[thredds] Thredds Opendap Dataset Access Form "Get as NetCDF"

Hi all,

Thanks for the earlier replies.

I was looking at the OPeNDAP Server Dataset Access Form 
(http://test.opendap.org/opendap/data/nc/sst.mnmean.nc.gz.html) and under 
Action, there's a "Get as NetCDF" option in this form, however the Thredds 
instance I have deployed do not have this option. 

Under the General Help it reads:
To get data in ASCII, various common formats or DODS binary objects, click on 
one of the buttons labeled Get .... The Get ASCII and Get DODS Data Object 
buttons will always be present. Other buttons may be present providing access 
other types of return formats such as NetCDF, HDF, et cetera. Note that in 
order to use the DODS Data Objects, you'll need to download software from the 
OPeNDAP web site to decode them.

How do I go about enabling this option? I am interested in being able to 
download the subsetted datasets as Netcdf files.


Thank you for your time.


Regards,

Derrick Wong 
Software Engineer | ASRDC (Australian Spatial Research Data Commons) Project | 
CSIRO

Phone: +61 8 6436 8945
derrick.wong@xxxxxxxx | www.csiro.au
Address: ARRC (Australian Resources Research Centre), 26 Dick Perry Avenue, 
Kensington WA 6151, Australia


-----Original Message-----
From: Roy Mendelssohn [mailto:Roy.Mendelssohn@xxxxxxxx] 
Sent: Wednesday, 21 July 2010 10:37 PM
To: Wong, Derrick (CESRE, Kensington)
Cc: thredds@xxxxxxxxxxxxxxxx
Subject: Re: [thredds] Thredds Opendap request

Relational constraint expressions do no work for grids in OpeNDAP.  You have to 
constrain based on the range of indices in the grid.  If you go to the OPeNDAP 
html page it will help guide you to perform a subset.  For example from one of 
the datasets my group serves:

http://oceanwatch.pfeg.noaa.gov/thredds/dodsC/satellite/BA/ssta/mday.html

to get the first time period, the first 30 lats and 50 lons the constraitn 
would be:

http://oceanwatch.pfeg.noaa.gov/thredds/dodsC/satellite/BA/ssta/mday?BAssta[0:1:0][0:1:0][0:1:29][0:1:49]

HTH,

-Roy 
On Jul 21, 2010, at 12:01 AM, Derrick.Wong@xxxxxxxx wrote:

> Hi all,
> 
> I have set up a TDS (Version 4.1.20100520.1554 - 20100520.1554) and I am 
> having some problem requesting for data using the built-in OPeNDAP service.
> 
> I am trying to subset the dataset based on a spatial extent (bbox), and in 
> the opendap documentation, it is mentioned that this is possible if you 
> specify a constraint in your request. 
> (http://opendap.org/user/guide-html/guide_34.html#id6)
> 
> I am getting the following error when I try to make a simple query 
> http://apacsrv6/thredds/dodsC/bom/mslp.2009043000.nc.ascii?mslp&lat>15.0 :
> 
> Error {
>    code = 2;
>    message = "The variable `15' was not found in the dataset.";
> };
> 
> 
> 
> My Dataset is as follows:
> 
> Dataset {
>    Float32 lat[lat = 480];
>    Float32 lon[lon = 600];
>    Int32 tm_step_size;
>    Int32 base_date;
>    Int32 base_time;
>    Int32 valid_date[time = 1];
>    Int32 valid_time[time = 1];
>    String seg_type[time = 1];
>    Float32 mslp[time = 1][lat = 480][lon = 600];
> } bom/mslp.2009043000.nc;
> ---------------------------------------------
> lat[480]
> -55.0, -54.875, -54.75, -54.625, .......
> 
> lon[600]
> 95.0, 95.125, 95.25, 95.375, 95.5, ......
> 
> tm_step_size, 240
> base_date, 20090430
> base_time, 0
> valid_date[1]
> 20090430
> 
> valid_time[1]
> 0
> 
> seg_type[1]
> "FORC"
> 
> mslp[1][480][600]
> 
> [0][0], 983.6426, 983.6654, 983.6847, 983.7006, ....
> [0][1], ....
> .....
> 
> 
> 
> I have noted that the syntax of the OPeNDAP request within thredds is a bit 
> different, could someone kindly assist?
> 
> Thank you for your time.
> 
> Regards,
> 
> 
> Derrick Wong 
> Software Engineer | ASRDC (Australian Spatial Research Data Commons) Project 
> | CSIRO
> 
> Phone: +61 8 6436 8945
> derrick.wong@xxxxxxxx | www.csiro.au
> Address: ARRC (Australian Resources Research Centre), 26 Dick Perry Avenue, 
> Kensington WA 6151, Australia
> 
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**********************
"The contents of this message do not reflect any position of the U.S. 
Government or NOAA."
**********************
Roy Mendelssohn
Supervisory Operations Research Analyst
NOAA/NMFS
Environmental Research Division
Southwest Fisheries Science Center
1352 Lighthouse Avenue
Pacific Grove, CA 93950-2097

e-mail: Roy.Mendelssohn@xxxxxxxx (Note new e-mail address)
voice: (831)-648-9029
fax: (831)-648-8440
www: http://www.pfeg.noaa.gov/

"Old age and treachery will overcome youth and skill."
"From those who have been given much, much will be expected"

-----Original Message-----
From: Daniel Holloway [mailto:d.holloway@xxxxxxxxxxx] 
Sent: Wednesday, 21 July 2010 9:59 PM
To: Wong, Derrick (CESRE, Kensington)
Cc: thredds@xxxxxxxxxxxxxxxx; support@xxxxxxxxxxx support
Subject: Re: [thredds] Thredds Opendap request

Derrick,

     The documentation you're referencing shows how to make constraint  
expressions to both 'sequence' containers, and 'arrays and grids'.    
The selection operation you're using is only applicable to 'sequences'  
and not 'arrays and grids' (at least not currently though value-based  
array selection is often a requested capability for the DAP).

     To accomplish your goal you would need to retrieve the 'lat'  
variable first to determine the indices in the value range you're  
looking for (.i.e., lat > 15)

     then you could constrain the 'mslp' variable accordingly, like so:

    http://www.apacsrv6/thredds/dodsC/bom/mslp.2009043000.nc.asc? 
mslp[0][355:479][0:599]

    the above assumes that 'lat' values greater than '15' reside in  
the indices [355 to 479] (the top of the lat dimension), and you want  
all the 'lon' coverage.

    Dan