[gradsusr] Using subsetting on a grads data server

[Shaun Carney]

Hello,
I have what hopefully is a simple question. I'm trying to do a clip of
a precip grid to a small area on a grads server rather than opening
the entire dataset and then doing the clip. The following works:

'sdfopen http://nomads.ncep.noaa.gov:9090/dods/nam/nam20110808/nam_crb_00z'
'set lon 269 273'
'set lat 12 15'
'set t 1 29'
'define namprecip = apcpsfc'

However, when I try to give an expression so that I only get the
subset from the server, it will not work:

baseurl    = 'http://nomads.ncep.noaa.gov:9090/dods/nam/_expr_'
datasets   = '{nam20110808/nam_crb_00z}'
expression = '{apcpsfc}'
dimensions = '{269:273,12:15,1000:1000,00Z08AUG2011:12Z11AUG2011}'
'sdfopen '%baseurl%datasets%expression%dimensions
'set t 1 29'
'define namprecip = result'

Grads gives the following error:
gadsdf: Couldn't ingest SDF metadata

Any ideas why this will not read? On a more basic level, will there be
any speed improvement using the second method rather than the first,
or does setting the coord box before defining namprecip reduce the
data transfer?

This will be implemented on a computer with slow connection speed so I
want to minimize data transfer.

Thanks!
Shaun