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shadow calculation for a point light source

skybrianskybrian Member Posts: 24
I drew a point for the location of a point light source, and on another sketch plane I drew a window. I'd like to cast a shadow through the window, projecting each point of the window onto a third sketch plane. Is there some nice way to do this sort of point projection? It's easy to draw construction lines to do this projection in 2D, but how about 3D?

Best Answers


  • NeilCookeNeilCooke Moderator, Onshape Employees Posts: 4,163
    Not from a point light source, but this script will create a directional light source https://forum.onshape.com/discussion/11011/silhouette-outline
    Director, Technical Services, EMEAI
  • S1monS1mon Member Posts: 632 PRO
    If you had a Pro license, you could use Render Studio. 
  • skybrianskybrian Member Posts: 24
    Neither of these are quite what I'm looking for. How about I put it another way: Suppose I have a point on one sketch plane and a polygon drawn on a parallel sketch plane. Is there some way I can use this to define a pyramid-shaped part, by projecting lines from the point through each corner of the polygon? The shape of this part is the shape of the light beam.

    Loft seems sort of like this, but I don't see any way to project lines from a point.

    One way I figured out is to use "3D fit spline" repeatedly to create line segments, and then "Fill" repeatedly to create faces. After which I suppose they could be turned into a part. Here is a start: https://cad.onshape.com/documents/bf2ca947dc0c9788a3c8c3d2/w/673af95005e00c5e5df00cda/e/ffb28a086a97b23fb4d4f677

    It seems tedious, though. Also, the next step would be to project the face further, beyond the the polygon. Perhaps creating a 3-point plane for each face of the pyramid would be better, but that's a lot of planes.

    (By contrast, a directional light source seems easy enough - that's just ordinary projection to a sketch that's perpendicular to the light direction. Then extrude.)
  • NeilCookeNeilCooke Moderator, Onshape Employees Posts: 4,163
    Answer ✓
    So, it's not really got anything to do with light sources at all? Loft to point is what you need. Here's an example: https://cad.onshape.com/documents/b69cae1e6260585fa084dc46/w/50d6d78e8af0e5b7adebe5b8/e/74861788c4703f4ffd832663
    Director, Technical Services, EMEAI
  • skybrianskybrian Member Posts: 24
    Yes, thanks! I'm drawing a light, not actually doing any lighting.

    This is probably good enough, but ideally for the next step, I would like to extend the pyramid to intersect a third plane. I set up an example in a second Feature Studio: https://cad.onshape.com/documents/bf2ca947dc0c9788a3c8c3d2/w/673af95005e00c5e5df00cda/e/42db0ce3068e576d24f42a15

    Is there a nice way to extend the pyramid to go from Window to Target via projection (rather than sketching something on Target)? 
  • NeilCookeNeilCooke Moderator, Onshape Employees Posts: 4,163
    Answer ✓
    Yes! Simple way = Move face or Replace face.
    Director, Technical Services, EMEAI
  • skybrianskybrian Member Posts: 24
    Thanks! (Replace Face seems better here since it will project to an arbitrarily oriented plane.)

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