calculating to each pixel reflectivity on the incoming cross-section, after modeling rendering finishes, just constituted the reflectivity distribution plan of whole extraterrestrial target.
8. light scattering modeling method for complex spatial object according to claim 7 is characterized in that: average reflectance in the described step (3)
Figure 663006DEST_PATH_IMAGE002
Be reflectivity summation with each pixel on the reflectivity distribution plan, and divided by the valid pixel sum
Figure DEST_PATH_IMAGE033
Obtain.
9. light scattering modeling method for complex spatial object according to claim 8 is characterized in that, effective incoming cross-section area in the described step (4)
Figure DEST_PATH_IMAGE034
Computing formula as follows:
Figure DEST_PATH_IMAGE036
, wherein valid pixel adds up to
Figure 413794DEST_PATH_IMAGE033
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