public static List <DS.Surface> SurfacesFromPointAndDirection(List <DS.Surface> surfaces, DS.Point viewPoint, DS.Point targetPoint)
{
DS.Vector viewVector = DS.Vector.ByTwoPoints(viewPoint, targetPoint).Normalized();
List <DS.Surface> visibleSurfaces = new List <DS.Surface>();
foreach (var surface in surfaces)
{
DS.Vector normal = surface.NormalAtParameter(0.5, 0.5);
double dot = normal.Dot(viewVector);
if (Math.Round(dot, 6) <= 0)
{
visibleSurfaces.Add(surface);
}
}
return(visibleSurfaces);
}