3D preview of Creo assemblies

2026-11-12. Findings from reading the files only – no PTC software, no toolkit, nothing decompiled.

Question

Can TeamCraft put together the 3D preview of a PTC Creo assembly (name.asm.N) from the previews of its parts, as it does for NX, SOLIDWORKS, Inventor and CATIA? What does an assembly store about its components, and in which unit?

Samples

No openly licensed Creo assembly was found (search of 2026-11-08: NIST, GitHub, Zenodo, GrabCAD, PTC tutorials, open hardware). The format was decoded on two public GitHub projects without a licence, which are therefore used locally only and never committed:

a model rocket (rocket.asm.1: three parts, millimetres, Creo 3);
a scissor jack (sc9132-2000-1.asm.1: three sub-assemblies, 27 part instances, skeleton models, family-table generics, inches, Creo 7).

The repository tests build synthetic assemblies around the NIST part ctc-01 (see Tests) until real assemblies can be added.

Findings

An assembly uses the part container (#UGC:2 ASSEMBLY … header, text table of contents, LZW sections) and the same tagged format (3D preview of Creo parts). Its own VisibGeom holds only assembly-level datums – the geometry is in the part files.
Section NeuAsmSld (struct neut_assem) lists the direct components in members, one struct each:
```
id = 42  type = 2  name = 'MS_MID'  family_name = 'MS_MID'
e1 = [1, 0, 0]  e2 = [0, -0.995, 0.096]  e3 = [0, -0.096, -0.995]
origin = [34.58, 0, 0]
```
- type 2 is a part (name.prt.N), 1 an assembly (name.asm.N, including skeleton assemblies); other types are not seen.
- e1, e2, e3 are the images of the component’s x, y and z axes in the parent’s frame and origin its origin: a component point p lands at origin + p.x·e1 + p.y·e2 + p.z·e3 – the row convention of nxasm::Component (rotation = [e1, e2, e3]). The other reading (transposed) puts the rocket’s base cone the wrong way round; the composed models match the stored thumbnails.
- Only direct children are listed: a sub-assembly is its own file, read the same way, its placements composed with the parent’s.
- name is the model name in upper case without extension; a family-table instance is listed under the generic’s name (SC9132-2010-X_GENERIC), whose file the instance’s geometry comes from.
- The same placements appear in FeatDefsCmp (place_rec_ptr.local_sys, trf_arr.transf) with the component’s model_ptr; MdlRefInfo holds the referenced models of each placement constraint. NeuAsmSld is enough for the preview.
Units are in section ND:0:UnitSystemDef_L03:1, an object archive parsed by the same tagged reader: string_xar holds the names in order of first use, and the length unit’s name is the string after Offset (mm, in, …, with its definition after it: 0.001000 m, 1.000000 in). double_xar[0] is the length scale in metres for non-metric systems (0.0254). Parts carry the same section: the NIST part ctc-05 is in inches (its STEP export too), ctc-01 in mm. Parts and placements are converted to millimetres, so components in different units fit together.
File names: TeamCraft stores Creo files without the iteration suffix (bracket.prt.7 → bracket.prt, cadformat::creo_iteration), so a component is found as <name>.prt or <name>.asm (lower case), like SOLIDWORKS and Inventor components (services::assemblies).

Part reader: parts without a starting face

The parametrisation conventions of a part’s faces are resolved by propagation from planes with the identity frame (and freeform faces) – 3D preview of Creo parts. Turned parts often have none (all planes are perpendicular to an off-axis axis): every face then kept the default convention and the mesh fell apart (rocket nose: 102 open edges). When a part has no starting face at all, one face (planes first, then cylinders, cones, tori) is now tried with each candidate convention; the propagation that makes the most edge samples coincide is kept, the default convention only loses when another candidate is strictly better. The rocket’s body became closed, its nose went from 102 to 9 open edges. Parts with a starting face are unchanged: seeding their unreached faces as well made two NIST parts worse.

Gaps

Family-table instances are shown with the generic’s geometry.
Suppressed or excluded components, simplified representations and explode states are not evaluated (NeuAsmSld lists the members of the master representation).
The sample parts from older Creo versions show part-reader gaps: some faces arrive as stubs without data (rocket nose: 2 of 12 faces), and several scissor-jack parts keep open edges or single wrong faces.
No real assembly is a repository fixture yet.

Tests

Unit tests encode small sections in the tagged format (a writer that spells out every transition) and check the members, the placement convention, units and damaged input. A synthetic assembly placing the NIST part ctc-01 twice (one sub-assembly, rotated, in inches) checks the composition end to end.

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