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20040817: No Interpolation with GDPLOT2



Charles,

I'm assuming you have converted the grid to GEMPAK using NAGRIB.
The NAGRIB decoder that converts from the staggared grid to
the regular grid will interpolate the alternating grid points.
Those values would be interpolated before any plotting routine
(which you would see with GDLIST. The intepolation in NAGRIB is 
usingcenetered differences (except on the edges).

If this is the case, you can use the SGT/SLT (or BOOL/MASK) functions
to establish a value above which you treat the value as "1"
(by dividing by the value (eg QUO ( SGT ( LAND, .5 ), LAND ).

Steve Chiswell
Unidata User Support

>From: "Charles J. Alonge" <address@hidden>
>Organization: SAIC - NASA Goddard Space Flight Center
>Keywords: 200408172042.i7HKgGaW009114

>Hello Support,
> 
>    I am trying to plot vegetation type, soil type, and land/sea
><>masks gridded data sets on the native Arakawa E grid (ETA).  When I 
>use gdplot2 I continuously get an interpolated data set.  That would be 
>fine for most of the fields, except for the above because they consist 
>of integer class values and should not be interpolated.  I want to fill 
>the entire grid box with its value,
>instead of doing any interpolation from grid box to grid box.  I thought
><>that setting type="Z" would achieve this, but interpolation between 
>grid values still exists when mapped by gdplot2.  Any assistance will be 
>greatly appreciated.
>
>Charles
>
>-- 
>
>Charles J. Alonge
>SAIC - NASA Goddard Space Flight Center
>Hydrological Sciences Branch
>NASA-GSFC Mail Code 974.1
>Greenbelt, MD 20771
>
>Office: Building 22, Room 008
>Phone:  (301) 286-8272
>Fax:    (301) 286-8624
>Email:  address@hidden
>
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