From 95f28fc7fe66caebf77eefe045f45686a0d56b18 Mon Sep 17 00:00:00 2001
From: Wei Ji <23487320+weiji14@users.noreply.github.com>
Date: Wed, 13 Oct 2021 15:48:20 +1300
Subject: [PATCH 1/2] Allow GMTDataArrayAccessor to work on sliced datacubes

If `grdinfo` can't read the source NetCDF file as it
is an n-dimensional datacube (instead of a 2D grid),
we fallback to setting the default gridline registration
and Cartesian grid type.
---
 pygmt/accessors.py           |  2 +-
 pygmt/tests/test_accessor.py | 24 ++++++++++++++++++++++++
 2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/pygmt/accessors.py b/pygmt/accessors.py
index 59fd7aa13e6..190524075f9 100644
--- a/pygmt/accessors.py
+++ b/pygmt/accessors.py
@@ -34,7 +34,7 @@ def __init__(self, xarray_obj):
             self._registration, self._gtype = map(
                 int, grdinfo(self._source, per_column="n", o="10,11").split()
             )
-        except KeyError:
+        except (KeyError, ValueError):
             self._registration = 0  # Default to Gridline registration
             self._gtype = 0  # Default to Cartesian grid type
 
diff --git a/pygmt/tests/test_accessor.py b/pygmt/tests/test_accessor.py
index a3b0dc4fafc..cb6bf432a9b 100644
--- a/pygmt/tests/test_accessor.py
+++ b/pygmt/tests/test_accessor.py
@@ -1,6 +1,8 @@
 """
 Test the behaviour of the GMTDataArrayAccessor class.
 """
+import os
+
 import pytest
 import xarray as xr
 from pygmt import which
@@ -66,3 +68,25 @@ def test_accessor_set_non_boolean():
 
     with pytest.raises(GMTInvalidInput):
         grid.gmt.gtype = 2
+
+
+def test_accessor_sliced_datacube():
+    """
+    Check that a 2D grid which is sliced from an n-dimensional datacube works
+    with accessor methods.
+
+    This is a regression test for
+    https://github.com/GenericMappingTools/pygmt/issues/1578.
+    """
+    try:
+        fname = which(
+            "https://github.com/pydata/xarray-data/raw/master/eraint_uvz.nc",
+            download="u",
+        )
+        dataset = xr.open_dataset(fname)
+        grid = dataset.sel(level=500, month=1, drop=True).z
+
+        assert grid.gmt.registration == 0  # gridline registration
+        assert grid.gmt.gtype == 0  # cartesian coordinate type
+    finally:
+        os.remove(fname)

From 81145dbb9d62079046ae4f7d26d0dc53ff70cbf0 Mon Sep 17 00:00:00 2001
From: Wei Ji <23487320+weiji14@users.noreply.github.com>
Date: Fri, 22 Oct 2021 13:57:59 +1300
Subject: [PATCH 2/2] Use with statement to ensure the grid is properly closed

So that the file can be deleted on Windows.
---
 pygmt/tests/test_accessor.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/pygmt/tests/test_accessor.py b/pygmt/tests/test_accessor.py
index cb6bf432a9b..99ce5f7104a 100644
--- a/pygmt/tests/test_accessor.py
+++ b/pygmt/tests/test_accessor.py
@@ -83,8 +83,8 @@ def test_accessor_sliced_datacube():
             "https://github.com/pydata/xarray-data/raw/master/eraint_uvz.nc",
             download="u",
         )
-        dataset = xr.open_dataset(fname)
-        grid = dataset.sel(level=500, month=1, drop=True).z
+        with xr.open_dataset(fname) as dataset:
+            grid = dataset.sel(level=500, month=1, drop=True).z
 
         assert grid.gmt.registration == 0  # gridline registration
         assert grid.gmt.gtype == 0  # cartesian coordinate type