Re: New Ticket - [THREDDS !HWQ-525500]: Re: [support] About NEX data download options

Greetings Sayli,

Using OPeNDAP to get ascii data is very difficult, not to mention that there is a 50 MB limit when returning ASCII via OPeNDAP - your request would take GBs of data. Thankfully, the server you are using to access data from supports the netCDF Subset Service, which allows you to make requests of data using the lat/lon/time bounds you are interested in obtaining data for without figuring out the correct array indicies. The downside is that for gridded data (like model output), you will get a netCDF file back in return (only a downside if you need ascii data). However, there are several tutorials on how to convert a netCDF file into ascii, so that part should not be too bad. A good place to start would be the netCDF FAQ:

http://www.unidata.ucar.edu/software/netcdf/docs_rc/ncFAQ.html#How-do-I-convert-netCDF-data-to-ASCII-or-text

Now, back to getting the data! To use the Netcdf Subset Service, I would first recommend going to the main dataset THREDDS catalog page, found here:

http://dataserver3.nccs.nasa.gov/thredds/catalog/bypass/NEX-GDDP/bcsd/historical/r1i1p1/tasmin/catalog.html?dataset=bypass/NEX-GDDP/bcsd/historical/r1i1p1/tasmin/inmcm4.ncml

Under the Access heading, look for the NetcdfSubset link. If you click that, you will be taken to this page:

http://dataserver3.nccs.nasa.gov/thredds/ncss/grid/bypass/NEX-GDDP/bcsd/historical/r1i1p1/tasmin/inmcm4.ncml/dataset.html

Here you will be able to enter your lat/lon bounding box into some text boxes (make sure to uncheck the "disable horizontal subsetting"), as well as the date/time range you are interested in. As you enter information on the page, you should note that a URL is being built at the bottom of the page. This URL is what you can use directly to get the netCDF file.

Note that your full request is too big for the server to fulfill in one shot - you will need to request data in 5 year intervals. The URL for the first 5 years looks like this:

http://dataserver3.nccs.nasa.gov/thredds/ncss/bypass/NEX-GDDP/bcsd/historical/r1i1p1/tasmin/inmcm4.ncml?var=tasmin&north=33.5&west=66.5&east=100&south=6.5&disableProjSubset=on&horizStride=1&time_start=1950-01-01T12:00:00Z&time_end=1955-12-31T12:00:00Z&timeStride=1

It does take some time for the server to fulfill the request, so patience will be needed. Once you get the file, I would rename to something meaningful and then request the next 5 years worth of data by simply editing the time range in the URL. Note that 5 years worth of data is roughly 125 MB, and this will expand substantially when you extract the data from the netCDF file to ascii...this is one of the many reasons that it is recommended to just use the netCDF file rather than going to ascii.

Best of luck!

Sean

On Thu, Feb 18, 2016 at 4:36 PM, Sayli Tawde <address@hidden> wrote:

New Ticket: Re: [support] About NEX data download options


Sayli,
I'm forwarding this to Unidata's support email, they are
the makers of that server and can help you.

Goood luck,

James


On February 17, 2016 at 03:34:19, सायली तावडे (address@hidden) wrote:

Hello sir/ madam

I am a PhD student at Indian Institute of Science (IISc), Bangalore, India.
My research is on glaciers and their response to climate change.

I want to download the NEX data for India containing all models-historical
data (Tmin, Tmax, PR) for 6.5 to 33.5 N latitude and 66.5 to 100E longitude.
I was trying to get ASCII files from following server

http://dataserver3.nccs.nasa.gov/thredds/dodsC/bypass/NEX-GDDP/bcsd/historical/r1i1p1/tasmin/inmcm4.ncml.html

However, I am not able to download the data for all the 56 years (1950 to
2005) at a time. Is there any way to get this ASCII files at a time for
all 56 years or in the interval of 10 years? It will be very useful for
me to save my huge amount of time of research.

Thanking you in advance.

Sincerely
Sayli Tawde
PhD,
Centre for Atmospheric and Oceanic Sciences,
IISc, India

--
James Gallagher
address@hidden


Ticket Details
===================
Ticket ID: HWQ-525500
Department: Support THREDDS
Priority: Normal
Status: Open
Link:  https://andy.unidata.ucar.edu/esupport/staff/index.php?_m=tickets&_a=viewticket&ticketid=26692