[gradsusr] Speed optimizations

[Travis Wilson - NOAA Federal]

Hi,


At the NWS we have been using grads to create images from grib files on the
fly.  Users use a front end interface to select a model (which is just a
grib file on a server), field, and view, and submits a job.  Within 3-4
seconds the server is able to launch grads, open the grib file, and produce
50-100 images for the user to view.  This works extremely well for CONUS
datasets with medium to coarse resolutions (up to 6km).

We have started using higher resolution grib files (1 km radar files are
attached) and they are substantially slower.  The main problem comes from
opening the file.  If a user selects radar for Northern California, it
takes grads approximately 18 seconds just to open the 1km CONUS radar file
(scanning descriptor file)..and then grads plots rather quickly.


A workaround we have been using is to subset the data on the fly (since we
don’t know the area the user will select).  This example regrids the CONUS
radar for northern California.


wgrib2 1kmradar_201512241600.grib2 -small_grib 233:243 36.8:42.8
1kmradar_201512241600.grib2.small


The small grib file will open in GrADS in about 1 second.  Regridding, and
remaking the ctl and idx is substantially faster, but still requires a lot
of time.  My question is, is there any way to speed up the scanning of the
CONUS descriptor file without subset the grib file.  For example, grads
would not scan the entire conus descriptor file when we just need to look
at Northern California (or whatever portion of the US the users selects).


We appreciate all the help,

Travis
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