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
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Ryan May, Ph.D.
Software Engineer
UCAR/Unidata
Boulder, CO
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