Mesh projection culling

Hi, I'm wandering what would be a good and fast approach to cull the stretched mesh face resulting from a planar mesh projected on a 3d object and only leave the face that are coplanar to the intersecting mesh?

I've had good result by pushing the new mesh further with a Wb offset and then shooting back at the intersecting mesh using the mesh face normals to get a cull pattern.
But I'm sure there are better ways?

Thanks!

Francois

Tags: Projection, exposure, isovist

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Permalink Reply by Danny Boyes on March 21, 2012 at 11:50am

I would cull based on the Perimeter Length of a Face. The smallest Face Perimeter would be the "Camera Plane" and the largest would be the stretched faces so anything in between would be the co-Planar. (In theory)

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Permalink Reply by Andrew Heumann on March 21, 2012 at 1:17pm

Not sure if this is any faster, but you could take the meshface centers (with the face normals component) and test for the BRep closest point and cull by distance.

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Permalink Reply by Francois on March 21, 2012 at 1:38pm

Hi Andrew, sound really good!

You think it would still work when the intersecting object is a complex hi-rez mesh?

Thanks

Francois

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Permalink Reply by Francois on March 21, 2012 at 1:26pm

Nice, thank you Danny! I did try your technique, it works nice.

Depending on the shooting point placement, some of the rays will hit the mesh at a great angle creating a larger perimeter even when the surface is expose...

My goal is to create a accurate 3D mapped exposure matrix area for photometric analysis.

Regards

Francois

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Permalink Reply by Francois on March 21, 2012 at 1:57pm

If anyone is interested, here is the work in progress definition.

grasshopper/PlanarMesh-Projection_20120321.gh

Regards

Francois

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Permalink Reply by Francois on March 27, 2012 at 2:41pm

I have a setup that is working pretty good using Mesh/curve intersect.
I do the intersect on a positive and a negative offset and I compare to make sure I don't cull the faces that are exposed but are sitting on a corner of the mesh.