geomcore

A pure, standalone geometric kernel for CAD-grade curves and surfaces — parametric evaluation, rigid transformations, and analytic curve-on-surface parametrization, built as small, independently useful Rust libraries with a clean API and idiomatic Python bindings.

geomcore is not a modeling/CAD system — no topology, no B-rep, no boolean operations (yet). It's the layer underneath one: parametric curve/surface evaluation, rigid transformations, and curve-on-surface parametrization, usable on their own by anyone who needs robust computational geometry — not just future CAD-kernel builders.

Status

Proof-of-concept. Implemented so far:

• Parametric evaluation for lines, circles, ellipses, parabolas, hyperbolas, and B-spline curves in 3D (plus 2D lines and circles, the shapes curve-on-surface parametrization produces).
• Parametric evaluation for planes, cylinders, cones, spheres, tori, and B-spline surfaces.
• Rigid transformations (translation, rotation, mirroring, scaling) via a single Transform type.
• Analytic curve-on-surface parametrization for lines and circles on the five elementary surfaces (plane, cylinder, cone, sphere, torus).

Not implemented yet: curve/surface intersection, extrema computation, topology/B-rep, and a numeric-approximation fallback for curve-on-surface parametrization when no closed form exists.

Evaluation results are validated against golden fixtures with CAD-kernel-grade tolerances (1e-7).

See ROADMAP.md for what's coming next and CHANGELOG.md for release history.

Rust

use geomcore::{Point3, Vector3};
use geomcore::curves::Circle3D;

let circle = Circle3D::new(Point3::ORIGIN, Vector3::Z, 2.0).unwrap();
let point = circle.eval_point(std::f64::consts::PI / 4.0);

cargo add geomcore

Not yet published to crates.io — coming with the first release.

Python

from geomcore import Point3, Vector3
from geomcore.curves import Circle3D
import math

circle = Circle3D.new(Point3.origin(), Vector3.z(), 2.0)
point = circle.eval_point(math.pi / 4)

pip install geomcore

Not yet published to PyPI — coming with the first release.

Why

Most of what a CAD kernel needs — parametric evaluation, transformations, curve-on-surface math — is useful on its own, to anyone doing computational geometry, not just people building a full modeling system. geomcore grows these as small, independently useful, well-tested libraries, with the goal of eventually adding up to a complete, open, high-performance CAD kernel — without forcing that scope on anyone who just needs the math.

Acknowledgments

Some algorithms in this library were written using modules of Open CASCADE Technology (OCCT) as a reference.

License

Dual-licensed under MIT or Apache-2.0, at your option.

Contributing

New curve/surface types can be added by implementing ParametricCurve3D/ ParametricSurface without touching the core crate's dispatch code — see the crate docs for details.