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NURBS Sharp

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NURBS Sharp is a small, dependency-free NURBS (Non-Uniform Rational B-Spline) library for .NET. It provides data structures, evaluators, topology operators, I/O and tessellation utilities implemented using only the .NET standard library.

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Table of Contents

Features

  • Generation and evaluation of NURBS curves, surfaces
  • Topology operators: degree elevation/reduction, knot insertion/removal/refinement, join/split
  • Generation capabilities: interpolation, least squares approximation, primitive shapes
  • Intersection calculations: Ray-Box, Ray-Mesh, Curve-Curve, Curve-Surface, Surface-Surface, Surface-Plane
  • IO helpers:
    • Mesh only: OBJ/STL export, simple BMP export
    • NURBS only: IGES import/export (Point, Curve, Surface entities supported)
  • Tessellation utilities for curves and surfaces
  • Targets: .NET 8 and .NET Standard 2.1

Limitations

  • Viewer: This library does not include a 3D model viewer. To inspect model details, a 3D rendering library or file export is required.
  • NURBS Surface: TrimSurface is not yet implemented.
  • Knot Vector: Currently, only "Clamped" knot vectors are supported (multiplicity = degree + 1).
  • IGES Support:
    • Import: Only supports Entity Type 126 (Rational B-spline curve), and 128 (Rational B-spline surface).
    • Export: Only supports Point and NURBS entities. Mesh export is not supported.
  • Mesh Export (OBJ/STL): Only supports Mesh objects. Direct export from NURBS is not supported (tessellation required).
  • Intersection Calculations:
    • The current state may be unstable due to its dependence on initial conditions.

Installation

Install via NuGet:

dotnet add package NurbsSharp

Or add the package reference to your project file.

Quick Start

Basic usage (C#):

using NurbsSharp.Core;
using NurbsSharp.Geometry;
using NurbsSharp.Tesselation;
using NurbsSharp.IO;

// Create a NURBS surface and evaluate a point
int degreeU = 3, degreeV = 3;
var knotsU = new double[] {0,0,0,0,1,1,1,1};
var knotsV = new double[] {0,0,0,0,1,1,1,1};
var kvU = new KnotVector(knotsU);
var kvV = new KnotVector(knotsV);

// Build control points (u x v grid)
ControlPoint[][] controlPoints = new ControlPoint[4][];
controlPoints[0] = new ControlPoint[] {
    new ControlPoint(0.0, 0.0, 0.0, 1),
    new ControlPoint(1.0, 0.0, 1.0, 1),
    new ControlPoint(2.0, 0.0, 3.0, 1),
    new ControlPoint(3.0, 0.0, 3.0, 1)
};
// ... Create Control Points ...

var surface = new NurbsSurface(degreeU, degreeV, kvU, kvV, controlPoints);
var point = surface.GetPos(0.5, 0.5);
Console.WriteLine(point);

Examples

tessellate a surface and export to STL:

int divideN = 20;
var mesh = SurfaceTessellator.Tessellate(surface, divideN, divideN);
using (var fs = new FileStream("test_output.stl", FileMode.Create, FileAccess.Write))
{
    await STLExporter.ExportAsync(mesh, fs);
}

Examples Project: https://github.com/nyarurato/NurbsSharpSample
Github Wiki: https://github.com/nyarurato/NurbsSharp/wiki/Samples

Documentation

API Docs: https://nyarurato.github.io/NurbsSharp/

Development

Clone the repo and build locally:

dotnet restore
dotnet build -c Debug

Run unit tests:

dotnet test -c Debug

Project layout highlights:

  • src/Core — numeric helpers and core types (BoundingBox, Ray, KnotVector, LinAlg, etc.)
  • src/Geometry — NurbsCurve, NurbsSurface, NurbsVolume, Mesh, etc.
  • src/Evaluation — evaluators (curve/surface/volume)
  • src/Operation — topology operators (degree, knot, join, split, surface operators)
  • src/Generation — interpolation, least squares approximation, primitive shape generation
  • src/Intersection — intersection calculations (Ray-Box, Ray-Mesh, Curve-Curve, Curve-Surface, BVH structures)
  • src/IO — OBJExporter, STLExporter, BMPExporter, IGES import/export
  • src/Tesselation — tessellation (curve/surface)

Contributing

Contributions are welcome. Typical workflow:

  1. Fork the repository
  2. Create a branch with a descriptive name
  3. Add tests for new behavior where appropriate
  4. Open a pull request against master

License

MIT License

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