[gradsusr] Performance Tips

[Wesley Ebisuzaki - NOAA Federal]

Travis,

   I haven't tried this but it may work.

   Instead of regridding your hi-res lat-lon data, make a new control file
which has a PDEF .. BILIN.  This PDEF would map low_res(i,j) -> hi_res(n*i,
n*j)

     low_res() : the low-res x-y grid which is defined in the low-res ctl
file.
     hi_res(): the hi-res grib file grid

I don't remember if grids start at grid(0,0) or grid(1,1).  If grids start
at (1,1) then
the above formula would have to be changed.

Wesley



On Tue, Feb 9, 2016 at 5:37 PM, Travis Wilson - NOAA Federal <
travis.wilson at noaa.gov> wrote:

> Hi All,
>
>
>
> Attached is a very short ppt on grads performance vs python using grib
> files.  In most cases, grads blows python away.  Times are relative to our
> machine and consider everything from starting grads/opening the file, to
> closing the file.
>
>
>
> - In particular we have found that shaded1 is much faster.  Up to 40%
> faster on our machines.
>
> - Wesley Ebisuzaki recommended converting the grib files to a lat/lon grid
> to eliminate the PDEF entry to significantly speed up the opening time of
> high resolution grib files.
> http://gradsusr.org/pipermail/gradsusr/2016-January/039339.html
>
> - Again noted by Wesley, grib packing can have an impact on performance
> http://gradsusr.org/pipermail/gradsusr/2010-May/027683.html
>
>
>
> One thing we show in the ppt is that as the view gets wider (i.e. the
> number of points that are plotted increase), the slower grads is relative
> to python.  At some point, python will become faster.   Anyways, to battle
> with this, regridding (using the re() function) the data within grads
> significantly speeds up the plotting time (see last slide) when you have a
> lot of points.  As far as I know, you can’t use re() in grads 2.1a3.  You
> do have lterp() but a grid is needed.  Is there anything that will allow me
> to lterp to my image dimensions?  Say my image dimensions are x800 y600
> then lterp would interpolate my high resolution grib file to x800 y600 (or
> some multiple of) when a view exceeds 800 points across.  This will
> significantly speed up the plotting time when viewing a wide view of a high
> resolution grib file while not degrading the image quality by much (again,
> see last slide).
>
>
>
> Also, if anyone has other performance tips on plotting high resolution
> grib files we would love to hear them.
>
>
>
> Thanks,
>
> Travis
>
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