GroIMP wiki

a part of grogra.de

User Tools

Site Tools

Trace:
tutorials:basic-spectral-light-modeling

Differences

This shows you the differences between two versions of the page.

Link to this comparison view

Both sides previous revisionPrevious revision
Next revision		Previous revision
tutorials:basic-spectral-light-modeling [2025/06/02 21:24] – [Local illumination - Shader] MHtutorials:basic-spectral-light-modeling [2025/06/04 14:08] (current) – MH
Line 7: Line 7:
 {{ :tutorials:light_preferences.png?direct&400 |}} {{ :tutorials:light_preferences.png?direct&400 |}}
  
-Spectral light simulations now deal not only with the pure calculation of light distributions but also include aspects of the principal characteristics of light, i.e., light quality, quantity, and duration.+Spectral light simulations now deal not only with the pure calculation of light distributions it's intensity (or quantity), and duration, but further includes the aspect of light quality.
  
 {{ :tutorials:light7.png?direct&400 |}} {{ :tutorials:light7.png?direct&400 |}}
Line 49: Line 49:
     LM.setSpectralBuckets(21); // get 20 buckets; set to N+1 to get N     LM.setSpectralBuckets(21); // get 20 buckets; set to N+1 to get N
     LM.setSpectralDomain(380, 720); // minimum and maximum lambda, default settings     LM.setSpectralDomain(380, 720); // minimum and maximum lambda, default settings
 +...    
 } }
 </code> </code>
Line 82: Line 83:
 </code> </code>
  
-To obtain the total amount of absorbed radiation of a node x, the //getAbsorbedPowerMeasurement()// function of the light model needs to be called. The returned measurement object contains the results for the specific object x. By calling the //integrate()// function, the integral, or simply sum, will be calculated. +To obtain the total amount of absorbed radiation of a node x, the //getAbsorbedPowerMeasurement()// function of the light model needs to be called. (Note: For the GPUFlux light model one needs to call //getAbsorbedPowerMeasurement()// and not //getAbsorbedPower()// as for the Twilight light model. And the return value is a //Measurement// and not a //Spectrum//) The returned measurement object contains the results for the specific object x. By calling the //integrate()// function, the integral, or simply sum, will be calculated.
  
 <code java> <code java>
 +import de.grogra.gpuflux.scene.experiment.Measurement;
 +
 Measurement spectrum = LM.getAbsorbedPowerMeasurement(x); Measurement spectrum = LM.getAbsorbedPowerMeasurement(x);
 float absorbedPower = spectrum.integrate(); float absorbedPower = spectrum.integrate();
 </code> </code>
 +
 +Have in mind, the unit here is Watt. The output power of the light sources is set in Watt and the values for absorption, reflectance, transmission are in Watt too.
  
 By doing this within a rule, the light absorption can be obtained for all objects of the specified type, such as a //Box//, as in this example: By doing this within a rule, the light absorption can be obtained for all objects of the specified type, such as a //Box//, as in this example:
Line 134: Line 139:
  
 <code java> <code java>
 +import de.grogra.gpuflux.imp3d.spectral.SpectralCurve;
 +import de.grogra.gpuflux.imp3d.spectral.IrregularSpectralCurve;
 +
 const float[] WAVELENGTHS = {380, 410, 420, 450, 465, 480, 490, 600, 620, 630, 640, 655, 660, 670, 690, 700, 720}; const float[] WAVELENGTHS = {380, 410, 420, 450, 465, 480, 490, 600, 620, 630, 640, 655, 660, 670, 690, 700, 720};
-const AMPLITUDES = {0.05, 0.1, 0.4, 0.63, 0.25, 0.15, 0.05, 0.01, 0.1, 0.3, 0.4, 0.85, 0.75, 0.95, 0.6, 0.25, 0.1};+const float[] AMPLITUDES = {0.05, 0.1, 0.4, 0.63, 0.25, 0.15, 0.05, 0.01, 0.1, 0.3, 0.4, 0.85, 0.75, 0.95, 0.6, 0.25, 0.1};
  
