This internal function checks that coords (as passed to functions) is a valid set of names, or, if NULL, that we have standard variable names in data
check_coords_names(data, coords)
A vector of length 2 with the valid names, in the correct order
a data.frame containing the locations.
a vector of length two giving the names of the "x" and "y" coordinates, of points is a data.frame and does not use standard names.