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In article <[email protected]> [email protected] (Stephen Pietrowicz) writes: |
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>How do you go about orienting all normals in the same direction, given a |
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>set of points, edges and faces? |
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Look for edge inconsistencies. Consider two vertices, p and q, which |
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are connected by at least one edge. |
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If (p,q) is an edge, then (q,p) should *not* appear. |
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If *both* (p,q) and (q,p) appear as edges, then the surface "flips" when |
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you travel across that edge. This is bad. |
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Assuming (warning...warning...warning) that you have an otherwise |
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acceptable surface - you can pick an edge, any edge, and traverse the |
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surface enforcing consistency with that edge. |
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0) pick an edge (p,q), and mark it as "OK" |
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1) for each face, F, containing this edge (if more than 2, oops) |
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make sure that all edges in F are consistent (i.e., the Face |
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should be [(p,q),(q,r),(r,s),(s,t),(t,p)]). Flip those which |
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are wrong. Mark all of the edges in F as "OK", |
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and add them to a queue (check for duplicates, and especially |
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inconsistencies - don't let the queue have both (p,q) and (q,p)). |
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2) remove an edge from the queue, and go to 1). |
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If a *marked* edge is discovered to be inconsistent, then you lose. |
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If step 1) finds more than one face sharing a particular edge, then you |
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lose. |
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Otherwise, when done, all of the edges will be consistent. Which means |
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that all of the surface normals will either point IN or OUT. Deciding |
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which way is OUT is left as an exercise... |
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Kenneth Sloan Computer and Information Sciences |
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[email protected] University of Alabama at Birmingham |
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(205) 934-2213 115A Campbell Hall, UAB Station |
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(205) 934-5473 FAX Birmingham, AL 35294-1170 |
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