-const ChannelSPD TEST_SPD = new ChannelSPD(new IrregularSpectralCurve(WAVELENGTHS, AMPLITUDES)); +const SpectralCurve TEST_SPD = new IrregularSpectralCurve(WAVELENGTHS, AMPLITUDES)); 
 </code> </code>
 +
 +**SPD** = **S**pectral **P**ower **D**istribution
 +
  
 Besides user-defined spectral curves, GroIMP provides a set of spectral curves:  Besides user-defined spectral curves, GroIMP provides a set of spectral curves:
Line 149: Line 160:
  
 {{ :tutorials:light_SpectralCurve.png?direct&200 |}} {{ :tutorials:light_SpectralCurve.png?direct&200 |}}
- 
  
 Since these spectral curve classes all implement the same //SpectralCurve// interface, they can be used in the same way and are therefore exchangeable.  Since these spectral curve classes all implement the same //SpectralCurve// interface, they can be used in the same way and are therefore exchangeable.
  
 <code java> <code java>
 +import de.grogra.gpuflux.imp3d.spectral.SpectralCurve;
 +import de.grogra.gpuflux.imp3d.spectral.IrregularSpectralCurve;
 +import de.grogra.gpuflux.imp3d.shading.ChannelSPD; 
 +
 //user defined spectral curve, applied to an IrregularSpectralCurve //user defined spectral curve, applied to an IrregularSpectralCurve
 float[] WAVELENGTHS = {380, 485, 490, 610, 615, 720}; float[] WAVELENGTHS = {380, 485, 490, 610, 615, 720};
Line 171: Line 185:
 ChannelSPD REG_SPD = new ChannelSPD(new CIENormSpectralCurve(Attributes.CIE_NORM_D55)); ChannelSPD REG_SPD = new ChannelSPD(new CIENormSpectralCurve(Attributes.CIE_NORM_D55));
  
-// a black body spectral curve with a temperature of 5000K+//a black body spectral curve with a temperature of 5000K
 ChannelSPD REG_SPD = new ChannelSPD(new BlackbodySpectralCurve(5000)); ChannelSPD REG_SPD = new ChannelSPD(new BlackbodySpectralCurve(5000));
 </code> </code>
Line 177: Line 191:
 {{ :tutorials:light11.png?direct&600 |}} {{ :tutorials:light11.png?direct&600 |}}
  
-To use the spectral curve as input for a light source, a //SpectralLight// needs to be defined. +To use the spectral curve as input for a light source, a //SpectralLight// needs to be defined. In the example below, a //SpectralLight// is defined as //PointLight// that emitts a user-defined //IrregularSpectralCurve//.
  
 <code java> <code java>
-const float[] WAVELENGTHS = {380,385,...}; +import de.grogra.gpuflux.imp3d.objects.SpectralLight; 
-const float[] AMPLITUDES = {0.000967721, 0.000980455, ...};+import de.grogra.gpuflux.imp3d.spectral.SpectralCurve; 
 +import de.grogra.gpuflux.imp3d.spectral.IrregularSpectralCurve; 
 +  
 +//user defined spectral curve, applied to an IrregularSpectralCurve 
 +const float[] WAVELENGTHS = {380, 485, 490, 610, 615, 720}; 
 +const float[] AMPLITUDES = {0,0,1,1,0,0}; 
 +const SpectralCurve TEST_SPD = new IrregularSpectralCurve(WAVELENGTHS, AMPLITUDES);  
  
 module MyLamp extends LightNode() { module MyLamp extends LightNode() {
     {     {
         setLight(         setLight(
-            new SpectralLight(new IrregularSpectralCurve(WAVELENGTHS, AMPLITUDES)).(+            new SpectralLight(TEST_SPD).(
                 setPower(100), // [W]                 setPower(100), // [W]
                 setLight(new PointLight())                 setLight(new PointLight())
Line 193: Line 214:
     }     }
 } }
 +
 +protected void init() [
 + Axiom ==> MyLamp;
 +]
 </code> </code>
  
