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tutorials:basic-spectral-light-modeling

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tutorials:basic-spectral-light-modeling [2024/12/05 09:14] – added the example part MHtutorials:basic-spectral-light-modeling [2025/01/08 21:30] (current) – MH
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 ====== Spectral Light Modelling ====== ====== Spectral Light Modelling ======
- 
-===== General Introduction ===== 
- 
-Light modelling generally involves three aspects: 
- 
-  * Global illumination model 
-  * Light sources 
-  * Local illumination model 
- 
-{{ :tutorials:light1.png?direct&400 |}} 
- 
-Whereas the Global illumination model handles the actual light computation, the Light sources are the light-emitting elements, and the Local illumination model defines the optical properties of the scene objects. 
- 
-In each aspect, computer graphics offers plenty of alternatives. 
- 
-{{ :tutorials:light2.png?direct&400 |}} 
- 
-Several of them are implemented in GroIMP as ready-to-use tools. 
- 
-GroIMP integrates two two main **light model implementations**, namely: 
- 
-  * Twilight, a CPU-based implementation  
-  * GPUFlux, a GPU-based implementation 
- 
-Both implementing different global illumination model for rendering and for light computation. 
- 
-{{ :tutorials:light3.png?direct&400 |}} 
- 
-In the following, only light computation or light modelling will be discussed. 
- 
- 
-Regarding light sources, GroIMP provides a complete set of possible implementations. They all implement the //Light// and //LightBase// interfaces, which makes them easy to handle and exchange. 
- 
-{{ :tutorials:light4.png?direct&200 |}} 
- 
-For the Local illumination model, which defines the optical properties of the scene objects such as values for absorption, transmission, and reflection, so-called shaders are used. 
- 
-{{ :tutorials:light5.png?direct&200 |}} 
- 
-GroIMP provides a set of standard shader implementations, e.g., for Lambert and Phong shading. Whereas the Lambertian model supports only diffuse reflection, the Phong reflection model (B.T. Phong, 1973) combines ambient, diffuse, and specular light reflections. 
- 
-{{ :tutorials:light6.png?direct&400 |}} 
- 
- 
-===== Spectral light modelling ===== 
- 
  
 These three core aspects of light simulation—global and local illumination models, and light sources—are the base for any light simulation. When it comes to spectral light simulations, specialized implementations of the aforementioned aspects are required, capable of simulating not only one or three light channels, as is typical for common light models, but also the entire light spectrum for different wavelengths. These three core aspects of light simulation—global and local illumination models, and light sources—are the base for any light simulation. When it comes to spectral light simulations, specialized implementations of the aforementioned aspects are required, capable of simulating not only one or three light channels, as is typical for common light models, but also the entire light spectrum for different wavelengths.
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 // disables the simulation of sensor // disables the simulation of sensor
-LM.setEnableSensors(false); // default: true+LM.setEnableSensors(true); // default: false
  
 // sets the random seed for the random number generator; us this to obtain reproducible results // sets the random seed for the random number generator; us this to obtain reproducible results
 LM.setRandomseed(123456); LM.setRandomseed(123456);
  
-// disables dispersion +// enable dispersion 
-LM.setDispersion(false); // default: true+LM.setDispersion(ture); // default: false
 </code> </code>
  
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 Phong myShader = new Phong(); Phong myShader = new Phong();
 myShader.setDiffuse(GREEN_SPD); myShader.setDiffuse(GREEN_SPD);
-myShader.setTrasnparency(RED_SPD);+myShader.setTransparency(RED_SPD);
  
  
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         myShader.setDiffuse(GREEN_SPD);         myShader.setDiffuse(GREEN_SPD);
         myShader.setTransparency(RED_SPD);         myShader.setTransparency(RED_SPD);
-        myShader.setSpecularCONST_SPD);+        myShader.setSpecular(CONST_SPD);
                  
         //set the shader to the TestBox         //set the shader to the TestBox
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 } Box(0.001,1,1).(setShader(myShader)); } Box(0.001,1,1).(setShader(myShader));
 </code> </code>
 +
 +Within the //CIENormSpectralCurve// class, a small database of several predefined standard spectral curves is given:
 +
 +  * on 1nm resolution [300, 780]
 +    * A, D65
 +  * on 5nm resolution [300, 780]
 +    * A, C, D50, D55, D65, D75
 +  * on 5nm resolution [380, 780]
 +    * FL1-12, FL3_1-15, HP1-5
 +
 +For instance, to use the predefined CIE NORM D65 for typical sun light within a user defined light module, one could use the following code.
 +
 +<code java>
 +import de.grogra.imp3d.objects.Attributes;
 +import de.grogra.gpuflux.imp3d.spectral.CIENormSpectralCurve; 
 +
 +//define a light module
 +module MyLamp extends LightNode {
 +  {
 +    setLight(
 +      new SpectralLight(
 +        new CIENormSpectralCurve(Attributes.CIE_NORM_D65)
 +      ).(
 + setPower(100), //[W]
 + setLight(
 +   new SpotLight(DISTRIBUTION).(
 +     setVisualize(true), //activate light ray visualization
 +            setNumberofrays(250), 
 +            setRaylength(1)// [m]
 +          )
 +        )
 +      ) //end SpectralLight
 +    ); //end setLight
 +  }
 +}
 +</code>
 +
 +
 +
 +Note: Do NOT mix common RGB shader like the //RGBAShader// with spectral shader! This applies for having RGB and spectral shader within the same model but in different objects but also for one (Phong) shader thas combines RGB and spectral shader. The ranges of common RGB shader will most probably not match the ranges of the other shader and simulated light spectrum what will inevitable lead to fals results.
  
