As far as I can see the 3D drawings are limited to 16 * 16 .PNG premade download objects.
I have not used LibreOffice, and have been very familiar with AutoCad 10 years ago.
What I have to make is no more than lines in 3D such as one could in AutoCad > 11
or so, such as line m perpendicular to line l, give me the coordinates of their intersection.
Is that possible in LibreOffice ?