 +Note: //ChannelSPD// are the input for shader, while //SpectralCurve// is the expected input data type for //LightNodes// objects.
 +
 +Within the //CIENormSpectralCurve// class, a small database of several predefined standard spectral curves is given:
 +
 +  * at 1nm resolution [300, 780]
 +    * A, D65
 +  * at 5nm resolution [300, 780]
 +    * A, C, D50, D55, D65, D75
 +  * at 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.gpuflux.imp3d.spectral.CIENormSpectralCurve; 
 +import de.grogra.gpuflux.imp3d.objects.SpectralLight;
 +
 +//define a light module
 +module MyLamp extends LightNode {
 +  {
 +    setLight(
 +      new SpectralLight( new CIENormSpectralCurve(Attributes.CIE_NORM_D65) ).(
 + setPower(100), //[W]
 + setLight(new PointLight())
 +      ) //end SpectralLight
 +    ); //end setLight
 +  }
 +}
 +</code>
 +
 +
 +Using the SPD, we define the light 'composition' or light quality.
 +
 +In the above example, a //PointLight// is used as light source to emit the wanted spectrum. In the next step, we will continue and show how to define and use user-defined light emission pattern. The keyword here is **PLD** = **P**hysical **L**ight **D**istribution.
  
-To complete the definition of a light source, besides the spectral power distribution, the physical light distribution (PLD), which defines the light pattern, needs to be defined. This is especially helpful or necessary for any definition of artificial light sources, such as those found in greenhouses, including HPS lamps or modern LED-based light systems, which are usually equiped with a reflector.+This is especially helpful or necessary for any definition of artificial light sources, such as those found in greenhouses, including HPS lamps or modern LED-based light systems, which are usually equiped with a reflector.
  
 The physical light distribution can be defined as a polar distribution diagram (also called polar curve) showing the luminous intensity values with increasing angles from two imaginary axes of the lamp, which is placed in the centre. Red: 0–180◦ plane, blue 90–270◦ plane. On the right of the figure below, a 3D visualisation of the same light source is given. The colour of each point (gradient from black to bright red), as well as the distance to the light source, both indicate the power emitted by the light source in a particular direction per unit solid angle. The physical light distribution can be defined as a polar distribution diagram (also called polar curve) showing the luminous intensity values with increasing angles from two imaginary axes of the lamp, which is placed in the centre. Red: 0–180◦ plane, blue 90–270◦ plane. On the right of the figure below, a 3D visualisation of the same light source is given. The colour of each point (gradient from black to bright red), as well as the distance to the light source, both indicate the power emitted by the light source in a particular direction per unit solid angle.
Line 222: Line 281:
 {{ :tutorials:light_visulizedLightSources.png?direct&500 |}} {{ :tutorials:light_visulizedLightSources.png?direct&500 |}}
  
-To see a more realistic light pattern, the scene needs to be rendered using one of the light models. Below is a rendered image of the LampDemo.gsz, as it can be found in the GroIMP internal example gallery. +To see a more realistic light pattern, the scene needs to be rendered using one of the light models. Below is a rendered image of the //LampDemo.gsz//, as it can be found in the GroIMP internal example gallery.
  
 {{ :tutorials:light_lampDemo.png?direct&500 |}} {{ :tutorials:light_lampDemo.png?direct&500 |}}
Line 229: Line 288:
 Defining a PLD for a light source can be done in two ways: 1) 'manually' by defining the polar curve as an array of intensities within XL, or 2) by importing a PLD file—as it is provided by most professional light companies for their products. Defining a PLD for a light source can be done in two ways: 1) 'manually' by defining the polar curve as an array of intensities within XL, or 2) by importing a PLD file—as it is provided by most professional light companies for their products.
  
-In any case, instead of one of the predefined light sources, such as //PointLight//, //SpotLight//, or //DirectionalLight//, a so-called //PhysicalLight// needs to be defined. The //PhysicalLight// allows us to apply a PLD to it. For the 'manual way,' the PLD is defined as a two-dimensional array (called DISTRIBUTION in the code snippet below) that is then passed as an input parameter to the //PhysicalLight// class.+In any case, instead of one of the predefined light sources, such as //PointLight//, //SpotLight//, or //DirectionalLight//, a so-called **//PhysicalLight//** needs to be defined. The //PhysicalLight// allows us to apply a PLD to it. For the 'manual way,' the PLD is defined as a two-dimensional array (called DISTRIBUTION in the code snippet below) that is then passed as an input parameter to the //PhysicalLight// class.
  
