Hi, Adam thanks for the reply and detailed code and explanation. Yes, it worked.

I implemented as per your instructions but encountered a small problem. That is sometimes I realized the intersections points between the linestrings and the polygon are not in a "consistent" order, e.g. as shown in the below image, lingstring 1 has P1->P2; However, instead of P3->P4, linestring 2 is P4->P3. I actually expect linestring 2 is also along P3->P4 direction. Is this how it is supposed to be? Any workaround to solve this problem? Thanks.