[gradsusr] Help: How to interpolate multiple shaded area into each other?

[얍준후이]

Hi all,
I would like to interpolate the three shaded area into each other. But how to do this in GrADS? My client said this should can be done by using a GrADS built-in function.
But I have searched for the whole document index, but fail to see any options for that.
Any help?
Regards, JH
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