Mesh shadow operation randomly failing

Hello everyone,

I have a question regarding mesh shadow operation in grasshopper. I’m posting in serengeti, though, because I mostly use the WIP, and because the problem I have also manifests in R7.

I’ve been dealing with what seems to be a glitch that’s somewhat of a headscratcher.

When dealing with mesh shadows I get a failed result (appears to be arbitrary) - with the only error message “shadows were not cast onto the plane”.

Here’s my situation:

  1. I have 18 meshes floating in space in a somewhat spherical distribution:

They’re all the same mesh, oriented to multiple locations.

  1. I have a bunch of planes (x92) corresponding to specific collisions between each mesh and 92 objects:

  1. Using the data from the planes, I generate shadows as I’m in need of their projected outlines at each specific location:

  1. However for some reason at least one of the shadows fails for no reason.
  • here’s a close-up of said failing shadow-plane:

  • nothing really different from all the other meshes/planes other than their location…

  • here’s the sinister bug in action:

  1. Interestingly, if I move the mesh in any direction by a miniscule amount (like 0.001), the shadow works:


Yes, why not just move the failed ones a miniscule amount and problem solved, right?

Well that’s exactly what I’m doing, however it’s not convenient for the precise fabrication this is intended for.

Another work-around at the moment is literally projecting the mesh to the plane:


Why not just do this for all meshes, right?

Because: It’s unpredictable; if I do exactly that what happens is I get new mesh shadow errors which will require more work-arounds.

Definitely a head-scratcher.

Why does this happen?

I appreciate your feedback.

Here’s the file with the sample if it matters: (862.5 KB)


I don’t really know why this is happening, put I’ve tested your sample file with the definition from this other topic, and outlining seems to work great.

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Thanks a lot for looking into it @diff-arch ! I appreciate it and I agree. This is the way to go for it now.

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The thing is, the Rhino MeshOutline is reliable while the GH Mesh Shadow isn’t.
That sucks because the ability to choose a vector and a receiving plane is really useful…