int tpos1 = pos1, tpos2 = pos2;
// skip past all cpoints at the same position
for(left_same = ++iter1; iter1 != end() && (*iter1).pos == left.pos; iter1++, pos1++)
int tpos1 = pos1, tpos2 = pos2;
// skip past all cpoints at the same position
for(left_same = ++iter1; iter1 != end() && (*iter1).pos == left.pos; iter1++, pos1++)