Source: http://www.ests.um5.ac.ma/cours/Dipl%C3%B4me%20Universitaire%20de%20Technologie/G%C3%A9nie%20Civil/Semestre%2002/Dessin%20assist%C3%A9%20par%20ordinateur/Cours%20Dessin%20Assist%C3%A9%20par%20Ordinateur%20(DAO).pdf