public static double ComputeWallwalkAngle(Point start, Point intersection, Edge wall)
{
// Compute the angle needed to turn in order to walk parallel to the wall,
// with your right hand on it.
Point heading, end;
Edge compare;
end = wall.P1;
heading = start + end - intersection;
compare = new Edge(intersection, heading);
if (compare.CrossProduct(end) > 0)
{
end = wall.P2;
heading = start + end - intersection;
compare = new Edge(intersection, heading);
}
return Math.Atan2(end.Y - intersection.Y, end.X - intersection.X) -
Math.Atan2(intersection.Y - start.Y, intersection.X - start.X);
}