QUOTE (oliverandjazz @ Jul 18 2009, 02:27 PM)

thats a great photo cees..

We often have to draw in perspectives regular vertical (or horizontal) lines, for examples windows or gates (see the first figure below). How to proceed ?
To understand the principle, consider the simple case of a rectangle divided vertically into 2 or 3
equal parts (see the second figure).
In perspective, if we draw the vertical divisions exactly in the middle, or in the proportions 1/3, 2/3, as shown in the second figure, it is of course incorrect.
If you know how to proceed
mathematically in these two examples, you can approximately draw in more complicate situations.
The division by 2 is simple, the division by 3 is less simple. Who has the answers ?