[gradsusr] semi-advanced ave tool use

[Jennifer Adams]

This is related to the recent thread on comparing defined variables  
independent of their time metadata. You must create a new data set and  
override the lat/lon metadata in the subsets you create.

Just for the sake of argument, and to be sure I've understood your  
question correctly, let's say you're looking at precip patterns around  
a hurricane and want to have the hurricane center be at the center of  
your grid for each time step and so the lat/lon values of the grid  
change with each new time step. I assume the grid size is the same for  
each time (i.e. the lat/lon increments don't change). Then,
1. locate the grid point that contains the hurricane center
2. use fwrite to write out a lat/lon grid that is centered on that  
grid point, let's say your grid has 101 points in the X and Y  
directions.
3. go to the next time step and repeat steps 1 and 2 until you've  
written out the number of grids of interest, say it's 48
4. write a descriptor file that contains the following entries:

xdef 101 linear -50 1
ydef 101 linear -50 1
tdef 48 linear <initial_time> <time_increment>

When you look at this data in GrADS, be sure to 'set mproj off' and  
then it won't try to map your grids to world coordinates, X and Y will  
just be abstract coordinates, and (0,0)  will always be the location  
of the center of the hurricane. Then you can do whatever analysis you  
want without worrying that your grids are not co-located in lat/lon  
space. You could animate over time and see blobs of precip rotating  
around the center of your grid. Is that what you need?

--Jennifer




On Jul 19, 2011, at 4:36 PM, Rowell, Mason D. wrote:

> Hello Grads community,
>
> I can see from the tutorial that one can open several different case  
> files in grads(file1, file2 etc) and average the data from these  
> files for subsequent display. Is there an advanced option that would  
> allow me to specify the domain for each case and then average them?  
> I was hoping to use this function to easily complete an average of  
> 25 cases or so but relative to some specific type of event, which  
> requires different domain centering for each case prior to averaging.
>
> Mason
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--
Jennifer M. Adams
IGES/COLA
4041 Powder Mill Road, Suite 302
Calverton, MD 20705
jma at cola.iges.org



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