Discrete Invariant
The normalization of the curve parameter s was selected above so that
If n≡0 (mod 4) or n≡3 (mod 4) then the sign of this determinant is a discrete invariant of the curve. A curve is called dextrorse (right winding, frequently weinwendig in German) if it is +1, and sinistrorse (left winding, frequently hopfenwendig in German) if it is −1.
In three-dimensions, a right-handed helix is dextrorse, and a left-handed helix is sinistrorse.
Read more about this topic: Affine Geometry Of Curves
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