by Dan Peirce B.Sc.Also see printer3d.html
on http://www.openscad.org/ they say "OpenSCAD The Programmers Solid 3D CAD Modeller"
The forums linked here point out that units in OpenSCAD are arbitrary; however when the 3D model is put into the slicer program the numbers are interpreted as mm.
I found an existing 3D model of the Raspberry Pi.
This looks like the newest version of the board with the two positioning holes.
Some of the details are not present but it would not be hard to add them.
Since I am new to OpenSCAD it is not too surprising that when I look at the model I see things that I have not seen before but it is not hard to figure out what is happening. I see advantages in this method of creating a 3D model.
The OpenSCAD file used to generate the 3D opject is linked here support_astr1100_kpu.scad.
OpenSCAD does not contain native text ojects but it allows 2D DXF files to be imported and extruded to make a 2D drawing into a 3D object. I found a project that does this and can be imported to new projects.
This will work on different operating systems but the name should be changed to write.scad to get it working under Linux which is case sensitive on file names.
My OpenSCAD file is in a github repository. An explination of the project is also given.
This playlist seems to give a good introduction to OpenSCAD: