# Finding out which face corresponds to which

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I am trying to figure out how to be able to sample the materials of a more high res model and apply them to the low poly version in the most accurate way. I know everything except the math part. Namely how to get what face corresponds to each face in the low res model. I cant just take face who's center is closest and i am thinking i should take the normals into consideration as well. Any suggestions would be greatly appreciated!!

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Assuming no polys in the hi-res model correspond to more than one poly in the low-res one, I´d try this:

For each poly i in the low-res model:
- calcluate the plane Pi it lies in
- For each poly j in the hi-res model:
-- Project j on Pi. Also remember a distance d_ij of j from Pi (I´d try average distance of j´s points).
-- if projection lies within Pi mark it as possible possession of j.

Now, the problem is that for polys j it´s possible to meet the "possessed by" criteria of more than one poly i. That´s why a 2nd step is nessecary to determine which of the possible owners j has. This one would be as simple as:
j belongs to the poly i that it´s closest to: Owner = i: d_ij=min.

That´s just my first guess what I´d do. There may be professional algorithms that are better or it might be able to simplify above. It will probably not work if polys of the hi-res model do not project into a poly of the low-res model. I assumed you get the low-res model by removing points from the hi-res one. It should give ok results, then.

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