Add load_earth_vertical_gravity_gradient function for Earth vertical gravity gradient dataset

doc/api/index.rst

@@ -226,6 +226,7 @@ and store them in GMT's user data directory.
     datasets.load_earth_geoid
     datasets.load_earth_magnetic_anomaly
     datasets.load_earth_relief
+    datasets.load_earth_vertical_gravity_gradient
     datasets.load_sample_data
 
 The following functions are deprecated since v0.6.0 and will be removed in v0.9.0.

pygmt/datasets/__init__.py

@@ -7,6 +7,9 @@
 from pygmt.datasets.earth_geoid import load_earth_geoid
 from pygmt.datasets.earth_magnetic_anomaly import load_earth_magnetic_anomaly
 from pygmt.datasets.earth_relief import load_earth_relief
+from pygmt.datasets.earth_vertical_gravity_gradient import (
+    load_earth_vertical_gravity_gradient,
+)
 from pygmt.datasets.samples import (
     list_sample_data,
     load_fractures_compilation,

pygmt/datasets/earth_vertical_gravity_gradient.py

@@ -0,0 +1,71 @@
+"""
+Function to download the IGPP Global Earth Vertical Gravity Gradient from the
+GMT data server, and load as :class:`xarray.DataArray`.
+
+The grids are available in various resolutions.
+"""
+from pygmt.datasets.load_remote_dataset import _load_remote_dataset
+from pygmt.helpers import kwargs_to_strings
+
+
+@kwargs_to_strings(region="sequence")
+def load_earth_vertical_gravity_gradient(
+    resolution="01d", region=None, registration=None
+):
+    r"""
+    Load the IGPP Global Earth Vertical Gravity Gradient in various
+    resolutions.
+
+    The grids are downloaded to a user data directory
+    (usually ``~/.gmt/server/earth/earth_vgg/``) the first time you invoke
+    this function. Afterwards, it will load the grid from the data directory.
+    So you'll need an internet connection the first time around.
+
+    These grids can also be accessed by passing in the file name
+    **@earth_vgg**\_\ *res*\[_\ *reg*] to any grid plotting/processing
+    function. *res* is the grid resolution (see below), and *reg* is grid
+    registration type (**p** for pixel registration or **g** for gridline
+    registration).
+
+    Refer to :gmt-datasets:`earth-vgg.html` for more details.
+
+    Parameters
+    ----------
+    resolution : str
+        The grid resolution. The suffix ``d`` and ``m`` stand for
+        arc-degrees and arc-minutes. It can be ``"01d"``, ``"30m"``,
+        ``"20m"``, ``"15m"``, ``"10m"``, ``"06m"``, ``"05m"``, ``"04m"``,
+        ``"03m"``, ``"02m"``, or ``"01m"``.
+
+    region : str or list
+        The subregion of the grid to load, in the form of a list
+        [*xmin*, *xmax*, *ymin*, *ymax*] or a string *xmin/xmax/ymin/ymax*.
+        Required for grids with resolutions higher than 5
+        arc-minutes (i.e., ``"05m"``).
+
+    registration : str
+        Grid registration type. Either ``"pixel"`` for pixel registration or
+        ``"gridline"`` for gridline registration. Default is ``None``, where
+        a pixel-registered grid is returned unless only the
+        gridline-registered grid is available.
+
+    Returns
+    -------
+    grid : :class:`xarray.DataArray`
+        The Earth vertical gravity gradient grid. Coordinates are latitude and
+        longitude in degrees. Units are in Eotvos.
+
+    Note
+    ----
+    The :class:`xarray.DataArray` grid doesn't support slice operation, for
+    Earth vertical gravity gradient grids with resolutions of 5 arc-minutes or
+    higher, which are stored as smaller tiles.
+    """
+    grid = _load_remote_dataset(
+        dataset_name="earth_vgg",
+        dataset_prefix="earth_vgg_",
+        resolution=resolution,
+        region=region,
+        registration=registration,
+    )
+    return grid

pygmt/datasets/load_remote_dataset.py

@@ -167,6 +167,26 @@ class GMTRemoteDataset(NamedTuple):
             "01m": Resolution(["pixel"], True),
         },
     ),
+    "earth_vgg": GMTRemoteDataset(
+        title="Earth vertical gravity gradient",
+        name="earth_vgg",
+        long_name="IGPP Global Earth Vertical Gravity Gradient",
+        units="Eotvos",
+        extra_attributes={"horizontal_datum": "WGS84"},
+        resolutions={
+            "01d": Resolution(["pixel", "gridline"], False),
+            "30m": Resolution(["pixel", "gridline"], False),
+            "20m": Resolution(["pixel", "gridline"], False),
+            "15m": Resolution(["pixel", "gridline"], False),
+            "10m": Resolution(["pixel", "gridline"], False),
+            "06m": Resolution(["pixel", "gridline"], False),
+            "05m": Resolution(["pixel", "gridline"], True),
+            "04m": Resolution(["pixel", "gridline"], True),
+            "03m": Resolution(["pixel", "gridline"], True),
+            "02m": Resolution(["pixel", "gridline"], True),
+            "01m": Resolution(["pixel"], True),
+        },
+    ),
 }
 
