Compute the total UVLength/MeshLength ratio along the given VertexPath. Other 3D lengths can then be scaled to comparable UV-space lengths by multiplying by this value. Edges must exist between the vertices along the path, and loops are not considered. Each UV edge for a 3D edge is considered, ie if a 3D edge corresponds to 2 UV edges, both are counted, and if the 3D edge has no UV edges, it is skipped.