Re: Web service for Total Precipitation

• To: Ernest To <ernesto_24_7_365@xxxxxxxxx>
• Subject: Re: Web service for Total Precipitation
• From: John Caron <caron@xxxxxxxxxxxxxxxx>
• Date: Sat, 25 Mar 2006 19:21:31 -0700

Hi Ernest:

Ernest To wrote:

John,

My name is Ernest To and I am a student of Dr.
Maidment's.  Tim Whiteaker and I are trying to write a
webservice that would download total precipitation
data for the continental US at resolution of 20km from
unidata website for a given time and place.  We have
so far been experimenting with the following link:

http://motherlode.ucar.edu:8080/thredds/dodsC/model/NCEP/NAM/CONUS_20km/surface/NAM_CONUS_20km_surface_20060324_1800.grib1.html

Can we ask you the following questions?
1.  What is a .grib1 or a .grib2 file?  Is it in
netcdf format?

no, grib1 and grib2 are WMO formats for gridded data

2.  We noticed that in the link above (OPENDAP ) there
are options for getting a binary file or an ASCII
file.  Are those files in netcdf and cdl formats
respectively?

no, they are in opendap specific formats. normally you would use the opendap 
client library (C++ or Java) to access data through opendap, rather than 
downloading files.

3.  Our webservice requires the creation of a URL
query based on user inputs (such as coordinates of
bounding rectangle, time period of interest and
parameter of interest) which will then be used to
request data from the website.  Could you provide
information on how to convert geographical coordinates
(in decimal degrees) and time values (MM/DD/YYYY
hh:mm) into the array indices shown in the website

above? e.g. time[0:1:0] y[0:1:0] x[0:1:0]

this is not trivial, as it depends on the specific file. there are routines in 
the netcdf-java 2.2 library that can do it. Are you using java?

what file formats can you handle? what does your web service do?

  Thank you for your kind attention.  Please let me
know if anything is unclear.  I can be reached either
by e-mail: ernesto_24_7_365@xxxxxxxxx or by phone:
512-508-4834.

  Thanks.

Ernest To
PhD student
Center for Research in Water Resources
University of Texas at Austin
512-508-4834

--- John Caron <caron@xxxxxxxxxxxxxxxx> wrote:

Hi David, Ernest:

Have a look at the motherlode catalog:

 http://motherlode.ucar.edu:8080/thredds/

we were guessing you will want the NAM 21-km
dataset?

If you want to use WCS protocol, you can get back
geotiff or netcdf-CF. Otherwise you could use
Opendap.

There's a few other wrinkles concerning time
dimension, we can go over.

David Maidment wrote:

Ernest:

Please see the message below from Mohan Ramamurthy

at Unidata.  Can you

please work with John Caron
to see how we can ingest a field using web

services.  I'd like to stick

to something 2D on the land surface like precipitation, evaporation or soil

moisture.  I believe

those are all in the eta model
output.   Likely what we want to do is to give a

lat-long box, a time

point and a variable, and ask
for a field over the region of the lat-long box

for that variable and

time point, and it might occur
that the field actually covers several forecast

intervals, eg. 3 hour

forecast times for a day.  I'm
not sure in that case if we should treat each time

slice as one field in

the web services ingest, but
lets look into what is involved and then figure

out what is best.

John -- I'd like to see what can be done with a

WCS service if possible.

Thanks for your help.

David


-----Original Message-----

From: Mohan Ramamurthy [mailto:mohan@xxxxxxxx] Sent: Friday, March 10, 2006 5:40 PM

To: David Maidment
Cc: John Caron; Mohan Ramamurthy
Subject: Web service to Operational Eta model

output

David,

I just spoke to John Caron

(caron@xxxxxxxxxxxxxxxx), our lead developer

on THREDDS, re. our conversation this afternoon to

create a web service

to access fields from the operational model output

in the IDD stream.

John will be happy to work the person on your to

make it happen.  It

looks like many of the pieces are already in place

to enable a web

service for accessing, subsetting, and moving

individual fields, because

the data is served via OPeNDAP.  For example, here

is the OPeNDAP URL

for today's Eta output:

http://motherlode.ucar.edu:8080/thredds/dodsC/model/NCEP/NAM/Alaska_22km

/NAM_Alaska_22km_20060310_1200.grib1

By the way, John also has an experimental WCS

server that provides the

same data via the WCS interface.

I will let John and your technical developer to

work out the details on

how to make this happen, but it looks

straightforward and doable based

on my discussions with John.

Mohan

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