This walkthrough is inspired by an article on Creative JS. The demo shows how to convert 3D points into screen coordinates. Here we create a very simple particle system using 1 pixel dots rendered on a horizontal flat surface.
The 2 important factors controlling the appearance of a 3D projection are - field of view which is basically the zoom level or how far the elements are from us and the z-coordinates which determine the scaling/positioning of the elements on a 2d plane(the screen).
This article gives an excellent explaination of the geometry behind perspective projection.