ModuloPrime

StartEdges() and GetNextEdge() control the iteration over edges that will be refined. Default here is to iterate over entire mesh-> Subclasses can override these two functions to restrict the affected edges (eg EdgeLoopFRemesher) We are using a modulo-index loop to break symmetry/pathological conditions. For example in a highly tessellated minimal cylinder, if the top/bottom loops have sequential edge IDs, and all edges are < min edge length, then we can easily end up successively collapsing each tiny edge, and eroding away the entire mesh! By using modulo-index loop we jump around and hence this is unlikely to happen.