Point projective and permutation invariants
The paper deals with features of a point set which are invariant with respect to projective transform. First, projective invariants for five-point sets, which are simultaneously invariant to the permutation of the points, are derived. They are expressed as functions of five-point cross-ratios. Possibilities of the choice of their roots are referred and their normalization is discussed.
Then, the invariants for more than five points are derived. Stability and discriminability of the features is demonstrated by numerical experiments.
KeywordsConvex Hull Projective Invariant Point Projective Imaginary Root Configuration Invariant
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