Set gridline (if available) as the default grid registration for remote datasets

pygmt/datasets/load_remote_dataset.py

@@ -230,20 +230,22 @@ def _load_remote_dataset(
     The returned :class:`xarray.DataArray` doesn't support slice operation for
     tiled grids.
     """
-
-    if registration in ("pixel", "gridline", None):
+    dataset = datasets[dataset_name]
+    if resolution not in dataset.resolutions.keys():
+        raise GMTInvalidInput(f"Invalid resolution '{resolution}'.")
+    if registration is None:
+        registration = dataset.resolutions[resolution].registrations[0]
+    if registration in ("pixel", "gridline"):
         # If None, let GMT decide on Pixel/Gridline type
-        reg = f"_{registration[0]}" if registration else ""
+        reg = f"_{registration[0]}"
     else:
         raise GMTInvalidInput(
             f"Invalid grid registration: '{registration}', should be either "
             "'pixel', 'gridline' or None. Default is None, where a "
             "pixel-registered grid is returned unless only the "
             "gridline-registered grid is available."
         )
-    dataset = datasets[dataset_name]
-    if resolution not in dataset.resolutions.keys():
-        raise GMTInvalidInput(f"Invalid resolution '{resolution}'.")
+
     if registration and (
         registration not in dataset.resolutions[resolution].registrations
     ):

pygmt/tests/test_datasets_earth_age.py

@@ -31,12 +31,13 @@ def test_earth_age_01d():
     """
     Test some properties of the earth age 01d data.
     """
-    data = load_earth_age(resolution="01d", registration="gridline")
+    data = load_earth_age(resolution="01d")
     assert data.name == "seafloor_age"
     assert data.attrs["units"] == "Myr"
     assert data.attrs["long_name"] == "age of seafloor crust"
     assert data.attrs["horizontal_datum"] == "WGS84"
     assert data.shape == (181, 361)
+    assert data.gmt.registration == 0
     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(), 0.167381, rtol=1e-5)
@@ -51,6 +52,7 @@ def test_earth_age_01d_with_region():
         resolution="01d", region=[-10, 10, -5, 5], registration="gridline"
     )
     assert data.shape == (11, 21)
+    assert data.gmt.registration == 0
     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(), 11.293945)

pygmt/tests/test_datasets_earth_relief.py

@@ -27,14 +27,13 @@ def test_earth_relief_01d_igpp_synbath(data_source):
     Test some properties of the earth relief 01d data with IGPP and SYNBATH
     data.
     """
-    data = load_earth_relief(
-        resolution="01d", registration="gridline", data_source=data_source
-    )
+    data = load_earth_relief(resolution="01d", data_source=data_source)
     assert data.name == "elevation"
     assert data.attrs["units"] == "meters"
     assert data.attrs["long_name"] == "Earth elevation relative to the geoid"
     assert data.attrs["vertical_datum"] == "EGM96"
     assert data.attrs["horizontal_datum"] == "WGS84"
+    assert data.gmt.registration == 0
     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))
@@ -132,6 +131,7 @@ def test_earth_gebcosi_15m_with_region():
         data_source="gebcosi",
     )
     assert data.shape == (16, 8)
+    assert data.gmt.registration == 1
     npt.assert_allclose(data.lat, np.arange(-87.875, -84, 0.25))
     npt.assert_allclose(data.lon, np.arange(85.125, 87, 0.25))
     npt.assert_allclose(data.min(), -531)