The further apart from each other they are drawn, the farther back they appear to be. The realization of stereographics is based upon these principles. The darker the points become the deeper they are in the stereographic. The second assumption is the so called starting-stripe being as high as the picture is but only 2 to 4 cm in width. Approximately and not precisely because the distance to copy has to be slightly corrected all the time.
Darker points lead to an increase.
Step by step calculating every point after the other, using a simple algorithm the stereographic appears after seconds on the screen.