Le 19-07-11 à 08:54, scorp08 a écrit :
> Hello All
> For a project, I am using brl-cad (https://brlcad.org) for raytracing stuff.
> What it does is , it emit a particle towards geometry and give output of
> geometry thickness where particle passes, material ID of the geometries ,
> particle vector(direction) etc.
> I am developing a software with python and I want to implement freecad for cad
> works so is it possible to do same thing with freecad as brlcad did using
> raytracing??
> 
> 
> Similar to POVray , I want to define a source that emit light (it can be only 1
> particle or it can be particles which defines an area). Output should contain
> followings:
> - Objects name and material IDs of which being hit by the particle or particles
> from the source
> -thickness of the objects
> -location of hitted points in vector form.
> 
> 
> How can I do that ?
> Do I need a python script also to get material IDs?
> 
> It is similar with povray but in povray, I guess I have to define light source
> as an area only...
> Tnks
> 
> 

In POV-Ray, light sources are defined by location and intensity. They 
are point-light by default. Normally/by default, they don't emit any 
«particle».
It works like this (in an oversimplified way):
Rays are shot from the camera toward the objects in the scene. From the 
intersection between those rays and where they hit something, tests are 
made to determine the illumination by shooting a shadow ray toward the 
light source.
This is called backward ray tracing.

It can be changed using the photons feature where light sources will 
emit «photons» toward target objects. Those photons can reflect on the 
target, or, if the target is transparent, go through the object and get 
refracted according to the IOR as defined for that object.
The number of photon shot is specified by a count value or a spacing, or 
density, parameter.
Normally, photons are shot from a single dimensionless geometric point.

If you want a light to «cover» some area, you need to define it as an 
area_light where you determine it's extant and the number of sampling 
points. This won't affect how photons are shot unless you add
photons{area_light}
to the light's definition.
For your purpose, you should also add the «area_illumination» feature to 
your light.

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