[ncl-talk] Difference plot in NCL

[Maria Gehne - NOAA Affiliate]

Hi Partha,

you can try setting all values <0.2 to _FillValue in both arrays and then
taking the difference. This will only take the difference at points where
both arrays have values >0.2. So if for example your two arrays are Y and X
and both are 2D you could try:

X at _FillValue = default_fillvalue(typeof(X)) ( or maybe it already has a
fill value attached, then there is no need for this)
Y at _FillValue = default_fillvalue(typeof(Y))

D = X ( just to copy the fill value and other meta data)


X = where(X.lt.0.2,X at _FillValue,X)
Y = where(Y.lt.0.2,Y at _FillValue,Y)
D = X-Y

This should now have missing values where either X or Y are <0.2 and those
will not be plotted.

Maria



On Fri, Aug 29, 2014 at 1:18 PM, Partha Bhattacharjee <pbhatta2 at jhu.edu>
wrote:

>  ​Dear NCL,
>
>
>   I want to plot a difference between two model outputs (see the attached
> figure). In both plots, >0.2 (in the colorbar) are subject of interest.
>  Simple difference plot shows difference in <0.2 background also. How do I
> specifically plot difference keeping background <0.2 at constant in NCL?
>
>
>   Thanks,
>
>  Partha
>
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