I am interested in the complexity of this problem:
Input: Given N points on integer 2D grid (N is even)
Question: Can we construct an orthogonal simple polygon from the set of N mid–points?
Each mid–point (an (x,y) pair with integer coordinates) is the midpoint of exactly one side; the polygon has N sides and its sides are all axis–parallel.
Does it become easier if no two mid–points share an x– or y–coordinate?
I know that the problem is NP-complete if each point is located at general position on a side excluding polygon's vertices.