Try using GMT_GRID_PIXEL_REG as default instead of GMT_GRID_NODE_REG

Trying to use pixel registration as the default when converting an xarray.DataArray to a virtual GMT grid, instead of gridline registration.

pygmt/clib/conversion.py

@@ -102,7 +102,7 @@ def dataarray_to_matrix(grid):
                     dim
                 )
             )
-        region.extend([coord.min(), coord.max()])
+        region.extend([coord.min() - coord_inc / 2, coord.max() + coord_inc / 2])
         inc.append(coord_inc)
 
     if any([i < 0 for i in inc]):  # Sort grid when there are negative increments

pygmt/clib/session.py

@@ -531,7 +531,7 @@ def create_data(self, family, geometry, mode, **kwargs):
         registration : int
             The node registration (what the coordinates mean). Can be
             ``'GMT_GRID_PIXEL_REG'`` or ``'GMT_GRID_NODE_REG'``. Defaults to
-            ``'GMT_GRID_NODE_REG'``.
+            ``'GMT_GRID_PIXEL_REG'``.
         pad : int
             The grid padding. Defaults to ``GMT_PAD_DEFAULT``.
 
@@ -565,7 +565,7 @@ def create_data(self, family, geometry, mode, **kwargs):
         )
         geometry_int = self._parse_constant(geometry, valid=GEOMETRIES)
         registration_int = self._parse_constant(
-            kwargs.get("registration", "GMT_GRID_NODE_REG"), valid=REGISTRATIONS
+            kwargs.get("registration", "GMT_GRID_PIXEL_REG"), valid=REGISTRATIONS
         )
 
         # Convert dim, ranges, and inc to ctypes arrays if given (will be None
@@ -1171,7 +1171,7 @@ def virtualfile_from_matrix(self, matrix):
             yield vfile
 
     @contextmanager
-    def virtualfile_from_grid(self, grid, registration="GMT_GRID_NODE_REG"):
+    def virtualfile_from_grid(self, grid, registration="GMT_GRID_PIXEL_REG"):
         """
         Store a grid in a virtual file.