Implement our own FFT functions for xr.DataArray

.github/environment.yml

@@ -13,7 +13,6 @@ dependencies:
   - numba>=0.57
   - xarray>=2022.03
   - verde>=1.9.0
-  - xrft>=1.0
   - choclo>=0.1
   - boule>=0.6.0
   - bordado>=0.4.0

README.md

@@ -52,9 +52,8 @@ Things that will *not* be covered in Harmonica:
 - Multi-physics partial differential equation solvers. Use
   [SimPEG](http://www.simpeg.xyz/) or [PyGIMLi](https://www.pygimli.org/)
   instead.
-- Generic grid processing methods (like FFT and standard interpolation).
-  We'll rely on [Verde](https://www.fatiando.org/verde),
-  [xrft](https://xrft.readthedocs.io/en/latest/) and
+- Generic grid processing methods (like standard interpolation).
+  We'll rely on [Verde](https://www.fatiando.org/verde) and
   [xarray](https://xarray.dev) for those.
 - Data visualization.
 - GUI applications.

doc/api/index.rst

@@ -51,8 +51,15 @@ Define filters in the frequency domain.
     filters.gaussian_highpass_kernel
     filters.reduction_to_pole_kernel
 
-Use :func:`xrft.xrft.fft` and :func:`xrft.xrft.ifft` to apply Fast-Fourier
-Transforms and its inverse on :class:`xarray.DataArray`.
+FFT and padding functions that can be used with 2D :class:`xarray.DataArray`:
+
+.. autosummary::
+    :toctree: generated/
+
+    filters.fft
+    filters.ifft
+    filters.pad
+    filters.unpad
 
 Equivalent Sources
 ------------------

doc/conf.py

@@ -49,7 +49,6 @@
     "scipy": ("https://docs.scipy.org/doc/scipy/reference", None),
     "pandas": ("http://pandas.pydata.org/pandas-docs/stable/", None),
     "xarray": ("http://xarray.pydata.org/en/stable/", None),
-    "xrft": ("https://xrft.readthedocs.io/en/stable/", None),
     "pooch": ("https://www.fatiando.org/pooch/latest/", None),
     "ensaio": ("https://www.fatiando.org/ensaio/latest/", None),
     "verde": ("https://www.fatiando.org/verde/latest/", None),

doc/install.rst

@@ -75,7 +75,6 @@ Required:
 * `verde <http://www.fatiando.org/verde/>`__
 * `bordado <http://www.fatiando.org/bordado/>`__
 * `boule <http://www.fatiando.org/boule/>`__
-* `xrft <https://xrft.readthedocs.io/>`__
 * `choclo <http://www.fatiando.org/choclo/>`__
 * `boule <http://www.fatiando.org/boule/>`__
 
@@ -98,4 +97,4 @@ The examples in the :ref:`gallery` also use:
 * `ensaio <http://www.fatiando.org/ensaio/>`__ for downloading sample datasets
 * `pygmt <https://www.pygmt.org/>`__ and `matplotlib <https://matplotlib.org/>`__ for plotting maps and figures
 * `pyproj <https://jswhit.github.io/pyproj/>`__ for cartographic projections
-* `bordado <http://www.fatiando.org/bordado/>`__ for working with geographic coordinates
+* `bordado <http://www.fatiando.org/bordado/>`__ for working with geographic coordinates

doc/overview.rst

@@ -19,8 +19,7 @@ Harmonica *will not* provide:
   instead.
 - Generic processing methods like grid transformations (use `Verde
   <https://www.fatiando.org/verde>`__ or `Xarray <https://docs.xarray.dev>`__
-  instead) or multidimensional FFT calculations (use `xrft
-  <https://xrft.readthedocs.io>`__ instead).
+  instead).
 - Reference ellipsoid representations and computations like normal gravity. Use
   `Boule <https://www.fatiando.org/boule>`__ instead.
 - Data visualization functions. Use `matplotlib <https://matplotlib.org/>`__

env/requirements-tests.txt

@@ -5,3 +5,4 @@ coverage
 pyvista
 vtk>=9
 numba_progress
+xrft

environment.yml

@@ -15,7 +15,6 @@ dependencies:
   - scikit-learn
   - verde>=1.8.1
   - xarray
-  - xrft>=1.0
   - choclo>=0.1
   - boule>=0.6
   - bordado>=0.4.0
@@ -27,6 +26,7 @@ dependencies:
   - pytest
   - pytest-cov
   - coverage
+  - xrft
   # Documentation requirements
   - sphinx==7.2.*
   - numpydoc==1.7.*

pyproject.toml

@@ -37,7 +37,6 @@ dependencies = [
     "numba >= 0.57",
     "xarray >= 2022.03",
     "verde >= 1.8.1",
-    "xrft >= 1.0",
     "choclo >= 0.1",
     "boule >= 0.6.0",
     "bordado >= 0.4.0",

src/harmonica/_transformations.py

@@ -11,6 +11,7 @@
 import numpy as np
 
 from .filters._filters import (
+    apply_filter,
     derivative_easting_kernel,
     derivative_northing_kernel,
     derivative_upward_kernel,
@@ -19,7 +20,7 @@
     reduction_to_pole_kernel,
     upward_continuation_kernel,
 )
-from .filters._utils import apply_filter, grid_sanity_checks
+from .filters._utils import grid_sanity_checks
 
 
 def derivative_upward(grid, *, order=1, pad=True, pad_kwargs=None):

src/harmonica/filters/__init__.py

@@ -8,6 +8,7 @@
 Frequency domain filters meant to be applied on regular grids.
 """
 
+from ._fft import fft, ifft
 from ._filters import (
     derivative_easting_kernel,
     derivative_northing_kernel,
@@ -17,3 +18,4 @@
     reduction_to_pole_kernel,
     upward_continuation_kernel,
 )
+from ._padding import pad, unpad