Create a copy of the RasterLayer object
Substitute NA values with 0 values in RasterLayer copy
Create a SpatialPixelsDataFrame from the no-NA data
Change the column names to a standard set of labels
Modify the object names supplied as ggplot aesthetics
Get UTM_gridded_values from the no-NA SPDF
Force LU category values to be 50 if terrain shows water
Replace 'CALMET_categories' vector with revised values