RE: [ncl-talk] NCL operationally

Hi all,

This is just a follow up on my from January 16 concerning a comparison
of NCL vs. MetView. We've continued the testing and improved quite a lot
the performance NCL. Our benchmark is a script which produces 3 plots
(RH @ 850hPa, T + Geopot. Height @ 850Hpa, ThetaE + Geopot. Height @
850hPa). The equivalent potential temperature is computed from model
variables in the graphics package. We repeat the script 10x and write
output to *.eps in NCL which is afterwards converted to *.png with
convert or pstoimg. MetView can write directly png files and thus the
values for the conversion are missing. The results in seconds are as
follows...

-------------------------------------------
         PS Plot Conversion to png Total
                      convert pstoimg
-------------------------------------------
MetView (46) 50
NCL 28 26 18 46
-------------------------------------------

Several things to note:

- NCL performs badly for reading large (huge) grib files. We've used an
external program to reduce the number of grib records to what we
actually need for plotting.

- As mentioned in one the posts, pstoimg outperforms convert, even
though it is based on ghostscript under the hood. Probably the antialias
is done differently.

- NCL would slow down by a factor of 2-3 if it would also display the
data in a transformed projection. We use the "native grid"
(tfDoNDCOverlay = "NDCDataExtent") method in order to drastically
improve performance. Since MetView is displaying the data in a
Stereographic projection and our model uses a CylindricalEquidistant
projection with a rotated grid, the comparison is not completely fair. I
suppose this is the price we pay for having the option of "on the fly"
transformation of NCARG Graphics the moment the plots are overlaid!

- The experimental PNG driver seems to be very slow (as already noted in
a post) and conversion of *.ps or *.pdf seems to be the way to go.
Nevertheless, I think there is considerable interest in the community to
have fast and efficient *.png output from NCL.

- We will probably start introducing NCL operationally for the first few
plots quite soon... :-)

- I would have liked to try the option of using the NCAR Graphics
Metafile format and conversion to *.png via ctrans. But ctrans does not
seem to be part of my NCL distribution. At least it does not sit in the
$NCARG_ROOT/bin directory along with idt, ncl, and all the rest... Any
ideas?

Thanks for all the posts and help!

Cheers,
Oli

________________________________________

Oliver Fuhrer
Numerical Models

Federal Departement of Home Affairs FDHA
Federal Office of Meteorology and Climatology MeteoSwiss

Kraehbuehlstrasse 58, P.O. Box 514, CH-8044 Zurich, Switzerland

Tel. +41 44 256 93 59
Fax +41 44 256 92 78
oliver.fuhrer_at_meteoswiss.ch
www.meteoswiss.ch - First-hand information
  
 

> -----Original Message-----
> From: ncl-talk-bounces_at_ucar.edu
> [mailto:ncl-talk-bounces_at_ucar.edu] On Behalf Of
> Oliver.Fuhrer_at_meteoswiss.ch
> Sent: Montag, 19. Januar 2009 16:09
> To: ncl-talk_at_ucar.edu
> Subject: NCL operationally
>
> Hi all,
>
> We are currently benchmarking NCL against MetView (from
> ECMWF). The goal would be to use NCL operationally to produce
> plots of our model output. Most of these products are
> produced in time-critical mode.
>
> Currently, there seem to be two bottlenecks that are slowing
> NCL down considerably as compared to MetView. The first is
> the reading of our model output in grib1 format. After
> offline conversion using ncl_convert2nc to NetCDF format and
> execution of the same script simply reading a couple of
> fields from a couple of files, the script runs 10x faster.
> The second is the generation of raster graphics using NCL. A
> lot of our plots are disseminated in PNG or GIF format.
> MetView can directly write these formats whereas NCL writes a
> PS or PDF and the raster format is produced using the
> "convert" utility.
>
> 1) I would be very much interested in future plans for NCL
> concerning these two points.
>
> 2) Would a generation of NCGM and conversion using ctrans to
> a raster format bring any gain in performance?
>
> Thanks and kind regards,
> Oliver
>
>
> ________________________________________
>
> Oliver Fuhrer
> Numerical Models
>
> Federal Departement of Home Affairs FDHA
> Federal Office of Meteorology and Climatology MeteoSwiss
>
> Kraehbuehlstrasse 58, P.O. Box 514, CH-8044 Zurich, Switzerland
>
> Tel. +41 44 256 93 59
> Fax +41 44 256 92 78
> oliver.fuhrer_at_meteoswiss.ch
> www.meteoswiss.ch - First-hand information
>
>
>
>
>
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Received on Thu Jan 22 2009 - 10:12:22 MST