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### #Actualdeekr

Posted 11 February 2013 - 01:54 AM

I don't think this problem is well-defined, or at least the language isn't all there. In general, the result of a cross-product is a vector. The "sign" doesn't make much sense in arbitrary 3D, without a reference. You mentioned a "normal direction", but what does this mean? The edges could be on two different faces, maybe on two different rigid bodies, maybe the normal direction is the screen, ...

However, it does sound like you are trying to compare the "orientation" or "handedness" of these two vectors with respect to some direction, which makes sense to me. In this case, cross the two edges and then dot the result with the direction (do all of this in some consistent order). Positive means one way, negative means the other, zero is indeterminate.

edit: (assuming the two vectors are not degenerate)

### #1deekr

Posted 11 February 2013 - 01:52 AM

I don't think this problem is well-defined, or at least the language isn't all there. In general, the result of a cross-product is a vector. The "sign" doesn't make much sense in arbitrary 3D, without a reference. You mentioned a "normal direction", but what does this mean? The edges could be on two different faces, maybe on two different rigid bodies, maybe the normal direction is the screen, ...

However, it does sound like you are trying to compare the "orientation" or "handedness" of these two vectors with respect to some direction, which makes sense to me. In this case, cross the two edges and then dot the result with the direction (do all of this in some consistent order). Positive means one way, negative means the other, zero is indeterminate.

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