Approximate symmetries of perturbed planar discrete curves

We present a new algorithm to decide whether a discrete curve is symmetric or not. In the affirmative case we assign to each curve a particular symmetry group, and describe all rotational and reflectional symmetries (if they exist). The fundamental strategy of our approach is to decompose the given curve into a collection of appropriate components (simpler discrete curves) whose symmetries can be found more easily. The symmetries of the original curve are then derived from the symmetries of these individual components. Subsequently, we show that the formulated approach can be suitably modified to the situation when the input discrete curve is perturbed. Then we determine the approximate symmetries. The functionality of the proposed method is illustrated by several examples.