Defining Properties
Display Values
Select the curves to plot. Polarization and temperature can modify the curves dependent on the level of data entered for these parameters. Without polarization selection, some curves cannot be plotted.
Polarization |
Select by checking one or more check boxes for Ave (Average), S (S-axis), |
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and P (P-Axis). |
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Curves |
Select by checking one or more check boxes for Refl (Reflection), Tran (Trans- |
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mission), and Abso (Absorption). |
Temperature |
Type the Temperature in Kelvin into the text entry box. |
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Table BSDF Expert
TracePro supports two types of tabular BSDF models: Table BSDF and Asymmetric Table BSDF. To use the Table BSDF model, you enter a table of BSDF values versus the radial component of |β-β0|. See “Harvey-Shack BSDF”
on page 7.16. During the ray-trace, TracePro linearly interpolates between the tabulated values. To use the Asymmetric Table BSDF model, you enter a twodimensional table of BSDF versus the radial and azimuthal components of |β-β0|.
During the ray-trace, TracePro bilinearly interpolates the two-dimensional table to determine the BSDF. Selection of a Table BSDF model is independent of whether the TracePro Surface Property is anisotropic.
Creating a Table BSDF Property
To create a surface property with Table BSDF:
1.Select Define|Edit Property Data|Surface Properties to open the Surface Property editor window.
2.Choose a catalog from the catalog dropdown list.
3.Click on Add Property. When the Enter New Surface Property dialog box is displayed as shown in Figure 3.16, select Table BSDF from the Scatter Model list, enter a name for your new property and values for initial angle and initial wavelength, then click OK.
4.Edit the other values simply by selecting a value and making changes.
5.Select File|Save from inside the Surface Property editor window or close the Surface Property editor and answer yes to the question “property has changed, save data?” Your new property is now available in the Property Database for future use.
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Surface Properties
FIGURE 3.16 - Selecting Table BSDF from the Scatter Model list in the Enter New Surface Property dialog box.
The new Table BSDF surface property will be displayed in a spreadsheet as shown in Figure 3.17.
FIGURE 3.17 - Surface Property editor created with Table BSDF type.
On the right side of the spreadsheet are columns for Scatter Beta, BRDF, and BTDF. The Scatter Beta column provides values of |β-β0| for tabulating both the
BRDF and the BTDF. These values are independent of the Incident Angle values for the surface property. The first row for a provided incident angle (shown in the 3rd Column) provides the integrated BRDF and BTDF for this angle. The integrated BRDF and BTDF is the total scattered flux into a hemisphere from the surface normal. The rows following the integrated amount represent |β-β0| values
and the respective BRDF and BTDF at these angular offsets from the specular direction. See page 7.15 for more details about this process.
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Defining Properties
To add more |β-β0| rows, click Add to open the Surface Property – Add Data Dialog dialog box as shown in Figure 3.18. Select Scatter Beta, enter the |β-β0| value in the dialog box (the value 0.01 is shown) and click OK.
FIGURE 3.18 - Adding a new value of |β-β0| to the BSDF table.
You can add as many Scatter Beta values as you wish. You may find it easier to create a template for the Table BSDF property and export it to a text file, fill in the BSDF values, and import the property. This is usually easier than typing in all the BSDF values in the Surface Property spreadsheet. This requires nine steps:
1.Create a Table BSDF surface property with a value of |β-β0|. Add some of the data that will be needed by the property. This data will act as a template in the following steps.
2.Save the property into the database using File|Save.
3.Export the property to a text file using File|Export. The result is a tabdelimited text file, which works best with spreadsheet programs such as Microsoft Excel.
4.Import the file into a spreadsheet program like Excel. (Figure 3.19 shows our example property imported into Excel. There are more columns to the right in the property, but we do not need to view them for our example.)
5.Fill in new values for Scatter Beta, BRDF, and BTDF per your available data. Figure 3.20 shows our example with BRDF data only, suitable for a mirror.
6.Save the text file and close Excel.
7.Import the text file in the Surface Property Editor using File|Import, as shown in Figure 3.21.
8.Enter values for the other property table coefficients, e.g. absorptance, specular reflectance and specular transmittance.
9.Use the Solve for feature, if necessary, to make the property conserve energy. The completed example surface property is shown in Figure 3.22.
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Surface Properties
FIGURE 3.19 - Table type surface property with Table BSDF model after importing into Excel.
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Defining Properties
FIGURE 3.20 - Surface property after filling in example values for |β-β0| and
BRDF.
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Surface Properties
FIGURE 3.21 - Example table BSDF after importing back into the Surface Property Editor. TracePro has computed the Integrated BRDF.
FIGURE 3.22 - Table BSDF surface property after entering 0.05 for absorptance and solving for Reflectance. The property is complete and ready for use.
You can use the Solve For feature to compute the BRDF and BTDF with a Table BSDF model, but you must enter factors into each of the BRDF or BTDF cells. These factors represent the ratio of the actual BRDF or BTDF values in the cells upon computation due to the Solve For. This process will ensure energy conservation while allowing the user to ignore the complexity of doing the rigorous calculations.
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