Barend Gehrels wrote:
What should the generic "area" algorithm return for point and linestring? What should the generic "length" algorithm return for polygon? What should the generic "centroid" algorithm return for point and linestring?
There are two cases I can think of here: - Maybe I have a heterogeneous collection of geometric objects and I want to do something involving one of these algorithms to each element. I can't imagine doing this in a real scenario, so I have no comment about what the behaviour should be. - I have made a typo in my code. In this case I really want a compiler error.
and for an invalid polygon (e.g. no points at all, or not closed)?
One option is to prohibit invalid polygons, i.e. to make it impossible to construct one with too few points. I suspect that this would lead to other problems though. So I suggest that you have a simple is_valid() test that the user can call if they care about this case and make centroid (etc) return an arbitrary answer like (0,0), but guarantee not to crash (e.g. not divide by zero). Phil.