Refactor load_remote_dataset using the special read module

Author: seisman

pygmt/datasets/load_remote_dataset.py

@@ -6,10 +6,10 @@
 
 from typing import TYPE_CHECKING, ClassVar, NamedTuple
 
+from pygmt.clib import Session
 from pygmt.exceptions import GMTInvalidInput
-from pygmt.helpers import kwargs_to_strings
-from pygmt.io import load_dataarray
-from pygmt.src import grdcut, which
+from pygmt.helpers import build_arg_list, kwargs_to_strings
+from pygmt.src import which
 
 if TYPE_CHECKING:
     import xarray as xr
@@ -406,18 +406,27 @@ def _load_remote_dataset(
         )
     reg = f"_{registration[0]}"
 
-    # different ways to load tiled and non-tiled grids.
-    # Known issue: tiled grids don't support slice operation
-    # See https://github.com/GenericMappingTools/pygmt/issues/524
-    if region is None:
-        if dataset.resolutions[resolution].tiled:
+    fname = f"@{dataset_prefix}{resolution}{reg}"
+    if dataset.resolutions[resolution].tiled:
+        if region is None:
             raise GMTInvalidInput(
                 f"'region' is required for {dataset.title} resolution '{resolution}'."
             )
-        fname = which(f"@{dataset_prefix}{resolution}{reg}", download="a")
-        grid = load_dataarray(fname, engine="netcdf4")
+        fullname = None
     else:
-        grid = grdcut(f"@{dataset_prefix}{resolution}{reg}", region=region)
+        fullname = which(fname, download="a")
+
+    # Currently, only grids are supported. Should support images in the future.
+    kwdict = {"T": "g", "R": region}  # region can be None
+    with Session() as lib:
+        with lib.virtualfile_out(kind="grid") as voutgrd:
+            lib.call_module(
+                module="read",
+                args=[fname, voutgrd, *build_arg_list(kwdict)],
+            )
+            grid = lib.virtualfile_to_raster(outgrid=None, vfname=voutgrd)
+    if fullname is not None:
+        grid.encoding["source"] = fullname
 
     # Add some metadata to the grid
     grid.name = dataset.name

pygmt/tests/test_accessor.py

@@ -115,9 +115,8 @@ def test_accessor_grid_source_file_not_exist():
     # Registration and gtype are correct
     assert grid.gmt.registration == 1
     assert grid.gmt.gtype == 1
-    # The source grid file is defined but doesn't exist
-    assert grid.encoding["source"].endswith(".nc")
-    assert not Path(grid.encoding["source"]).exists()
+    # The source grid file is undefined.
+    assert grid.encoding.get("source") is None
 
     # For a sliced grid, fallback to default registration and gtype,
     # because the source grid file doesn't exist.