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# polygon planarity?

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How would I determine whether a polygon with more than 3 vertices (i.e., say 5 vertices (1,2,3),(2,3,4),(3,4,5), (4,5,6),(5,6,7)) is "planar", and what exactly is the significance of that? If I got the cross product of say two sets of vertices (i.e., say v1,v2,v3, and then v2,v3,v4) -- would some sort of comparison work? Or is there something else? Thanks!

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the cross product vectors must be parallel (due to float imprecisions they will often be not exactly but only close to parallel).
most renderers will triangulize the polygon so you''ll end up with non-coplanar triangles; there are different triangulizations for a given polygon so it''s not guaranteed that the polygon will always look the same way.
secondly, i don''t know what your application is, but designers will want something being called polygon to be flat.

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