occ_gordon: A Curve Network Interpolation Library for OpenCASCADE (OCCT)

occ_gordon is a lightweight C++ and Python library that implements curve network interpolation using B-spline surfaces within the OpenCASCADE (OCCT) framework.

OCCT lacks built-in support for Gordon surface interpolation, which is a method for interpolating arbitrary large curve networks. This library was developed to provide that functionality and help create smooth, accurate surfaces from interconnected curves in OCCT.

What is a Curve Network?

A curve network is a collection of interconnected curves that define the structural framework or "skeleton" of a surface or shape. By interpolating a curve network, complex surfaces can be created accurately.

Key Features ⭐

• ✨ Gordon Surface Interpolation: Implements the Gordon surface interpolation method, a generalization of the Coons patch, for smooth B-spline surfaces from profile and guide curves.
• 🔧 Curve Network Reparametrization: Reparametrizes the curve network if needed to improve interpolation robustness.
• 📦 Single Header Distribution: A generated standalone header is available for packaging and release workflows.
• 🤝 OpenCASCADE Integration: Fully integrated with OpenCASCADE for OCCT-based projects.
• 🐍 Python Support: Python bindings are available for use with pythonocc.
• 🚀 Lightweight: Based on a streamlined version of the TiGL library, focused on curve network interpolation using B-splines and no additional runtime dependencies besides OCCT.
• 🔒 Open Source and Apache Licensed: Released under the permissive Apache 2.0 license.

About the Gordon Surface Method

The Gordon surface interpolation method was first published by W.J. Gordon in 1969. It enables surface generation from an arbitrary number of guide and profile curves using B-splines. It extends the Coons patch method to more complex curve networks.

Usage Example (C++)

For the normal library build, include the standard header:

#include <occ_gordon/occ_gordon.h>

The main function for curve network interpolation is occ_gordon::interpolate_curve_network.

#include <occ_gordon/occ_gordon.h>

std::vector<Handle(Geom_Curve)> vcurves, ucurves;

// Create the curve network
...

double inters_tol = 1e-4; // distance, in which the curves need to intersect

auto surface = occ_gordon::interpolate_curve_network(ucurves, vcurves, inters_tol);

Single Header Distribution

If you want a single-header deployment, download the generated occ_gordon_single.hpp artifact from the GitHub Actions build workflow or from a published release asset.

Use it like this:

#include <occ_gordon_single.hpp>

This form is intended for packaging and redistribution. The generated header does not need to be committed to the repository.

If you need to generate the header locally, enable the optional CMake switch described in the build section below.

Use from Python

To install occ_gordon from Python, install it via conda/mamba from conda-forge:

conda install occ-gordon -c conda-forge

To use it, pass two curve arrays to the function:

from occ_gordon import interpolate_curve_network

...
surface = interpolate_curve_network(profile_curves, guide_curves, tolerance=1.e-5)

Building

To build occ_gordon, you need a recent version of CMake (3.15 or higher) and a working installation of OpenCASCADE.

cmake -S . -B build -DOpenCASCADE_DIR=<path/to/cmake/opencascade> -DCMAKE_INSTALL_PREFIX=<path/to/install>
cmake --build build
cmake --build build --target install

To build the optional single-header release artifact as part of the build, add:

cmake -S . -B build -DOpenCASCADE_DIR=<path/to/cmake/opencascade> -DCMAKE_INSTALL_PREFIX=<path/to/install> -DOCC_GORDON_BUILD_SINGLE_HEADER=ON

That keeps the normal library build unchanged and only enables Python when you explicitly request the generated header.

License

occ_gordon is licensed under the Apache 2.0 License, making it free to use, modify, and distribute in personal and commercial projects.

Citing

This algorithm was originally developed as part of the TiGL library. If you use the occ_gordon library in your work, please cite the following paper:

Siggel M. et. al. (2019), TiGL: An Open Source Computational Geometry Library for Parametric Aircraft Design

@article{siggel2019tigl,
	title={TiGL: an open source computational geometry library for parametric aircraft design},
	author={Siggel, Martin and Kleinert, Jan and Stollenwerk, Tobias and Maierl, Reinhold},
	journal={Mathematics in Computer Science},
	volume={13},
	number={3},
	pages={367--389},
	year={2019},
	publisher={Springer},
    doi={10.1007/s11786-019-00401-y}
}