[gradsusr] Setting missing values (or any value) to undefined

[Jennifer Adams]

Only one UNDEF value is allowed per data set. The workaround if there is more than one in your data is to use maskout() and/or const(). 

However, with ‘dtype netcdf’ descriptors, you can put the name of the attribute that contains the missing value in the UNDEF entry, and then GrADS can support different undef values for different variables in the same file. See the paragraph next to UNDEF in http://iges.org/grads/gadoc/SDFdescriptorfile.html

—Jennifer

On Oct 30, 2015, at 12:58 PM, Matt Bunkers - WFO UNR <matthew.bunkers at noaa.gov> wrote:

> Setting the UNDEF variable in the ctl file worked for me.  Still, I wonder if more than one UNDEF variable can be defined.
> 
> -- Matt
> 
> 
> On Fri, Oct 30, 2015 at 10:40 AM, Matt Bunkers - WFO UNR <matthew.bunkers at noaa.gov> wrote:
> The maskout(WC,WC+119.9) option didn't work.  I've tried playing with different numbers but still get weird gradients.
> 
> Can I include more than one value for the UNDEF variable in the ctl file?  The documentation doesn't suggest so.
> 
> Thanks,
> 
> -- Matt
> 
> 
> On Fri, Oct 30, 2015 at 10:14 AM, Goodson,Ron [Edm] <Ron.Goodson at ec.gc.ca> wrote:
> If this is the only data being analyzed .. then wouldn’t just setting UNDEF in the ctl file be even easier (though I’ll admit the maskout is way more flexible and necessary if you have a bunch of different variables that each use different missing values).
> 
>  
> 
> From: gradsusr-bounces at gradsusr.org [mailto:gradsusr-bounces at gradsusr.org] On Behalf Of Jeff Duda
> Sent: October 30, 2015 9:46 AM
> To: GrADS Users Forum
> Subject: Re: [gradsusr] Setting missing values (or any value) to undefined
> 
>  
> 
> maskout(WC,WC+119.9)
> 
>  
> 
> On Fri, Oct 30, 2015 at 10:06 AM, Matt Bunkers - WFO UNR <matthew.bunkers at noaa.gov> wrote:
> 
> Hi,
> 
>  
> 
> I have hourly wind chill (WC) grids for which I want to find the minimum WC.  The problem I have is that some of the areas of the grids are missing (set to -120).  When I compute the minimum WC and then display the result (as either image or contour) I get huge gradients between the real data and the missing data.  What I would like to do is set my missing data to undefined (so they don't plot).  I've tried that with the const function but that doesn't appear to work.  Is there another function that would allow me to set a given value (-120 in this case) of my grid to undefined?  If it is set to undefined then when I plot the grid I shouldn't see those horrendous gradients.
> 
> 
> Thanks,
> 
>  
> 
> -- Matt
> 
>  
> 
> 
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> 
> 
> --
> 
> Jeff Duda
> Graduate research assistant
> University of Oklahoma School of Meteorology
> Center for Analysis and Prediction of Storms
> 
> 
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--
Jennifer M. Adams
Center for Ocean-Land-Atmosphere Studies (COLA)
111 Research Hall, Mail Stop 2B3
George Mason University
4400 University Drive
Fairfax, VA 22030 





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