  
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 To monitor light distributions with a scene without interfering, GroIMP provides the //SensorNode// class, a sphere that can be placed arbitrarily within the scene. To obtain the sensed spectrum, the //getSensedIrradianceMeasurement// function needs to be called. To monitor light distributions with a scene without interfering, GroIMP provides the //SensorNode// class, a sphere that can be placed arbitrarily within the scene. To obtain the sensed spectrum, the //getSensedIrradianceMeasurement// function needs to be called.
  
-Note: the size of the sensor node directly correlates with the probability of got hit by a light ray. For a very small sphere the probability to got hit by a light ray is relatively low, so the number of light rays simulated by the light model needs to be much larger to get repayable results. Therefore, better not to use very small sensor nodes.+Note: The size of the sensor node directly correlates with the probability of got hit by a light ray. For a very small sphere the probability to got hit by a light ray is relatively low, so the number of light rays simulated by the light model needs to be much larger to get repayable results. Therefore, better not to use very small sensor nodes.
  
-Note: the colour of the sensor node determines which wavelengths should be observed. The default value is white, what stands for monitor all colours. If, for instance, the sensor colour is set to red, only red spectra will be sensed.+Note: The colour of the sensor node determines which wavelengths should be observed. The default value is white, what stands for monitor all colours. If, for instance, the sensor colour is set to red, only red spectra will be sensed.
  
-Note: the output of a sensor node is normalized to absorbed radiance per square meter, independent of the actual size of the sensor. +Note: The output of a sensor node is normalized to absorbed radiance per square meter, independent of the actual size of the sensor. 
  
 Note: Sensor nodes can be enabled and disabled for the light model using the LM.setEnableSensors(true/false) function. By default they are disabled, since GroIMP version 2.1.4, before they were enabled by default. Having them disabled speeds up the light computation time for scenarios where not sensor nodes are involved.  Note: Sensor nodes can be enabled and disabled for the light model using the LM.setEnableSensors(true/false) function. By default they are disabled, since GroIMP version 2.1.4, before they were enabled by default. Having them disabled speeds up the light computation time for scenarios where not sensor nodes are involved. 
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 In the following four minimal working examples are given to illustrate: the light model, the definition of light sources, adding a object and define a spectral shader, and on how to visualize the results. The four examples are building on each other, meaning with each example new parts will extend the previous code. In the following four minimal working examples are given to illustrate: the light model, the definition of light sources, adding a object and define a spectral shader, and on how to visualize the results. The four examples are building on each other, meaning with each example new parts will extend the previous code.
  
-Note: The examples require GroIPM version >=2.0 to run. With GroIMP version 2.0 some changes on the internal package structure are made. formally classes found in  de.grogra.imp3d have been moved to de.grogra.gpuflux.imp3d to match the package name (Java 11 forbid package name split). So, if you are using objects, lights or shaders from gpuflux, they should be imported as de.grogra.gpuflux.imp3d.xxx.+Note: The examples require GroIMP version >=2.0 to run. With GroIMP version 2.0 some changes on the internal package structure are made. formally classes found in  //de.grogra.imp3d// have been moved to //de.grogra.gpuflux.imp3d// to match the package name (Java 11 forbid package name split). So, if you are using objects, lights or shaders from //gpuflux//, they should be imported as //de.grogra.gpuflux.imp3d.xxx//.
  
 <code java> <code java>
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 === Example 1 - Light Model === === Example 1 - Light Model ===
-This example just defines the GUPFlux light model and parameterizes it to simulate a spectrum from 300 to 800nm and measure the results in 30 buckets.+This example just defines the GPUFlux light model and parameterizes it to simulate a spectrum from 300 to 800nm and measure the results in 30 buckets.
  
 <code java> <code java>
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  println("Run GPU light model", 0x000000);  println("Run GPU light model", 0x000000);
  FluxLightModel GPU_LM = new FluxLightModel(RAYS, DEPTH);  FluxLightModel GPU_LM = new FluxLightModel(RAYS, DEPTH);
- GPU_LM.setSeed(12345); // to produce reproduceable results+ GPU_LM.setSeed(12345); // to produce reproducible results
  GPU_LM.setMeasureMode(MeasureMode.FULL_SPECTRUM);  GPU_LM.setMeasureMode(MeasureMode.FULL_SPECTRUM);
  GPU_LM.setSpectralDomain(300,800);// spectral range monitored  GPU_LM.setSpectralDomain(300,800);// spectral range monitored
tutorials/basic-spectral-light-modeling.1733386491.txt.gz · Last modified: 2024/12/05 09:14 by MH