[ncl-talk] Opendap retrieve only a subset of data

[Rick Brownrigg]

Hi Ugo,

Apologies for the delay in reply.  I don't know the issue for certain, but
I think the query syntax should something more like this:

"
http://nomads.ncep.noaa.gov:9090/dods/gfs_0p25/gfs20160701/gfs_0p25_00z?lon[9],lat[40],tmp2m[0:80][40][9]

This seemed to work for me -- I got the time-series at the point 40N, 9E.
What I could not do was use wild-card notation for specifying I wanted all
times, e.g.,    tmp2m[:][40][9].   The syntax seems to accept only explicit
single-values, or a start:stop pair,  or a start:stop:stride tuplet.   That
means I had to look at the metadata of the source file first to know how
many time values were present -- a nuisance at best and a potential source
of error at worst.

I hope that helps...
Rick


On Sat, Jul 2, 2016 at 3:50 AM, Ugo Merlini <umerlini at enet.it> wrote:

> Hi
>
> Sorry I forgot to say I have the opendap version installed also forgot to
> say that this string only retrieve the variables list after the question
> mark for example this line retrive lon, lat and tmp2m variables
>
>
> http://nomads.ncep.noaa.gov:9090/dods/gfs_0p25/gfs20160701/gfs_0p25_00z?lon
> [9],lat[40],tmp2m
> but it grab all tmp2m all over the world when I'm interestest to tmp2m at
> logitude 9 and latitude 40
>
> I have many variables to download at the same position so a subregion
> limitation will save time
>
> Ugo
>
>
> Il 01/07/2016 23:37, Rick Brownrigg ha scritto:
>
> Hi,
>
> Are you getting the "Either file doesn't exist, or NCL does not have
> OPeNDAP capabilities on this system"  message, or some other error -- I'm
> getting a SEGV out of the isfilepresent() function call.   Ncl is
> optionally built with OpenDAP, and it may be that your version was built
> without it?
>
> Rick
>
>
> On Fri, Jul 1, 2016 at 1:03 PM, Ugo Merlini <umerlini at enet.it> wrote:
>
>> I'm trying to to retrieve form ncep opendap server asubset of data
>> limiting the usage of the internet band speed up all the script.  In
>> Grads and in NCO is possibile (but this last give me many reading error)
>> is there a way to it in NCL?
>>
>> Regards
>> Ugo
>>
>> here my script
>>
>> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"
>> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_csm.ncl"
>> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl"
>> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/shea_util.ncl"
>> load "$NCARG_ROOT/lib/ncarg/nclscripts/contrib/calendar_decode2.ncl"
>> load "$NCARG_ROOT/lib/ncarg/nclscripts/contrib/ut_string.ncl"
>>
>> begin
>>    data_sistema =systemfunc("date -d '-1 day' +'%Y%m%d'")
>>
>>    http1 = "http://nomads.ncep.noaa.gov:9090/dods/gfs_0p25/gfs"
>>    http2 = systemfunc("date -d '-1 day' +'%Y%m%d'")
>>    http3 = "gfs_0p25"
>>
>>
>>        filename = http1 + http2 + "/" + http3 + "_00z"
>>        data_run_temp = data_sistema + " 0000"
>>        data_run = systemfunc( "date -u -d '"+ data_run_temp +"' '+%s'" )
>>        run = "gfs_0p25_00"
>>        print(filename)
>>
>>
>>
>>      exists = isfilepresent(filename)
>>      if(.not.exists) then
>>        print("OPeNDAP isfilepresent test unsuccessful.")
>>        print("Either file doesn't exist, or NCL does not have OPeNDAP
>> capabilities on this system")
>>      else
>>        print("OPeNDAP isfilepresent test successful.")
>>        gfs = addfile(filename,"r")
>>        vars = getfilevarnames(gfs)
>>      end if
>>
>> end
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