Fix the spacing parameter and check required parameters in xyz2grd

Author: seisman

pygmt/src/xyz2grd.py

@@ -30,7 +30,7 @@
     r="registration",
     w="wrap",
 )
-@kwargs_to_strings(R="sequence")
+@kwargs_to_strings(I="sequence", R="sequence")
 def xyz2grd(data=None, x=None, y=None, z=None, **kwargs):
     r"""
     Create a grid file from table data.
@@ -132,6 +132,9 @@ def xyz2grd(data=None, x=None, y=None, z=None, **kwargs):
         - None if ``outgrid`` is set (grid output will be stored in file set by
           ``outgrid``)
     """
+    if "I" not in kwargs or "R" not in kwargs:
+        raise GMTInvalidInput("Both 'region' and 'spacing' must be specified.")
+
     with GMTTempFile(suffix=".nc") as tmpfile:
         with Session() as lib:
             file_context = lib.virtualfile_from_data(