public void CalculateFlatNormals()
{
if (!(this.Owner is Mesh mesh))
{
throw new InvalidOperationException();
}
this.Normals.Clear();
this.MappingMode = MappingMode.ByPolygon;
this.ReferenceMode = ReferenceMode.Direct;
foreach (Polygon item in mesh.Polygons)
{
XYZ normal = XYZ.FindNormal(
mesh.Vertices[item.ToArray()[0]],
mesh.Vertices[item.ToArray()[1]],
mesh.Vertices[item.ToArray()[2]]);
this.Normals.Add(normal.Normalize());
}
}