public override int GetHashCode()
{
if ( isNull )
return 0;
return corners[ 0 ].GetHashCode() ^ corners[ 1 ].GetHashCode() ^ corners[ 2 ].GetHashCode() ^ corners[ 3 ].GetHashCode() ^ corners[ 4 ].GetHashCode() ^
corners[ 5 ].GetHashCode() ^ corners[ 6 ].GetHashCode() ^ corners[ 7 ].GetHashCode();
}