Hi Ashwin- On 5/26/16 7:12 PM, ashwinD12 . wrote:
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 ?
The subset URL I sent will return a netCDF file. You can replace certain parameters in the url arguments for different levels and regions and times, or replace the entry id with that of another file on the server. You can use the pycurl module in Python to retrieve the file using that URL. The subset from that URL is attached.
You could also use the netcdf-java library to make the subsets programmatically in Java, pointing to the OPeNDAP URL. You can do the subsets in real world space (e.g. lat/lon, time (with a stride), etc) and it will convert that to the appropriate index space constraints.
You cannot use the constraint expressions with netcdf-java or through the RAMADDA url (which in the end calls the netcdf-java library). I'm not sure why you would need that when you can use a higher level interface.
Don
This is the only outstanding question. Regards, Ashwin. On Fri, May 27, 2016 at 12:57 AM, Don Murray (NOAA Affiliate) <don.murray@xxxxxxxx <mailto: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> <mailto: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> <mailto:jgallagher@xxxxxxxxxxx <mailto:jgallagher@xxxxxxxxxxx>>> wrote: On May 26, 2016 at 07:06:38, ashwinD12 . (winash12@xxxxxxxxx <mailto:winash12@xxxxxxxxx> <mailto: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 <http://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> <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> <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. _______________________________________________ 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 <mailto:thredds@xxxxxxxxxxxxxxxx> <mailto:thredds@xxxxxxxxxxxxxxxx <mailto:thredds@xxxxxxxxxxxxxxxx>> For list information or to unsubscribe, visit: http://www.unidata.ucar.edu/mailing_lists/ -- James Gallagher jgallagher@xxxxxxxxxxx <mailto:jgallagher@xxxxxxxxxxx> <mailto:jgallagher@xxxxxxxxxxx <mailto: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 <mailto:thredds@xxxxxxxxxxxxxxxx> <mailto:thredds@xxxxxxxxxxxxxxxx <mailto: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 _______________________________________________ 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 <mailto:thredds@xxxxxxxxxxxxxxxx> For list information or to unsubscribe, visit: http://www.unidata.ucar.edu/mailing_lists/
-- Don Murray NOAA/ESRL/PSD and CIRES 303-497-3596 http://www.esrl.noaa.gov/psd/people/don.murray/
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