  
Line 254: Line 313:
 } }
 </code> </code>
 +
 +
 +A PLD distribution is defined as two-dimensional array, where the values of each row represent the intensities in one direction, starting at 90 degree (above the light source) going down to 270 degree (right below the light source), covering 180 degree. The values given are equally distributed of the 180 degree, e.g., when only three values are given, the first will be associated with 90 degree, the second with zero and the third with 270 degree. The rows on the other hand are equally distributed around the virtual z-axis, around the light source. If only one row is given, this distribution defined within the first row, will be used equally around the whole light source. If two rows are given, the first one will be used at zero degree and the second one at 180 degree. The values in-between are interpolated. The intensities are given in ether in absolute values (in Watt) or in percent in the range or zero to one or zero to 100. They are normalized internally again.
  
  
Line 269: Line 331:
  
 <code java> <code java>
-float[] WAVELENGTHS = {380, 485, 490, 610, 615, 720}; +import de.grogra.gpuflux.imp3d.shading.ChannelSPD; 
-float[] AMPLITUDES = {0,0,1,1,0,0}; +import de.grogra.gpuflux.imp3d.spectral.IrregularSpectralCurve; 
-ChannelSPD GREEN_SPD = new ChannelSPD(new IrregularSpectralCurve(WAVELENGTHS, AMPLITUDES)); +import de.grogra.gpuflux.imp3d.spectral.RGBSpectralCurve; 
 +import de.grogra.gpuflux.imp3d.spectral.ConstantSpectralCurve;
  
-ChannelSPD RED_SPD = new ChannelSPD(new RGBSpectralCurve(0.8,0,0));  +static float[] WAVELENGTHS = {380, 485, 490, 610, 615, 720}; 
-ChannelSPD CONST_SPD = new ChannelSPD(new ConstantSpectralCurve(0.25)); +static float[] AMPLITUDES = {0,0,1,1,0,0}; 
 +static ChannelSPD GREEN_SPD = new ChannelSPD(new IrregularSpectralCurve(WAVELENGTHS, AMPLITUDES)); 
  
-Phong myShader = new Phong(); +static ChannelSPD RED_SPD = new ChannelSPD(new RGBSpectralCurve(0.8,0,0));  
-myShader.setDiffuse(GREEN_SPD); +static ChannelSPD CONST_SPD = new ChannelSPD(new ConstantSpectralCurve(0.25)); 
-myShader.setTransparency(RED_SPD);+
  
 +//shader definition as global variable
 +Phong myShader0 = new Phong();
 +static {
 +  myShader0.setDiffuse(GREEN_SPD);
 +  myShader0.setTransparency(RED_SPD);
 +}
  
-//within a module that extends a Box+//and use of the global shader within a module that is interpreted as Box 
 +module TestBox ==> { 
 +} Box(0.001,1,1).(setShader(myShader0)); 
 + 
 + 
 +//or define the shader within a module that extends a Box
 module TestBox extends Box(0.001,1,1) { module TestBox extends Box(0.001,1,1) {
          
Line 299: Line 373:
     }     }
 } }
- 
-//as a module that is interpreted as Box 
-module TestBox ==> { 
-    Phong myShader = new Phong(); 
-} Box(0.001,1,1).(setShader(myShader)); 
 </code> </code>
- 
-Within the //CIENormSpectralCurve// class, a small database of several predefined standard spectral curves is given: 
- 
-  * at 1nm resolution [300, 780] 
-    * A, D65 
-  * at 5nm resolution [300, 780] 
-    * A, C, D50, D55, D65, D75 
-  * at 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.gpuflux.imp3d.spectral.CIENormSpectralCurve;  
-import de.grogra.gpuflux.imp3d.objects.PhysicalLight; 
- 
-//define a light module 
-module MyLamp extends LightNode { 
-  { 
-    setLight( 
-      new SpectralLight( 
-        new CIENormSpectralCurve(Attributes.CIE_NORM_D65) 
-      ).( 
- setPower(100), //[W] 
- setLight( 
-   new PhysicalLight(DISTRIBUTION).( 
-     setVisualize(true), //activate light ray visualization 
-            setNumberofrays(250),  
-            setRaylength(1)// [m] 
-          ) 
-        ) 
-      ) //end SpectralLight 
-    ); //end setLight 
-  } 
-} 
-</code> 
- 
- 
  
