For mapping purpose, one need to store RG=f(I,J) data into the Regular Grid array and to define a linear correspondence between the User Coordinate Space and the indices I and J, X=x(I) and Y=y(I). All this is done using command RGDATA to read a purposely formatted file. Contrary to the X Y Z buffers which are Real*8, the Regular Grid RG array is declared Real*4 as there is usually no meaning in defining contours with very high precision.
The Regular Grid array is loaded using command
GREG2RGDATA Name [/VARIABLE]
where Name is a variable or the input file name if the /VARIABLE option is not present.