[gradsusr] Speed optimizations

[Travis Wilson - NOAA Federal]

Hi James,

I converted the file to a netcdf via sdfwrite and you are right.  The file
opens almost instantly.  I wonder why grib files are so slow to open and if
this could be avoided?   It is worth noting that the netcdf file is about
3x larger even with using the -zip option.  Unfortunately since this is an
archive, we can't just increase the data stored by a factor of 3.

I like your idea of the OPenDAP server, we may have to check into this if
there is no other option.





On Thu, Jan 14, 2016 at 4:05 PM, James T. Potemra <jimp at hawaii.edu> wrote:

> Hi Travis,
>
> This seems a little strange to me.  I did a quick test with one of our
> higher res data sets (global bathy) that is 21600 by 64800 (x,y) and it
> loads almost instantly in GrADS.  Of course generating a display takes a
> long time, and my test was done on a netCDF file.
>
> This aside, could you run the data through an OPeNDAP server?  Even though
> it would be on the same machine, you could use the server to subset via the
> DAP call, rather than relying on GrADS to load the entire file.
>
> Jim
>
>
> On 1/14/16 12:54 PM, Travis Wilson - NOAA Federal wrote:
>
> 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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