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Don/Ryan,
Thanks for your response. I suppose I was not clear on my
question. All other doubts have been resolved except this one.
I am wanting to download a subset of the May 2014 file for air temperature
programmatically(either python or java) and I would like to store this file
as a netcdf file on my disk that will be read downstream by a Fortran
program. The URL Ryan gave me will give ASCII file but I am wanting netcdf
binary format. Regarding the URL Don gave me would it be possible to
construct an OpenDap constraint expression and then send it to the RAMADDA
server ?
This is the only outstanding question.
Regards,
Ashwin.
On Fri, May 27, 2016 at 12:57 AM, Don Murray (NOAA Affiliate) <
don.murray@xxxxxxxx> wrote:
> Ashwin-
>
> We do not expose the netCDF subset service (NCSS) on the PSD THREDDS
> server, but the same files can be accessed through the PSD RAMADDA server,
> starting from here:
>
>
> http://www.esrl.noaa.gov/psd/repository/entry/show?entryid=e570c8f9-ec09-4e89-93b4-babd5651e7a9
>
> If you drill down to the 2014 file, you'll get to here:
>
>
> http://www.esrl.noaa.gov/psd/repository/entry/show?entryid=synth%3Ae570c8f9-ec09-4e89-93b4-babd5651e7a9%3AL25jZXAucmVhbmFseXNpczIvcHJlc3N1cmUvYWlyLjIwMTQubmM%3D
>
> where you can download the entire file, or select the "Subset Grid" option
> on the right side of the page. There you can subset by time, level and
> region. (however, you can't pick specific hours, just a range in this
> interface).
>
> For for month of May 2014, latitude between 5 N
> and 40 N and longitude 65 E and 100 E for the pressure level
> 850 hPa, the URL would be:
>
>
> http://www.esrl.noaa.gov/psd/repository/entry/show/air.2014_subset.nc?submit=Subset&output=data.gridsubset&entryid=synth%3Ae570c8f9-ec09-4e89-93b4-babd5651e7a9%3AL25jZXAucmVhbmFseXNpczIvcHJlc3N1cmUvYWlyLjIwMTQubmM%3D&hstride=1&area_north=40&area_west=65&area_east=100&area_south=5&calendar=gregorian&fromdate=2014-05-01%2000%3A00%3A00%20UTC&todate=2014-05-31%2018%3A00%3A00%20UTC&addlatlon=true&level=2&variable=air
>
> (shown at the bottom of the Grid Subset form).
>
> Don Murray
> --
> Don Murray
> NOAA/ESRL/PSD and CU-CIRES
> 303-497-3596
> http://www.esrl.noaa.gov/psd/people/don.murray/
>
> On 5/26/16 12:32 PM, Ryan May wrote:
>
>> Regarding #2, the URL from thredds to just download the file would be:
>>
>>
>> http://www.esrl.noaa.gov/psd/thredds/dodsC/Datasets/ncep.reanalysis2/pressure/air.2014.nc.ascii?air[480:603][2][20:34][26:40]
>>
>> You can find that in the catalog here:
>>
>>
>> http://www.esrl.noaa.gov/psd/thredds/catalog/Datasets/ncep.reanalysis2/pressure/catalog.html?dataset=Datasets/ncep.reanalysis2/pressure/air.2014.nc
>>
>> (The HTTPServer link.)
>>
>> Ryan
>>
>>
>> On Thu, May 26, 2016 at 11:10 AM, ashwinD12 . <winash12@xxxxxxxxx
>> <mailto:winash12@xxxxxxxxx>> wrote:
>>
>> James,
>> What an OpenDap primer from the person who invented
>> OpenDap ! Thank you very much indeed. I absorbed all of that
>> information.
>>
>> I had three more follow up questions(maybe related)
>> 1) I presume this URL relates to air temperatures -
>>
>> http://www.esrl.noaa.gov/psd/thredds/dodsC/Datasets/ncep.reanalysis2/pressure/air.2014.nc.ascii?air[480:603][2][20:34][26:40]
>>
>> Why are the values negative ?
>>
>> 2) I presume I can download this file as a netcdf file in Python or
>> Java ?
>>
>> 3) Finally is there a way in the constraint expression that I can
>> add what time of day I want(00,06,12,18) ?
>>
>> Regards,
>> Ashwin.
>>
>> On Thu, May 26, 2016 at 8:41 PM, James Gallagher
>> <jgallagher@xxxxxxxxxxx <mailto:jgallagher@xxxxxxxxxxx>> wrote:
>>
>>
>>
>> On May 26, 2016 at 07:06:38, ashwinD12 . (winash12@xxxxxxxxx
>> <mailto:winash12@xxxxxxxxx>) wrote:
>>
>> Hello,
>>> I am not sure whether I will get any help for
>>> asking such a basic question on OpenDAP constraint expression
>>> but if this is not the forum for getting clarifications on
>>> OpenDAP constraint expression please let me know the
>>> appropriate forum.
