PRC (Product Representation Compact) is the 3D format standardised as ISO 14739-1 and used, alongside U3D, inside 3D PDFs. Where U3D only carries triangles, PRC can carry a product structure, exact B-Rep surfaces, saved tessellation, colours and product manufacturing information. CAD publishing tools and LaTeX packages such as media9 and Asymptote write it. You usually see a standalone .prc file when a tool exports the stream on its own or when someone extracts it from a PDF.
You can open a .prc file in the CADProps workspace. It reads the product tree, shows the saved triangles and rebuilds supported B-Rep faces as a mesh, with each part's transform and colour. You can rotate and section the model, hide parts, check the bounding box, measure point-to-point distances and export STL, OBJ, GLB, glTF, 3MF or mesh STEP after sign-in. CADProps reads standalone PRC files only; a PDF upload is treated as a drawing, and its embedded 3D content is not opened.
What is inside a PRC file
A PRC file is split into compressed sections: a product tree of occurrences and parts, a tessellation section with triangles, a topology section with B-Rep bodies, and global sections for colours, materials and units. A single file can hold both forms of a part. Publishing tools often keep the tessellation for display and add the B-Rep so a reader can measure exact edges.
PRC also defines a highly compressed tessellation that stores triangles as a compact list of positions and normals. Many 3D PDF exports from engineering tools use it.
What is shown and what is left out
- Saved triangles, including the supported highly compressed meshes, with the part structure, transforms and base colours. Normals are recalculated for shading.
- B-Rep faces without a saved tessellation are rebuilt as a mesh when their surfaces are supported. Faces that cannot be rebuilt are left out, and the model is marked incomplete.
- PMI, textures, vertex colours, views, wires and point clouds are skipped.
- Some compressed meshes use encodings that are not yet decoded. Very large files can also hit the processing time limit. In both cases the parts that could not be read are listed in the warning, or the file fails with a message saying why.
Even when a PRC file contains exact B-Rep, the view is an approximate mesh and exact STEP export is not available. A mesh STEP made from it contains triangles; see what B-Rep is and tessellation for the difference.
Units and measurements
PRC files can declare a length unit for the model and for each product. CADProps reads that declaration and converts to millimetres, so the scale is marked verified. If the file gives no reliable unit, millimetres are assumed, and area, volume and mass are turned off.
A declared unit only says what the numbers mean, not that the model was drawn at real size. Scientific figures in 3D PDFs often use normalised or arbitrary coordinates, so a skull model can come out two millimetres long. Measure a feature whose real size you know before quoting a dimension; the scale factor guide shows how to spot a wrong factor. For manufacturing work, ask for the source CAD file or a STEP export. The format matrix lists every input and its limits.
Original article: CADProps · https://www.cadprops.com/guides/open-prc-file-online/