cascadio

cascadio

A Python library which uses OpenCASCADE to convert STEP files to a GLB file which can quickly be loaded by trimesh and other libraries.

The primary effort here is build and packaging using the wonderful work done recently on scikit-build-core and cibuildwheel. The goal is to produce wheels that don't require users to build OpenCASCADE themselves.

This is not intended to be a full binding of OpenCASCADE like OCP or PythonOCC. Rather it is intended to be an easy minimal way to load boundary representation files into a triangulated scene in Python. There are a few options for loading STEP geometry in the open-source ecosystem: GMSH, FreeCAD, etc. However nearly all of them use OpenCASCADE under the hood as it is pretty much the only open-source BREP kernel.

Install

The primary goal of this project is building wheels so vanilla pip can be used:

pip install cascadio

Currently this is building for non-MUSL flavors of manylinux, Windows x64, and MacOS x64+ARM. You can check PyPi for current platforms.

Motivation

A lot of analysis can be done on triangulated surface meshes that doesn't need the analytical surfaces from a STEP or BREP file.

Contributing

Developed on Linux which should build wheels locally with docker:

# this doesn't cache the OCCT build unfortunately.
# It would be nice if it did! You could do it by building OCCT
# in the manylinux images and then passing the new tag to CIBW
CIBW_BUILD="cp312-manylinux_x86_64" cibuildwheel --platform linux

Or, if you want to develop that will only work in your local environment for development:

# just run the `before-all` from pyproject.toml which is approximatly:
cd upstream/OCCT
cmake -G Ninja -DCMAKE_BUILD_TYPE=Release \
      -DUSE_RAPIDJSON:BOOL="ON" \
      -D3RDPARTY_RAPIDJSON_INCLUDE_DIR="../rapidjson/include" .
ninja
mv lin64/gcc/lib .

Then pip install . will build and install locally. Make sure to point LD_LIBRARY_PATH=upstream/OCCT/lin64/gcc/lib or wherever you put the libraries.

Future Work

Pull requests welcome!

• Add passable parameters for options included in the RWGLTF writer.
• use in-memory data for input and output, i.e. stepReader.ReadStream() instead of a file name. Ideally the Python function signature would be:
  • convert_to_glb(data: bytes, file_type: str, **parameters) -> bytes
  • Currently using file names because it's easier.
• Support IGES
  • Investigate using OpenCASCADE "Advanced Data Exchange" for Parasolid .x_b/.x_t and JT .jt support.