Overlay different resolution grids using OpenGrADS re()

Arlindo da Silva dasilva at ALUM.MIT.EDU
Sun Jun 22 12:03:17 EDT 2008

On Fri, Jun 20, 2008 at 9:32 PM, Mike Johnson <mike.w.johnson at noaa.gov>

> Users, Can anyone help with what I suspect is either a regrid problem
> (using re.gex) - or - in the methodology I'm using for output fwrite - or -
> an issue with my understanding of how options yrev works.

This shouldn't be an issue in this case. Usually, when you misuse yrev you
end up with an upside down plot, something easy to diagnose.

> I am attempting
> to regrid a subdomain of a large regional netcdf topo file
> (US_Rockies_GLOBE_30sec_topo.nc resolution - 30 Sec resolution) and write
> that regridded subdomain to a binary file (Idaho.dat) which I then want to
> overlay with high resolution surface wind field from CALMET (0.25km
> resolution).
> My basic procedure is to (1) convert grid spacing for control files and re
> () to DeltaX and DeltaY in degrees; (2) select a subdomain of the large
> NetCDF TOPO file (US_Rockies_GLOBE_30sec_topo.nc) which has Y dims written
> from north-to-south and (3) to regrid this smaller domain using re() in
> order to match domain size and dimensions of CALMET surface wind field; and
> (4) write a binary file (Idaho.dat) which I'm hoping to overlay with the
> CALMET wind data (and future runs of this model over the same domain).
> I am able to open large domain TOPO file (US_Rockies_GLOBE_30sec_topo.nc),
> regrid to higher resolution and plot subdomain. However...after writing
> this re-gridded subdomain file to binary output (Idaho.dat), when I try to
> plot it using (Idaho.ctl) the file appears to be garbage with GrADS
> echoing "Contouring: 1e+36 to 9e+36" whereas in reality values should be
> something like "1000 to 2800".

Hmm... In your ctl you have

UNDEF -9999.0

are you sure of that? Do you have any UNDEF in your dataset? Make sure re()
is not adding undef at the borders. Here is a couple of things you could do
to further diagnose your problem:

1) Specify the clevs when contouring your data:

ga-> set clevs 1000 1500 2000 2500 3000
ga-> d tpo

2) Examine the min/max of your data:

ga-> set gxout stat
ga-> d tpo


Arlindo da Silva
dasilva at alum.mit.edu
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