3D preview of SOLIDWORKS parts and assemblies

2026-11-07

Question

Can TeamCraft show native SOLIDWORKS parts (.sldprt) and assemblies (.sldasm) in the 3D viewer without SOLIDWORKS, eDrawings or a translation service, and with the same quality as the NX preview (3D preview of NX parts)?

Findings

Files from SOLIDWORKS 2015 on are a sequence of Deflate sections (see src/swpart.rs). Three of them answer the question.

Parts: the display tessellation

• Contents/DisplayLists holds the tessellation SOLIDWORKS draws the part with, serialised as an MFC archive (class definitions ff ff 01 00, class tags with bit 15 set).
  • One uoTempBodyTessData_c per body, each followed by its uoTempFaceTessData_c faces.
  • Each face is a set of plain triangle strips. There is no index buffer; the triangle order is the usual strip order, counter-clockwise around the outward normals.
  • Each face carries three typed arrays, each with a header of element size, type (8 = integer, 100 = float), 2, count:
    • the strip lengths (u32);
    • the vertices (f32 xyz, metres);
    • a unit surface normal per vertex (f32 xyz).
  • The face header is n_triangles, n_strips (SOLIDWORKS 2016/2018); 2024 adds 32 bytes. Holes with a shaded cosmetic thread hold a second mesh on the same cylinder, recognisable because it has no face header; it is skipped.
• Tested files:
  • 57 parts decoded completely, 470 000 triangles: 47 parts of a real gearbox project (SOLIDWORKS 2024) and the 10 NIST parts in tests/fixtures/cad (2016 and 2018).
  • The NIST parts agree with their STEP and SAT exports: ctc-01 has an identical bounding box, ftc-11 is within 0.03 mm (chords of a 31.5 mm radius).
• Watertight:
  • Neighbouring faces do not share vertices, so positions are welded (1 µm). After that 45 of 47 parts are closed.
  • The rest have micrometre cracks where two faces sample their common edge differently (T-junctions, helical gear flanks). These are invisible in the viewer.
• Fineness: the resolution is the document’s image quality setting, about 15° between neighbouring normals (≈ 24 facets around a cylinder), much like the NX lightweight data. Because every vertex carries the exact surface normal, the same PN-triangle refinement as for NX applies. On NIST ftc-11 against the analytic surfaces the deviation drops from 0.034 mm to 0.004 mm (95 % of the points).

Assemblies: placements in the component tree

• swXmlContents/COMPINSTANCETREE (already read for file references) contains:
  • one swReference per component instance, with swTransform: 16 numbers r00 r01 r02 0 r10 r11 r12 0 r20 r21 r22 0 tx ty tz 1. A point lands at p · R + t (row vectors, t in metres), the same convention as NX;
  • the flags swSuppressed and swHidden;
  • the referenced model, and through it the file (swFile swPath, the author’s absolute path, so components are found by file name).
• Sub-assemblies are models with their own swReference children, placed relative to the sub-assembly. Each configuration of the assembly has its own top model; swMostRecentConfiguration="YES" marks the one that was active when the file was saved.
• Checked against NIST: the NIST MTC assembly gives the same 36 instances as its NX version. The positions agree with the NX placements (themselves verified against a JT export) within 0.025 mm after one global shift of the origin.
• Checked on the gearbox: a real gearbox assembly lists 128 instances, including two levels of sub-assemblies. Its placed part boxes fill the assembly’s stored bounding box exactly.
• Suppressed components keep their transform and are always marked hidden too. swHidden reflects the display state that was active when the file was saved.
• Newer assemblies (format 16000 and up) also store copies of their parts’ meshes (FaceTessellations/*, same face records, part coordinates). Older ones copy the parts’ display lists into their own. Composing from the part files, as for NX, works for both and stays current when a part changes.

The exact geometry

• Contents/Config-N-Partition is a zlib-wrapped Parasolid transmit file: neutral binary, schema 13006 plus embedded deltas. A test reader parsed all 55 part streams and matched the NIST STEP exports to 1e-15 m.
• A full tessellation of it would be possible: planes, cylinders, cones, tori, spheres, rational B-surfaces, swept surfaces and rolling-ball blends all occur. With truck that is weeks of work, mainly for the blends and the tolerant edges.
• The display tessellation with PN refinement is good enough for a preview, so the exact geometry is not needed now.

Licences and law

• No SOLIDWORKS software or SDK was used, and nothing was decompiled. The layout was found by analysing files, which EU law permits for interoperability (Directive 2009/24/EC Art. 6, UrhG §69e).
• “SOLIDWORKS” and “Parasolid” are trademarks of Dassault Systèmes and Siemens; they are named only to say which files are read.
• The files of the gearbox project used for testing are not part of the repository. The tests use the openly licensed NIST files only.

Decision

• solidworks-part: read Contents/DisplayLists, weld the positions (1 µm) and refine with PN triangles like NX (mesh/sw.rs).
• solidworks-assembly: compose the preview from the part files found by name, with the placements and the hidden or suppressed flags of the component tree. This is the same pipeline as NX assemblies (services/assemblies.rs).
• The thumbnails of SOLIDWORKS parts and assemblies are rendered from the 3D preview instead of the stored PreviewPNG. An assembly none of whose parts are in TeamCraft keeps the stored image.
• Not covered:
  • files before 2015 (OLE compound files);
  • virtual components (their geometry lives inside the assembly);
  • the active display state, if it differs from the saved swHidden;
  • the Parasolid geometry.