Retroreflection
There are multiple ways to model retro reflection in FRED. Here are some examples:
A Corner Cube:
Using a corner cube prism is a very simple way to create a retroreflector. The advantage of using a corner cube prism is that it is suitable for both incoherent and coherent raytracing, and also will keep track of polarization changes. For users who have FREDmpc version it can also be included in GPU raytraces.
Surface with scripted Scatter model:
The performance of a retroreflective material can sometimes be represented by a BSDF model (typical for the type of retroreflectors made up of microscopic glass beads). This is often obtained from measuring a sample. This reflected BSDF peaks at the angle of the incident ray and falls away very sharply. One way to achieve this in FRED is to use the Scripted Scatter model.
In this example the BSDF is of the form A * | cos(scatter) - cos(incident) | ^ n.
The advantage of this method is that it's possible to "tune" the scripted scatter model via the "A" and "n" parameters to match the measured data. However, note that this will only be suitable for incoherent raytracing, and not suitable for the GPU raytrace of FREDmpc which doesn't yet support scripted scatter.
Raytracing the arrayed structure:
For users who want to model a prismatic retroreflective sheeting made up of an array of corner cube prisms, the most suitable option is to build the structure in FRED to the desired specifications, therefore allowing both incoherent and coherent raytracing, and keeping track of polarization effects.
FRED's Array feature can be used to simplify this process, or it can be created as a collection of individual prisms if it is required to raytrace this on the GPUs using FREDmpc. In the screenshot below the source is highlighted in the red box, and incident at 15 degrees.
