public void Contract(ECVertex v1, ECVertex v2, Point3d to)
{
temp.Clear();
ContractRegion(v1, v2, temp);
RelocateVertex(v1, to.X, to.Y, to.Z);
v2.ReplaceBy(v1);
RemoveDegenerateFaces(temp);
}
public void ReplaceVertex(ECVertex from, ECVertex to)
{
from.ReplaceBy(to);
}