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*On 30/01/2011 at 06:08, ***xxxxxxxx** wrote:

Hmm, but poly-normals are calculated from the polygon's points as well?

Basically, a point has no normal. It cannot, because a single point does not define a three-dimensional base system. The idea "a point's normal is the median of the polygon's normals where the point is a part of" is an artificial definition that has certain advantages.

A polygon's normal is the vector that is orthogonal to the plane of the polygon. The plane of a polygon is defined by two of its sides forming a two-dimensional (not necessarily orthogonal) base system. (Note that a polygon in C4D is not necessarily plane; for mathematical calculations on 4-or-more-point polygons you need to assume that the points of the polygon are coplanar, and that the edges defining the plane are not collinear/parallel.)

The normal for a polygon is then calculated by the (normalized) cross product of the two edges (vectors) that define the polygon plane. Note that the sequence of points is relevant to get the normal pointing into the right direction.

So, if you have a polygon P made from points ABC, then Norm(AB x AC) will be your normal (or is it AB x BC? too lazy now to look it up...) Therefore, your normal IS calculated from the points.

Can you calculate the normal from the direct neighbors without looking at the polygons? No! The polygons will deliver the information which neighboring points are actually necessary for calculating one of the normals involved in getting the central point's normal. I could show you some examples where an "intuitive" calculation fails, and not all of them are based on "evil" polygon configurations. And even if you could (in certain cases there are working algorithms...), it would NOT be faster than getting the normals of the polygons.