Check invalid combination of resolution and registration in load_earth_relief (#965)

*Add check to see the registration type when passing a registration type for a specific resolution, and raise an error if an invalid registration is passed.
*Add a test to confirm an error is raised when an invalid registration is passed.

Co-authored-by: Will Schlitzer <schlitzer90@gmail.com>

Author: seisman

pygmt/datasets/earth_relief.py

@@ -23,9 +23,11 @@ def load_earth_relief(resolution="01d", region=None, registration=None):
     These grids can also be accessed by passing in the file name
     **@earth_relief**\_\ *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-docs:`datasets/remote-data.html` for more
-    details.
+    registration type (**p** for pixel registration or **g** for gridline
+    registration).
+
+    Refer to :gmt-docs:`datasets/remote-data.html#global-earth-relief-grids`
+    for more details.
 
     Parameters
     ----------
@@ -37,8 +39,10 @@ def load_earth_relief(resolution="01d", region=None, registration=None):
         or ``'01s'``.
 
     region : str or list
-        The subregion of the grid to load. Required for Earth relief grids with
-        resolutions higher than 5 arc-minute (i.e., ``05m``).
+        The subregion of the grid to load, in the forms of a list
+        [*xmin*, *xmax*, *ymin*, *ymax*] or a string *xmin/xmax/ymin/ymax*.
+        Required for Earth relief grids with resolutions higher than 5
+        arc-minute (i.e., ``05m``).
 
     registration : str
         Grid registration type. Either ``pixel`` for pixel registration or
@@ -81,7 +85,7 @@ def load_earth_relief(resolution="01d", region=None, registration=None):
         reg = f"_{registration[0]}" if registration else ""
     else:
         raise GMTInvalidInput(
-            f"Invalid grid registration: {registration}, should be either "
+            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."
@@ -90,6 +94,15 @@ def load_earth_relief(resolution="01d", region=None, registration=None):
     if resolution not in non_tiled_resolutions + tiled_resolutions:
         raise GMTInvalidInput(f"Invalid Earth relief resolution '{resolution}'.")
 
+    # Check combination of resolution and registeration.
+    if (resolution == "15s" and registration == "gridline") or (
+        resolution in ("03s", "01s") and registration == "pixel"
+    ):
+        raise GMTInvalidInput(
+            f"{registration}-registered Earth relief data for "
+            f"resolution '{resolution}' is not supported."
+        )
+
     # different ways to load tiled and non-tiled earth relief data
     # Known issue: tiled grids don't support slice operation
     # See https://github.com/GenericMappingTools/pygmt/issues/524

pygmt/tests/test_datasets.py

@@ -146,3 +146,17 @@ def test_earth_relief_incorrect_registration():
     """
     with pytest.raises(GMTInvalidInput):
         load_earth_relief(registration="improper_type")
+
+
+def test_earth_relief_invalid_resolution_registration_combination():
+    """
+    Test loading earth relief with invalid combination of resolution and
+    registration.
+    """
+    for resolution, registration in [
+        ("15s", "gridline"),
+        ("03s", "pixel"),
+        ("01s", "pixel"),
+    ]:
+        with pytest.raises(GMTInvalidInput):
+            load_earth_relief(resolution=resolution, registration=registration)