I would like to do some precise vertex positionning with regard to the 3D cursor, eg put a vertex at coordinate (0.1,0.1,0.1) from 3D cursor (which I can position very easily to a convenient position). Is that possible? I am not talking about the local coordinate system, which takes the object's origin as origin.
Xavier, you can position a selection at a set of coordinates in the edit menu by using the 3D cursor location on the Properties menu N. You can then move a selected point to the cursor location using the Snap menu Shift+S and selecting "Selection to Cursor" This positions the selection using the global coordinate system. You can also enter the coordinates of the active vertex directly using that same menu. Beneath the coordinates, you specify weather the location is in local or global coordinates. You could then combine that with the cursor location.