Convert only part of a model

Real engineering assemblies contain far more than you want to simulate — the mounting frame, the trolley it sits on, sometimes the building. Converting all of it wastes time and fills your geometry with volumes no particle will ever reach, so the converter offers two independent ways of cutting a model down. They combine freely.

Selecting by name

The first is by name. --include-name and --exclude-name take regular expressions matched against the part name stored in the CAD file, case-insensitively, and either may be repeated. Matching an assembly takes its whole subtree along with it, which is usually what you want:

--include-name 'Bucket' --exclude-name '^SOLID\b'

Add --name-filter-case-sensitive if you need the matching to respect case.

Selecting by region

The second is geometric. --clip-box restricts the conversion to an axis-aligned box, given as xmin ymin zmin xmax ymax zmax in the assembly's global frame. Note that these are STEP file units, before the conversion to centimetres — so if your file is in millimetres, so is your clip box:

--clip-box -50 -50 -20 50 50 20

Every solid is then classified against that box before any meshing happens. Solids fully outside are dropped; solids fully inside are kept unchanged; and solids straddling the boundary are cut against it with a boolean intersection, so only the part inside survives. Assemblies left with no surviving children disappear from the output tree altogether.

By default, subtrees that end up entirely inside the box keep their shared logical definitions, which keeps the output compact when a part is repeated many times. If you need one distinct volume per surviving occurrence instead — say because you want to name them individually later — pass --clip-deduplicate none.