 Note: Do NOT mix common RGB shaders (like the //RGBAShader//) and spectral shaders! This applies to having RGB and spectral shaders within the same model but in different objects but also for one (Phong) shader that combines RGB and spectral shaders. The ranges of common RGB shaders will most probably not match the ranges of the other shader and the simulated light spectrum which will inevitably lead to false results. Note: Do NOT mix common RGB shaders (like the //RGBAShader//) and spectral shaders! This applies to having RGB and spectral shaders within the same model but in different objects but also for one (Phong) shader that combines RGB and spectral shaders. The ranges of common RGB shaders will most probably not match the ranges of the other shader and the simulated light spectrum which will inevitably lead to false results.
  
  
-==== Sensor nodes ==== 
- 
-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 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: 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.  
- 
-<code java> 
-// create a 5cm, white sensor node 
-Axiom ==> SensorNode().(setRadius(0.05), setColor(1, 1, 1)); 
- 
-//check what the sensor node has sensed 
-x:SensorNode ::> { 
-    Measurement spectrum = lm.getSensedIrradianceMeasurement(x); 
-    float absorbedPower = spectrum.integrate(); 
-    ... 
-} 
-</code> 
  
  
Line 395: Line 403:
 </code> </code>
  
 +GroIMP supports the inport of 'Spectral Distribution Files, *.spd' as input for spectral curves, and 'Luminance Files, *.lum' as well as 'IES Light Distribution Files, *.ies' as inport formats for PLDs.
  
 ==== Example ==== ==== Example ====
Line 433: Line 441:
 </code> </code>
  
-The model will run and directly when saved, creates an instance of the light model, set wanted parameters and run it. there will be no output (except the one form the light model itself, stating that it was executed and giving some statistics on the scene). +The model will run and directly when saved, creates an instance of the light model, set wanted parameters and run it. there will be no output (except the one form the light model itself, stating that it was executed and giving some statistics on the scene and further stating that no light sources could be found within the scene). 
  
 If you already get errors here, your system most probably does not support spectral light modelling. If you already get errors here, your system most probably does not support spectral light modelling.
Line 732: Line 740:
  x:TestShader ::> { ms = GPU_LM.getAbsorbedPowerMeasurement(x); }  x:TestShader ::> { ms = GPU_LM.getAbsorbedPowerMeasurement(x); }
  ]  ]
- print("absorbed = "+ms);println(""+ms.integrate()+" = "+ms, 0xff0000);+ print("absorbed = "+ms);println(" = "+ms.integrate(), 0xff0000);
   
  //plot the absorption spectrum  //plot the absorption spectrum
Line 740: Line 748:
 } }
 </code> </code>
 +
 +
 +
 +==== Dispersion ====
 +
 +The GPUFlux light model also supports the simulation of dispersion effects – the phenomenon where light separates into its constituent colours due to variations in the reflective index with wavelengths. Different wavelengths of light refract (bend) at different angles when passing through a medium like glass, causing the colours to separate. Essentially, shorter wavelengths like violet and blue bend more than longer wavelengths like red.
 +
 +As default the simulation of dispersion is turned off - to speed up calculations - but can be enabled in the preferences of the GPUFlux light model or within the code as following:
 +
 +<code java>
 +FluxLightModel LM = new FluxLightModel(RAYS, DEPTH);
 +
 +// enable dispersion
 +LM.setDispersion(true); // default: false
 +</code>
 +
 +
 +When enabled and applied to a scene containing some ‘diamonds’ (imported OBJ objects), one can generate things like shown below (Henke and Buck-Sorlin 2018):
 +
 +{{ :tutorials:dispersion.jpg?direct&600 |}}
  
  
tutorials/basic-spectral-light-modeling.1748892271.txt.gz · Last modified: 2025/06/02 21:24 by MH