[gradsusr] meteogram data gds/dods efficient data calls

[Jennifer Adams]

On Aug 9, 2011, at 4:27 PM, Howard Staines wrote:

> Meteograms seem to take a long time and data efficiency seems to
> Make the difference between a good and a bad script.
True. That is primarily because of the compression in grib2 files --  
in order to get data for a single grid point, you must first read the  
entire grid from disk, uncompress it, then extract the one data value.  
The meteogram, a set of 1-D time varying plots, forces you to read a  
whole lot more data than you really need, but there is no way around  
that. Meteograms are slow to draw even when reading from local disk.

> I imagine the same is true of skew plots.
>
> With multiple variables what is the efficient way to write the  
> script for
> For server efficiency with dods/gds/opendap type data calls?
The workaround is to create a local binary version of the data you  
want to draw, so that you only need to hit the server once to get the  
data point of interest. From then on, you are reading from your local  
version, and it is much faster. If you are drawing meteograms for more  
than one location, download the smallest possible lat/lon grid that  
will contain all your locations of interest for each variable and time  
step.

Have a look at the scripts I use to draw meteograms at COLA -- they  
are in ftp://iges.org/pub/jma/meteograms/
They are not enabled for opendap access, but have a look at the README  
file and you will get the idea of how to do what you want. I save the  
entire global domain at each time step, but you could limit the lat/ 
lon boundaries (or even just write out a single point) to speed up the  
I/O from the server.

>
> Is the function collect any use for this purpose?
No, that won't help speed things up.

--Jennifer
>
> Regards
>
> Howard Staines
>
>     Metris Limited
>
> phone 0800 372 433 - mobile 027 2785586 - P O Box 5136 Greenmeadows,  
> NAPIER
> email info at metris.co.nz - info at metscape.net.nz - website www.metris.co.nz 
>  -
> www.metscape.net.nz
>
>
>
>
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--
Jennifer M. Adams
IGES/COLA
4041 Powder Mill Road, Suite 302
Calverton, MD 20705
jma at cola.iges.org



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