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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> 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> > wrote: > >> >> >> On May 26, 2016 at 07:06:38, ashwinD12 . (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’. 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; >> >> 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. >> _______________________________________________ >> NOTE: All exchanges posted to Unidata maintained email lists are >> recorded in the Unidata inquiry tracking system and made publicly >> available through the web. Users who post to any of the lists we >> maintain are reminded to remove any personal information that they >> do not want to be made public. >> >> >> thredds mailing list >> thredds@xxxxxxxxxxxxxxxx >> For list information or to unsubscribe, visit: >> http://www.unidata.ucar.edu/mailing_lists/ >> >> >> -- >> James Gallagher >> jgallagher@xxxxxxxxxxx >> > > > _______________________________________________ > NOTE: All exchanges posted to Unidata maintained email lists are > recorded in the Unidata inquiry tracking system and made publicly > available through the web. Users who post to any of the lists we > maintain are reminded to remove any personal information that they > do not want to be made public. > > > thredds mailing list > thredds@xxxxxxxxxxxxxxxx > For list information or to unsubscribe, visit: > http://www.unidata.ucar.edu/mailing_lists/ > -- Ryan May, Ph.D. Software Engineer UCAR/Unidata Boulder, CO
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