The rdsupdate command allows new versions of parts to be sustituted into an
existing 3D model.  I find this is very helpful since I generally build the
model using the "draft" parts (which are simpler and render quicker), then
update to the "final" parts (more detailed, but slower) for final rendering.

The usage is pretty simple...

rdsupdate [-v] [-Pparts_dir] source output

-v : runs in verbose mode
-P : specify a parts directory to use for substitution

So if the final version of the parts were in "Onyx:Home:Lego3d:Parts-Final",
and your draft model was called Model.draft, you could use the following
command to create a final model:

rdsupdate -v "-POnyx:Home:Lego3d:Parts-Final" Model.draft Model.final
