gtsam-nb: nanobind bindings for GTSAM

This repository provides Python bindings for GTSAM using nanobind.

Most of the code, tests, data, etc. are originally from the official GTSAM repository, just slightly modified to work with nanobind and clean up python typing.

Installation

It's all available via pip!

pip install gtsam-nb  # if using pip
uv add gtsam-nb       # if using uv

Then use as you would the official gtsam Python bindings:

import gtsam

gtsam-nb should be a near drop-in replacement for the official gtsam python package, with the following (mostly minor) exceptions:

• Unlike pybind11, nanobind doesn't accept python lists in place of numpy arrays for function arguments. So wrapping lists in np.array(...) is necessary.
• OrderingType enum values are now accessed as gtsam.OrderingType.XXX instead of gtsam.Ordering.OrderingType.XXX.
• lambda_ is now lambda_a in gtsam.LevenbergMarquardtOptimizer due to how nanobind handles private methods.
• [FEAT] NonlinearFactorGraph and Values interface more like a python list and dict, respectively including constructors and [] usage.

There are likely other tweaks required (please let us know if you find any), but they should all be fairly minor.

Why?

There's a handful of reasons why I decided to make this (most of which should hopefully be resolved when gtsam 4.3 is released):

• As of the writing of this README, gtsam's most recent python release only supports up to python 3.11. This has restricted the python version for a number of my projects.
• In addition, the current stable gtsam on pypi are incompatible with numpy>=2.0.
• The gtsam python bindings don't include type stubs, making development in an IDE and type checking more difficult.
• A switch to nanobind over pybind11 for a number of reasons, including
  • nanobind results in faster compilation, smaller binaries, and a smaller overhead. See benchmarks for more details.
  • nanobind has built-in stub generation, make setting up type stubs a cakewalk.
  • Based on my knowledge, nanobind has a more permissive ABI compatibility story than pybind11, which makes it easier to extend gtsam with custom C++ code that will just work together. See here and here.
  • Since all my projects now use nanobind, if I want to add new C++ factors to GTSAM from python, I need nanobind bindings.
• I often have found the gtsam bindings to be missing a method or two that I need. This then requires me to build the bindings from source. By having my own version, I can easily add in any missing methods I need, and get them merged and released on PyPI quickly. This is more difficult for the official gtsam bindings since they are released alongside GTSAM itself.

Hopefully in the future these issues will be resolved in the official gtsam bindings, and this repository will no longer be necessary. But for now, this is a useful stopgap.

Building

Building is all piped through scikit-build-core (which we use behind uv). The only dependency is GTSAM 4.2, which will be resolved in the following order:

1. If vcpkg.sh was ran to clone vcpkg into the .vcpkg folder, then GTSAM will be built and installed via vcpkg.
2. If not, GTSAM is searched for in the system paths.
3. If not found, GTSAM will be cloned and built from source in the build process.

To actually perform the building from source, clone the repository and run:

pip install -e .   # if using pip
uv sync --verbose  # if using uv

This will build the C++ extension and install the package in editable mode in whatever environment you have activated.

Contributing

There is likely a hidden bug or two, and definitely still some missing methods. Please feel free to open issues or PRs! I imagine most PRs will be to add missing methods or classes from GTSAM so they can be merged and released quickly (especially since it's all automated through our CI setup).