void CalculatePlaneEquation()
{
double len;
int i;
Vector3d ref1, norm, v1, v2;
Point3d vert1, vert2;
ref1 = new Vector3d();
norm = new Vector3d();
v1 = new Vector3d();
v2 = new Vector3d();
for(i=0; i < m_points.Length; i++)
{
vert1 = m_points[i];
vert2 = m_points[(i+1) % m_points.Length];
v1.x = vert1.x;
v1.y = vert1.y;
v1.z = vert1.z;
v2.x = vert2.x;
v2.y = vert2.y;
v2.z = vert2.z;
norm.x += (v1.y - v2.y)*(v1.z + v2.z);
norm.y += (v1.z - v2.z)*(v1.x + v2.x);
norm.z += (v1.x - v2.x)*(v1.y + v2.y);
ref1.x += v1.x;
ref1.y += v1.y;
ref1.z += v1.z;
}
len = norm.Mag();
plane.a = norm.x / len;
plane.b = norm.y / len;
plane.c = norm.z / len;
len *= m_points.Length;
plane.d = -ref1.Dot(norm) / len;
}