https://github.com/blazej-bucha/charm
C/Python library to work with spherical harmonics up to almost arbitrarily high degrees
https://github.com/blazej-bucha/charm
c-language geodesy geoscience gravity-field python spherical-harmonics topography
Last synced: 6 months ago
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C/Python library to work with spherical harmonics up to almost arbitrarily high degrees
- Host: GitHub
- URL: https://github.com/blazej-bucha/charm
- Owner: blazej-bucha
- License: bsd-3-clause
- Created: 2022-05-16T06:10:27.000Z (over 3 years ago)
- Default Branch: master
- Last Pushed: 2025-04-07T07:26:51.000Z (6 months ago)
- Last Synced: 2025-04-07T08:27:30.426Z (6 months ago)
- Topics: c-language, geodesy, geoscience, gravity-field, python, spherical-harmonics, topography
- Language: C
- Homepage: https://www.charmlib.org
- Size: 23.6 MB
- Stars: 16
- Watchers: 1
- Forks: 2
- Open Issues: 0
-
Metadata Files:
- Readme: README.rst
- Changelog: NEWS
- License: COPYING
- Authors: AUTHORS
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README
============
Introduction
============
CHarm is a C library to work with spherical harmonics up to almost arbitrarily
high degrees. The library is accompanied by a Python wrapper called PyHarm.
Features
========
* Supports real-valued fully-normalized surface and solid spherical harmonics
(the geodetic norm).
* Performs FFT-based surface spherical harmonic analysis and solid spherical
harmonic synthesis with minimized memory requirements.
* Stable up to high degrees and orders (tens of thousands and beyond).
* Available in single, double and quadruple precision.
* Supports point and mean data values (both analysis and synthesis).
* Supports synthesis at grids and at scattered points/cells. Grid-wise
computations are done by FFT whenever possible. If FFT cannot be applied,
the less efficient Chebyshev recurrences are used along the latitude
parallels instead.
* Computes the full first- and second-order gradients at evaluation points
(e.g., the gravitational vector and the gravitational tensor).
* Supports the Gauss--Legendre and Driscoll--Healy quadratures.
* Integrates solid spherical harmonic expansions (e.g., of the gravitational
potential) on band-limited irregular surfaces (e.g., on the Earth's
surface). [#f1]_
* Computes Fourier coefficients of fully-normalized associated Legendre
functions of the first kind up to ultra-high harmonic degrees.
* Supports `OpenMP `_ parallelization for
shared-memory architectures.
* Supports AVX, AVX2, AVX-512 and NEON SIMD CPU instructions to improve the
performance.
* Performs discrete FFT by `FFTW `_.
* Ships with a Python wrapper to enable high-level programming while retaining
the efficiency of the C language. The wrapper, called PyHarm, wraps CHarm
using `ctypes `_ and is fully
integrated with `numpy `_.
.. [#f1] This routine is unique to CHarm.
Installation
============
* **PyHarm (Python wrapper)**: On Linux (x86_64), macOS (x86_64, ARM64) and
Windows (x86_64), install PyHarm using ``pip``:
.. code-block:: bash
pip install pyharm
This will install PyHarm together will all the dependencies. These include
a pre-compiled CHarm library, which is internally called by PyHarm, some
other C libraries (FFTW and GOMP) and the Python package NumPy.
* **CHarm (C library)**: If you are interested in the C API, you have to build
CHarm from source. This step is not required if you plan to use the Python
interface only.
Further installation details at
`https://www.charmlib.org/build/html/install.html
`_.
.. _download:
Source code
===========
GitHub: `https://github.com/blazej-bucha/charm
`_
* Releases are pushed to ``master`` and the development happens in
``develop``.
* Tarball and zip files of releases:
`https://github.com/blazej-bucha/charm/releases
`_
Documentation
=============
The documentation of the latest version from the ``master`` branch is available
at `https://www.charmlib.org `_.
A pre-compiled HTML documentation is also available in ``docs/build/html``.
Alternatively, it can be built by executing ``make html`` after the
``configure`` call (requires ``doxygen`` and Python modules ``sphinx``,
``sphinx_book_theme`` and ``breathe``). Other formats of the documentation,
for instance, a PDF file, can be built with ``cd docs && make latexpdf``, etc.
To list all available formats, execute ``cd docs && make help``.
.. _contact:
Contact
=======
Should you have any comments, questions, bug report or criticism, please feel
free to contact the author, Blažej Bucha, at blazej.bucha@stuba.sk. Further
products developed by the author can be found at `https://www.blazejbucha.com
`_.
Pronunciation
=============
We prefer to pronounce CHarm and PyHarm like the words ``see harm`` and ``pie
harm``. But it is indeed quite charming to pronounce CHarm like the word
``charm``, especially when the library works like a charm.
Other spherical-harmonic-based libraries
========================================
Many other libraries for working with spherical harmonics are available, each
having its pros and cons. Explore! A few examples are:
* `SHTOOLS `_: Fortran95 library with Python API,
* `SHTns `_: a C library for spherical
harmonic transforms,
* `ISPACK `_: a Fortran library for
spherical harmonic transforms,
* `Libsharp `_: a C99 library for
spherical harmonic transforms,
* `healpy `_: a Python
package to handle pixelated data on the sphere building on the `HEALPix
`_ C++ library,
* `HARMONIC_SYNTH
`_: a Fortran
code for spherical harmonic synthesis written by the EGM2008 development
team.
* `SPHEREPACK
`_: a Fortran
library of spherical harmonic transforms,
* `SHAVEL `_: a program for the
spherical harmonic analysis of a horizontal vector field sampled in an
equiangular grid on a sphere
* `ICGEM `_: Online calculation service for
working with Earth and celestial gravitational models,
* `FaVeST `_: Fast Vector Spherical
Harmonic Transforms in MATLAB.
* `SHBundle
`_:
Spherical harmonic analysis and synthesis in MATLAB up to high degrees and
orders,
* `Spherical Harmonics Manipulator
`_: Spherical harmonic
synthesis in sparse points and grids (no longer maintained),
* `GrafLab `_ and `isGrafLab
`_: MATLAB-based software packages
for spherical harmonic synthesis of gravity field functionals up to high
degrees and orders (tens of thousands and well beyond).