• Assume we have a line starting in the origin and going at a 30° angle to the right, relative to the forward camera axis (Y).
• Since parallel lines have the same vanishing point, this means that all lines at a 30° angle, including this one going through the viewpoint, will converge to the same place point.
• And since this line intersects the picture plane at some point, and the vanishing point is on the picture plane, then the vanishing point we are looking for is precisely the intersection of this line with the picture plane.

• Now to actually be able to measure this 30° angle accurately on paper, we take the triangle formed by the vieweing direction, the 30° line going through the viewpoint, and the line from the 30° VP to the PP, and then rotate it around the X axis of the picture plane until the viewpoint hits the picture plane.
• The result is the same triangle, now sitting on the picture plane, and a point on the picture plane that mirrors the angles made from the viewpoint. This point is called the Station Point (SP).

Horizontal SP (HSP), in fact, since we can use the same reasoning to obtain the station point for vertical angles -> Vertical Station Point (VSP).