>>>
>>>
>>> I I have this URL
>>> -
>>> http://www.esrl.noaa.gov/psd/thredds/dodsC/Datasets/ncep.reanalysis2/pressure/air.2014.nc.ascii?air[408:603][2][20:34][26:40]
>>> '
>>>
>>>
>>>
>>> This is the output of a program that fetches data from a
>>> THREDDS server. I am wanting to replicate the functionality by
>>> coming up with that URL myself.
>>>
>>> Can somebody explain to me what the values in parenthesis are ?
>>>
>>> This is the input I give
>>>
>>> variable='air',level=850,
>>> months.minmax=c(5,5), years.minmax=c(2014,2014),
>>> lat.southnorth=c(5, 40), lon.westeast=c(65, 100),
>>>
>>> I am wanting data for month of May 2014, latitude between 5 N
>>> and 40 N and longitude 65 E and 100 E for the pressure level
>>> 850 hPa.
>>>
>>> How does that input get translated to the above URL ?
>>>
>>
>> Here’s how the URL breaks down: air.2014.nc .ascii ? air
>> [408:603 ] [2] [20:34] [26:40]
>> <
>> http://www.esrl.noaa.gov/psd/thredds/dodsC/Datasets/ncep.reanalysis2/pressure/air.2014.nc.ascii?air[408:603][2][20:34][26:40]
>> >
>>
>> The dataset (which is a file in this case) is ‘air.2014.nc
>> <http://air.2014.nc>’. You’re asking the server to subset that
>>
>> dataset and return just the variable ‘air’ and to translate the
>> result into ASCII (text). When the variable ‘air’ is extracted
>> from the data set its a four-dimensional array and you’re asking
>> to have those dimensions ‘sliced’ (or subset) so that, for the
>> first dimension, you see only elements 408 to 603, for the
>> second dim only element 2, for the third elements 20 to 34 and
>> elements 26 to 40 for the fourth.
>>
>> You can look at the dataset to see how your request (level=850,
>> …) translated into those array indices by looking at the
>> datasets’s metadata. To do that, removed the .ascii and replace
>> it with .dds, .das and/or .info and don’t include the query
>> string (the part after the ‘?’). Like this:
>>
>>
>> http://www.esrl.noaa.gov/psd/thredds/dodsC/Datasets/ncep.reanalysis2/pressure/air.2014.nc.dds
>>
>> Dataset {
>> Float32 level[level = 17];
>> Float32 lat[lat = 73];
>> Float32 lon[lon = 144];
>> Float64 time[time = 1460];
>> Grid {
>> ARRAY:
>> Int16 air[time = 1460][level = 17][lat = 73][lon = 144];
>> MAPS:
>> Float64 time[time = 1460];
>> Float32 level[level = 17];
>> Float32 lat[lat = 73];
>> Float32 lon[lon = 144];
>> } air;
>> } Datasets/ncep.reanalysis2/pressure/air.2014.nc <
>> http://air.2014.nc>;
>>
>>
>> One thing you’ll see is that ‘air’ is a Grid - so it’s not
>> really a simple array, but rather a collection of arrays: air,
>> time, level, lat and lon. The ‘air’ array holds the data while
>> the other four hold what could be described as the independent
>> variables (or dimensions).
>>
>> You can see more information about the variables by looking at
>> ‘semantic metadata’ like this:
>>
>>
>> http://www.esrl.noaa.gov/psd/thredds/dodsC/Datasets/ncep.reanalysis2/pressure/air.2014.nc.das
>>
>> Attributes {
>> level {
>> String units "millibar";
>> Float32 actual_range 1000.0, 10.0;
>> String long_name "Level";
>> String positive "down";
>>
>> …
>>
>> Hope this helps,
>> James
>>
>>
>>>
>>>
>>> Regards,
>>> Ashwin.
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>>
>> --
>> James Gallagher
>> jgallagher@xxxxxxxxxxx <mailto:jgallagher@xxxxxxxxxxx>
>>
>>
>>
>> _______________________________________________
>> NOTE: All exchanges posted to Unidata maintained email lists are
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>>
>>
>>
>>
>> --
>> Ryan May, Ph.D.
>> Software Engineer
>> UCAR/Unidata
>> Boulder, CO
>>
>>
>> _______________________________________________
>> NOTE: All exchanges posted to Unidata maintained email lists are
>> recorded in the Unidata inquiry tracking system and made publicly
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