// get a tanget of an egde, at point v
Vector3d GetTanget(int v, int v1)
{
EdgeAmf edge = m_pointList[v].FindEdge(v1);
if (edge != null)
{
return(edge.t1);
}
edge = m_pointList[v1].FindEdge(v);
if (edge != null)
{
return(Vector3d.negate(edge.t2));
}
Point3d pt1 = m_pointList[v].pt;
Point3d pt2 = m_pointList[v1].pt;
return(new Vector3d(pt2.x - pt1.x, pt2.y - pt1.y, pt2.z - pt1.z));
}