 

pygmt/helpers/testing.py

@@ -191,6 +191,9 @@ def download_test_data():
         # Earth free-air anomaly grids
         "@earth_faa_01d_g",
         "@S90W180.earth_faa_05m_g.nc",  # Specific grid for 05m test
+        # Earth vertical gravity gradient grids
+        "@earth_vgg_01d_g",
+        "@S90W180.earth_vgg_05m_g.nc",  # Specific grid for 05m test
         # Other cache files
         "@capitals.gmt",
         "@earth_relief_20m_holes.grd",

pygmt/tests/test_datasets_earth_vertical_gravity_gradient.py

@@ -0,0 +1,98 @@
+"""
+Test basic functionality for loading Earth vertical gravity gradient datasets.
+"""
+import numpy as np
+import numpy.testing as npt
+import pytest
+from pygmt.datasets import load_earth_vertical_gravity_gradient
+from pygmt.exceptions import GMTInvalidInput
+
+
+def test_earth_vertical_gravity_gradient_fails():
+    """
+    Make sure load_earth_vertical_gravity_gradient fails for invalid
+    resolutions.
+    """
+    resolutions = "1m 1d bla 60d 001m 03".split()
+    resolutions.append(60)
+    for resolution in resolutions:
+        with pytest.raises(GMTInvalidInput):
+            load_earth_vertical_gravity_gradient(resolution=resolution)
+
+
+def test_earth_vertical_gravity_gradient_incorrect_registration():
+    """
+    Test loading load_earth_vertical_gravity_gradient with incorrect
+    registration type.
+    """
+    with pytest.raises(GMTInvalidInput):
+        load_earth_vertical_gravity_gradient(registration="improper_type")
+
+
+def test_earth_vertical_gravity_gradient_01d():
+    """
+    Test some properties of the earth vgg 01d data.
+    """
+    data = load_earth_vertical_gravity_gradient(
+        resolution="01d", registration="gridline"
+    )
+    assert data.name == "earth_vgg"
+    assert data.attrs["units"] == "Eotvos"
+    assert data.attrs["long_name"] == "IGPP Global Earth Vertical Gravity Gradient"
+    assert data.attrs["horizontal_datum"] == "WGS84"
+    assert data.shape == (181, 361)
+    npt.assert_allclose(data.lat, np.arange(-90, 91, 1))
+    npt.assert_allclose(data.lon, np.arange(-180, 181, 1))
+    npt.assert_allclose(data.min(), -136.34375)
+    npt.assert_allclose(data.max(), 104.59375)
+    assert data[1, 1].isnull()
+
+
+def test_earth_vertical_gravity_gradient_01d_with_region():
+    """
+    Test loading low-resolution earth vgg with 'region'.
+    """
+    data = load_earth_vertical_gravity_gradient(
+        resolution="01d", region=[-10, 10, -5, 5], registration="gridline"
+    )
+    assert data.shape == (11, 21)
+    npt.assert_allclose(data.lat, np.arange(-5, 6, 1))
+    npt.assert_allclose(data.lon, np.arange(-10, 11, 1))
+    npt.assert_allclose(data.min(), -16.34375)
+    npt.assert_allclose(data.max(), 19.78125)
+
+
+def test_earth_vertical_gravity_gradient_05m_with_region():
+    """
+    Test loading a subregion of high-resolution earth vgg.
+    """
+    data = load_earth_vertical_gravity_gradient(
+        resolution="05m", region=[-50, -40, 20, 26], registration="gridline"
+    )
+    assert data.coords["lat"].data.min() == 20.0
+    assert data.coords["lat"].data.max() == 26.0
+    assert data.coords["lon"].data.min() == -50.0
+    assert data.coords["lon"].data.max() == -40.0
+    npt.assert_allclose(data.min(), -107.625)
+    npt.assert_allclose(data.max(), 159.75)
+    assert data.sizes["lat"] == 73
+    assert data.sizes["lon"] == 121
+
+
+def test_earth_vertical_gravity_gradient_05m_without_region():
+    """
+    Test loading high-resolution earth vgg without passing 'region'.
+    """
+    with pytest.raises(GMTInvalidInput):
+        load_earth_vertical_gravity_gradient("05m")
+
+
+def test_earth_vertical_gravity_gradient_incorrect_resolution_registration():
+    """
+    Test that an error is raised when trying to load a grid registration with
+    an unavailable resolution.
+    """
+    with pytest.raises(GMTInvalidInput):
+        load_earth_vertical_gravity_gradient(
+            resolution="01m", region=[0, 1, 3, 5], registration="gridline"
+        )