[pstricks] How work psdiabox, pstriabox, psovalbox and pscircle

[ARno]

Hi,
I am working on a graphical pstricks generator 
(http://latexdraw.sourceforge.net/)
and I want to want know how the psdiabox, pstriabox, psovalbox and 
pscircle commands are made; i.e., how the width and the height of the 
triangle, the diamond, the circle and of the ellipse are computed. I am 
not conversant with the code of the pstricks.tex file.

Best regards,
Arnaud BLOUIN