Cone-shaped emitter

[buddhasystem]

Dear All,

I'm trying to model a physics process where Cherenkov light is emitter. As a crude first approximation, I would like to experiment with a cone-shaped kind of illumination, and my intention was to use the "spot" emitter with minimum and maximum angles. I could find a reliable way to set this either in the XML code for the scene, or in the Python dictionary afterwards. Any hint or suggestions will be appreciated. Thank you!

[njroussel]

Hi @buddhasystem

The spot plugin provides a cutoff_angle that should allow you to set a maximum angle (documentation). The documentation usually always includes a XML/Python snippet for the initialization, it typically isn't exhaustive -- for breviety not all parameters are used. But by looking at other snippets you should be able to figure out how to add a parameter of a specific type. Finally, in the documentation, each parameter labeled with the "P" flag in the last column will be exposed in Python with mi.traverse(). Parameters without that flag can only be set at initialization.
If you need to be able to set a minimum angle you'll need to either modify the source code of the spot emitter or write your own custom emitter.

[buddhasystem]

@njroussel Thank you! I've looked through the documentation a few times, and there is no example of setting the cutoff_angle in XML. Intuitively, this should be done withing the "rgb" tag just like the intensity, but this produces an error. I've tried a few other things but none works. Is there an example or a template of how to set this?

If I were to do this in Python, will the load from dictionary procedure yield an emitter? Can it then be used to update the scene? Thank you!

[njroussel]

The cutoff_angle is just a float parameter:

<emitter type="spot">
    <.../>
    <float name="cutoff_angle" value="30"/>
    <.../>
</emitter>

In Python, mi.load_dict({'type': 'spot', ... }) will indeed return an Emitter object. However, it cannot be inserted into a scene. The only edits to a scene that can be done is modifying plugin parameters (marked with a "P", as mentioned in my previous comment)

[buddhasystem]

Thank you! It works great.

[buddhasystem]

@njroussel Thanks much. Very helpful.