This article shows how to create a scattering file in Speos format based on raw measurement data. The Speos *.scattering format models the reflectance, transmittance and absorption of a surface as a function of the wavelength and the incident angle. It is used to define surface optical properties in Ansys Speos.
Note: Another format, the Speos *.simplescattering format, also models the reflectance, transmittance and absorption of a surface but independently of the wavelength and the incident angle.
Overview
The following data is needed to create a scattering surface file:
- Reflectance
- Specular [%]
- Lambertian [%]
- Gaussian [%]
- FWHM* in incidence plane [deg]
- FWHM* in parallel plane [deg]
- Transmittance
- Specular [%]
- Lambertian [%]
- Gaussian [%]
- FWHM* in incidence plane [deg]
- FWHM* in parallel plane [deg]
- Absorption [%]
Each of these values are expressed in function of the wavelength [nm] and the incident angle [deg].
The data can either be processed in the Advanced Scattering Surface Editor, requiring a Speos license, or in plain text format *.txt in any text editor. Any change in the text file will be reflected in the Advanced Scattering Surface Editor interface when saved with the *.scattering file extension.
The resulting *.scattering file will then be used in Speos as input to model surface optical properties.
*FWHM: Full width at half maximum is a statistical measure used to describe the width of a normal distribution or Gaussian distribution. Specifically, it represents the width of a curve measured between the two points where the curve's value is half its maximum
File format details
Let’s take an example to understand how values are processed.
- The first section, marked in red, corresponds to values for a wavelength of 400nm and an incident angle of 0°. The contributions are the following ones:
- 30% of specular reflection
- 20% of Lambertian reflection
- 20% of specular transmission
- 10% of Lambertian transmission
- 20% of absorption to reach a total of 100%
If you display the scattering surface curve by clicking the button highlighted in green, you can distinguish all the contributions: the specular contribution represented by an arrow and the Lambertian contribution represented by a sphere.
Section 1
- The second section, marked in red, corresponds to values for a wavelength of 600nm and an incident angle of 45°. The contributions are the following ones:
- 20% of Gaussian reflection with a FWHM of 30° in the incident plane and 5° in the perpendicular plane
- 20% of Gaussian transmission with a FWHM of 5° in the incident plane and 30° in the perpendicular plane
- 60% of absorption to reach a total of 100%
If you display the scattering surface curve by clicking the button highlighted in green, you can observe the Gaussian contribution with the different FWHM values:
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- In the incident plane, we can see that the angle is 30° for the reflection and 5° for the transmission
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Section 2
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- In the perpendicular plane, we can see that the angle is 5° for the reflection and 30° for the transmission
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Section 2
Information on the parameters
- There must be at least two incident angles: 0° and 90°. The additional values must be between 0° and 90°.
- There must be at least two wavelengths.
- The FWHM for the Gaussian contribution must be between 0° and 90°.
- The absorption value is auto-filled to reach 100%.
- The sum of the reflectance contribution and the transmittance contribution must be inferior or equal to 100%. If it is not the case, then the absorption value is negative, and the cell will be displayed in red with an error message.
Here is the structure of the file, if opened in a text editor:
Row 1 |
OPTIS - Scattering surface file v1.0 |
Header (not to be changed) |
Creation of the file using a spreadsheet editor
A first solution to create a file is to use a spreadsheet editor, copy-paste the content in a text editor and save it with the *.scattering extension. This solution does not require a Speos license.
The example below can be copied and pasted into a spreadsheet editor.
OPTIS - Scattering surface file v1.0 | ||||
Scattering surface | ||||
3 2 | ||||
400 | 600 | |||
0 | 30 | 20 | 0 | 0 |
20 | 10 | 0 | 0 | |
0 | 0 | 0 | 0 | |
0 | 0 | 0 | 0 | |
0 | 0 | 0 | 0 | |
45 | 0 | 0 | 0 | 0 |
0 | 0 | 0 | 0 | |
0 | 0 | 20 | 20 | |
0 | 0 | 30 | 5 | |
0 | 0 | 5 | 30 | |
90 | 0 | 0 | 0 | 0 |
0 | 0 | 0 | 0 | |
0 | 0 | 0 | 0 | |
0 | 0 | 0 | 0 | |
0 | 0 | 0 | 0 |
Example of a file in a spreadsheet editor
The following image shows the same file in a text editor
Example of a file in a text editor
Creation of the file using Advanced Scattering Surface Editor
- The following solutions require a Speos license.
- The following solutions can be combined to create one file.
Using the spreadsheet
The Advanced Scattering Surface Editor can be used to create the file by simply entering the values manually in the editor.
To add or remove incident angles and wavelengths, use the following buttons
Using the Autofill tool
The Autofill tool is accessible by clicking on Tools / Autofill…
Then, there are three different options available:
- Spectrum Import
- Fresnel contribution
- Apply a value to a selection of cells
1. Spectrum Import
You can select a *.spectrum file and use it to define the values of any parameters. This method will fill the file with the values of the spectrum according to the wavelengths but independently of the incident angles. Please refer to the Speos Labs User’s Guide for more information on spectrum parameters: Parameters of a Spectrum
Here is the process step by step to use this option:
- Browse a spectrum file
- Select the contribution type
- Select a “wavelength sampling” option
- Use spectrum sampling: the number and values of wavelengths will be the ones from the spectrum file
- Use current sampling: the number and values of wavelengths will be the ones defined in the current opened file. In that case, interpolation will be applied to fit the sampling.
- Select an “other properties” option
- Put other value to 0.0: every other contribution will be set to 0
- Define value for other properties: you can set a value for every other contribution thanks to the spreadsheet on the right. These values will be the same for all wavelengths.
- Keep other value unchanged: the values of other contributions will remain the same. This option is useful if you want to use several spectrums to define several contribution types.
2. Fresnel contribution
You can select a *.material file and use it to define the values of any parameter. This method will fill the file with the Fresnel coefficients according to the indexes defined in the material file. The values will depend on the wavelengths and on the incident angles.
Example of a material file that can be used:
Here is the step-by-step process to use this option:
- Browse a material file
- Select a polarization option (the Fresnel coefficients depend on the polarization):
- Parallel
- Undefined: it is the average of parallel and orthogonal polarization values
- Orthogonal
- Select either Specular Reflection or Gaussian Reflection
- Tick one or several options:
- Thick transparent: this option will consider the inter-reflections that can be present into a volume, the reflection value will then be higher
- Fill transmission: to fill the transmission contribution in the file in addition to the specular or Gaussian reflection
- Multiply Lambertian reflection by Fresnel transmission: this option is only available if the other two are not ticked. It multiplies the Lambertian reflection defined in the file by the transmission coming from the Fresnel coefficients
3. Apply a value to a selection of cells
This method simply helps you fill the spreadsheet faster. You can define a constant value for any contribution, for a specific or for all wavelengths and for a specific or for all incident angles.
Additional Resources
- Advanced Scattering Surface Editor (ansys.com)
- Speos BRDF, BTDF and BSDF Formats – Ansys Optics
- Convert 2D measurement data into Speos 3D BRDF file – Ansys Optics
- Speos Non-Scattering Volume Format – Ansys Optics
- Speos Scattering Volume Format – Ansys Optics
- Optical Automation library introduction – Ansys Optics
- Speos Coating Surface Format – Ansys Optics
- Book a measurement at Opsira.de