splinepy

splinepy is a python library for splines of arbitrary dimensions and degrees. The library supports Bezier, Rational Bezier, BSpline and NURBS with fast and easy-to-use APIs.

Install guide

splinepy wheels are available for python3.6+ for MacOS, Linux, and Windows:

pip install splinepy[all]  # including all optional dependencies
# or
pip install splinepy

Of course, you can install it directly from the source. In addition to the aforementioned compilers, this requires a cmake3.16+. If you don't have cmake, the easiest way to install it would be: pip install cmake.

git clone [email protected]:tataratat/splinepy.git
cd splinepy
git submodule update --init --recursive
python3 setup.py develop

Quick start

import splinepy
import numpy as np

# Initialize bspline with any array-like input
bspline = splinepy.BSpline(
    degrees=[2, 1],
    knot_vectors=[
        [0.0, 0.0, 0.0, 1.0, 1.0, 1.0],
        [0.0, 0.0, 1.0, 1.0],
    ],
    control_points=[
        [0.0, 0.0],  # [0, 0] (control grid index)
        [0.5, 0.0],  # [1, 0]
        [1.0, 0.0],  # [2, 0]
        [0.0, 1.0],  # [0, 1]
        [0.5, 1.0],  # [1, 1]
        [1.0, 1.0],  # [2, 1]
    ],
)

# We always store control points in 2D arrays with shape
# (total_number_of_control_points, physical_dimension).
# The indexing of the control grid is defined by iterating
# lower-indexed dimensions first. But if you prefer a
# grid-like structure, try
multi_index = bspline.multi_index
grid_cps = np.empty(bspline.control_points.shape)
grid_cps[multi_index[0, 0]] = [0.0, 0.0]
grid_cps[multi_index[1, 0]] = [0.5, 0.0]
grid_cps[multi_index[2, 0], 0] = 1.0
# which also supports ranges
grid_cps[multi_index[:, 0], 1] = 0.0
grid_cps[multi_index[:, 1], 1] = 1.0
grid_cps[multi_index[:, 1], 0] = [0.0, 0.5, 1.0]

assert np.allclose(bspline.control_points, grid_cps)

# Evaluate spline mapping.
# First, let's form parametric coordinate queries
queries = [
    [0.1, 0.2],  # first query
    [0.4, 0.5],  # second query
    [0.1156, 0.9091],  # third query
]
physical_coords = bspline.evaluate(queries)

# we can also execute this in parallel using multithread
# executions on c++ side (for heavy multi-queries scenarios)
physical_coords_parallel = bspline.evaluate(queries, nthreads=2)

# this holds
assert np.allclose(physical_coords, physical_coords_parallel)

You can also try splinepy online by clicking the Binder badge above!

Feature Summary

For details, please take a look at the documentation. Most of the functions are vectorized and capable of multithread executions.

Splines

Any type of spline is capable of:

• computing spline mappings, derivatives, partial derivatives, jacobian, basis functions, basis function derivatives, basis function partial derivatives, and proximity (point inversion, nearest mapping search),
• degree elevation,
• extracting boundary splines, and
• visualization (see visualizing with splinepy).

In addition to the common features, Bezier and Rational Bezier can:

• add/multiply two splines,
• split itself into multiple patches,
• create derivative splines, and
• compose an inner spline into an outer spline and compute its composition derivative

and BSpline and NURBS can:

• reduce degrees,
• insert and remove knots, and
• extract bezier patches.

Some BSpline fitting routines from The NURBS Book:

• curve interpolation/approximation
• surface interpolation/approximation

Multipatch

Splinepy offers a common interface for multipatch geometries, i.e., geometries consisting of multiple, individual splines of arbitrary types. This concept is used for complex geometries and for Isogeometric Analysis. Multipatch objects have the following functionalities:

• determine patch-interfaces automatically
• identification of boundary faces
• boundary assignment using different techniques, relying either on the boundary position or on the continuity in between patches
• Boundary extraction

IO

Available in splinepy.io.

Formats	Description
iges	Loads/Exports splines from an IGES file
irit	IRIT compatible format
json	(Custom) easy-to-read format, supports base64 encoding
mfem	MFEM compatible .mesh format. Supports structured multi-patch splines in controlpoints_cartesian and 2D single-patch splines
gismo	GISMO compatible .xml format
npz	Based on np.savez()
xml	RWTH CATS spline format

Dependencies

The following are direct dependencies for splinepy. Please feel free to check out the repositories linked.

Package	Description	Python	C++
pybind11	Binds c++ and python	X	X
SplineLib	Main functionalities for BSplines and NURBS		X
bezman	Main functionalities for Beziers and rational Beziers		X
napf	Creates k-d trees that provide initial guess for proximity search. Wraps nanoflann		X
numpy	Fast array data storage and manipulation	X
gustaf	Conversion to mesh representation, visualization, and helpers	X
scipy	(Optional) Creates sparse matrices, where applicable	X
cmake	Platform independent build system for c++ implementations		X
setuptools	Build python package	X
wheel	Implementation of python binary packaging standard	X	X
cibuildwheel	Builds and tests wheels on CI server	X	X