pyvista-cad 0.0.2

PyVista accessor and reader-registry plugin for CAD formats (STEP, IGES, BREP, DXF, 3MF, IFC, FCStd) and bridges to build123d, cadquery, OCP, and gmsh.

pyvista-cad

CAD format reading, writing, and CAD-style plotting for PyVista.

pyvista-cad adds CAD-format support to PyVista: STEP, IGES, BREP, DXF, 3MF, IFC, FreeCAD .fcstd, OpenSCAD .scad, and glTF. It registers a .cad accessor on every pv.DataSet / pv.MultiBlock and wires reader entries into pv.read(...). It also adds CAD-style rendering: smoothly shaded faces with the model's topological B-rep edges instead of triangle-mesh noise, via .cad.plot() and a plotter.cad component. No monkey-patching, no forks, no direct VTK calls.

Install matrix

Extra	Adds	Formats unlocked
(base)	ezdxf	DXF read + write, glTF read + write
[step]	build123d, cadquery-ocp	STEP, BREP, FCStd, build123d bridge
[step-light]	cascadio	STEP (read-only, faster, no colors)
[3mf]	lib3mf	3MF read + write
[ifc]	ifcopenshell	IFC read (with property sets)
[iges]	pyiges[full]	IGES read
[gmsh]	gmsh	gmsh bridge for FEA meshing
[openscad]	(uses openscad CLI)	SCAD read
[full]	all of the above	every supported format

Python support: 3.10 – 3.13. Python 3.14 is not yet supported: the [step]/[full] extras depend on cadquery-ocp, which publishes no cp314 wheels for any platform. 3.14 will be added once those wheels ship.

trimesh interop is provided by pyvista core (pyvista.from_trimesh, pyvista.to_trimesh) and the pyvista-trimesh package's .trimesh accessor (install pyvista-cad[trimesh]); pyvista-cad does not duplicate it.

pip install pyvista-cad           # DXF and glTF only
pip install pyvista-cad[step]     # add STEP, BREP, FCStd
pip install pyvista-cad[full]     # everything

Quick start

import pyvista as pv
import pyvista_cad  # registers the .cad accessor and reader entries

mesh = pv.read('part.step')              # MultiBlock of parts with cad.color, cad.label
mesh.plot(show_edges=True)

floorplan = pv.read('floor.dxf')         # PolyData with Layer cell data
layers = floorplan.cad.split_by_layer()  # MultiBlock keyed on layer

CAD-friendly plotting

A generic mesh viewer draws the triangulation. With show_edges=True you see every facet edge, an artifact of the tessellation tolerance. A CAD application instead shows smoothly shaded faces with the model's topological edges (the B-rep feature curves) on top. pyvista-cad reproduces that: analytic surface normals so a coarse mesh still shades round, topological edges recovered from the cached B-rep, triangle edges hidden.

import pyvista as pv
import pyvista_cad
from pyvista_cad.examples import downloads

mb = pyvista_cad.read_step(downloads.step_part_path())  # NIST AM Bench specimen

mb.cad.plot()                       # shaded faces + topological edges

# Or compose it into a scene, color faces by a scalar, keep the edges:
part = mb[0]                        # a cached block keeps its B-rep
part['height'] = part.points[:, 2]
pl = pv.Plotter()
pl.cad.add(part, scalars='height', cmap='viridis')
pl.show()

.cad.plot() and the plotter.cad component accept a MultiBlock, PolyData, raw TopoDS, or a build123d / cadquery object; a plain mesh with no B-rep origin degrades to crease feature edges.

Real-world workflow

Load a STEP assembly, locate a part, drive it through gmsh to a tetrahedral FEA mesh, then clip to expose the interior. Needs the [gmsh] extra.

import gmsh
import pyvista as pv
import pyvista_cad
from pyvista_cad.examples import downloads

assembly = pv.read(downloads.step_assembly_path())  # 3-part NIST build assembly
print(assembly.cad.assembly_tree())                 # nested dict of block names
matches = assembly.cad.find('*PartCAD')             # glob -> list of (path, block)
path, part = matches[0]

gmsh.initialize()
try:
    gmsh.model.occ.importShapes(downloads.step_part_path())
    gmsh.model.occ.synchronize()
    gmsh.option.setNumber('Mesh.MeshSizeMax', 2.0)
    gmsh.model.mesh.generate(3)
    grid = pyvista_cad.from_gmsh()
finally:
    gmsh.finalize()

grid = grid.extract_cells(grid.celltypes == 10)     # keep VTK_TETRA
clip = grid.clip(normal='x', crinkle=True)
clip.save('part_tets.vtu')                           # full tet mesh round-trips

The Quick start uses bundled offline fixtures (bracket_step_path(), a parametric L-bracket committed as STEP; drawing_dxf_path(), a layered 2D drawing). The other examples pull real, openly licensed parts from pyvista_cad.examples.downloads (cached on first fetch) — the NIST AM Bench LPBF specimen and its 3-part build assembly.

Common tasks

Task	How
Read a STEP assembly with per-part colors	pv.read('a.step') returns a MultiBlock; each block has cad.color and cad.label
Split a DXF by layer	pv.read('a.dxf').cad.split_by_layer()
Round-trip a 3MF print	pyvista_cad.write_three_mf(mb, 'b.3mf') (object color + units kept)
Load an IFC building and filter walls	mb = pv.read('b.ifc'); walls = mb.cad.find(ifc_type='IfcWall')
Read IFC property sets	json.loads(block.field_data['cad.psets'][0]) returns the source Pset_* / Qto_* dict
Convert build123d to PyVista	pyvista_cad.from_build123d(part) (preserves color, label, transform)
Mesh a STEP for FEA in gmsh	pyvista_cad.to_gmsh(...) then gmsh; see examples/05_workflows/cad_to_fea_tet_mesh.py
Generate a signed distance field from CAD	see examples/05_workflows/cad_to_signed_distance.py

Fidelity and limitations

Round-trip fidelity varies by format. Tessellated formats (STEP, IGES, BREP, FCStd) discretize analytic surfaces on read; the originating B-rep is cached so tessellate() can refine it. DXF and 3MF round-trip geometry and metadata within documented tolerances. IGES and SCAD are read-only.