Raise RuntimeWarning instead of an exception for irregular grid spacing (#1530)

* Raise a warning intsead an exception for irregular grid spacing
* Calcuate grid spacing if irregular spacing is detected
* Update pygmt/tests/test_clib.py

Co-authored-by: Wei Ji <[email protected]>

Co-authored-by: Wei Ji <[email protected]>

Author: seisman

pygmt/clib/conversion.py

@@ -1,6 +1,8 @@
 """
 Functions to convert data types into ctypes friendly formats.
 """
+import warnings
+
 import numpy as np
 import pandas as pd
 from pygmt.exceptions import GMTInvalidInput
@@ -95,9 +97,14 @@ def dataarray_to_matrix(grid):
         coord_incs = coord[1:] - coord[0:-1]
         coord_inc = coord_incs[0]
         if not np.allclose(coord_incs, coord_inc):
-            raise GMTInvalidInput(
-                f"Grid appears to have irregular spacing in the '{dim}' dimension."
+            # calculate the increment if irregular spacing is found
+            coord_inc = (coord[-1] - coord[0]) / (coord.size - 1)
+            msg = (
+                f"Grid may have irregular spacing in the '{dim}' dimension, "
+                "but GMT only supports regular spacing. Calculated regular spacing "
+                f"{coord_inc} is assumed in the '{dim}' dimension."
             )
+            warnings.warn(msg, category=RuntimeWarning)
         if coord_inc == 0:
             raise GMTInvalidInput(
                 f"Grid has a zero increment in the '{dim}' dimension."

pygmt/tests/test_clib.py

@@ -805,16 +805,18 @@ def test_dataarray_to_matrix_dims_fails():
         dataarray_to_matrix(grid)
 
 
-def test_dataarray_to_matrix_inc_fails():
+def test_dataarray_to_matrix_irregular_inc_warning():
     """
-    Check that it fails for variable increments.
+    Check that it warns for variable increments, see also
+    https://github.com/GenericMappingTools/pygmt/issues/1468.
     """
     data = np.ones((4, 5), dtype="float64")
     x = np.linspace(0, 1, 5)
     y = np.logspace(2, 3, 4)
     grid = xr.DataArray(data, coords=[("y", y), ("x", x)])
-    with pytest.raises(GMTInvalidInput):
+    with pytest.warns(expected_warning=RuntimeWarning) as record:
         dataarray_to_matrix(grid)
+        assert len(record) == 1
 
 
 def test_dataarray_to_matrix_zero_inc_fails():