Quick AR Illustration: Projection of a Surface onto the xy-Plane
This screencast quickly illustrates the concept/idea of a projection.
Imagine a bright light shining down onto the xy-plane (the plane z = 0). Imagine this light shining down in such a way that the rays of light are perpendicular to this plane.
The pink surface is a part of a sphere with radius = 4 and with center = (0,0,0).
The blue surface is an equilateral triangle located within the xy-plane.
The projection (shadow) of the pink surface ONTO the xy-plane IS the equilateral triangle.