This screencast quickly illustrates the concept/idea of a projection. [br][br]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. [br][br]The [b][color=#ff00ff]pink surface[/color][/b] is a [b][color=#ff00ff]part of a sphere[/color][/b] with radius = 4 and with center = (0,0,0). [br]The [b][color=#1e84cc]blue surface[/color][/b] is an [b][color=#1e84cc]equilateral triangle[/color][/b] located within the xy-plane. [br][br]The [b]projection (shadow)[/b] of the [b][color=#ff00ff]pink surface[/color][/b] ONTO the xy-plane IS the [b][color=#1e84cc]equilateral triangle[/color][/b].[br]