Hi Ernest:
We have an experimental web service that will allow you to download the data
that you want in NetCDF format. You will be able to specify the bounding box in
lat/lon, so no need to convert to array indices.
You will need to read the file, using the netcdf C library, and convert to your
format.
It will be ready for you to try in a few days. I can send you a sample of how
the file will look if you want to get started.
Ernest To wrote:
John,
Thanks for your reply. In essence, the purpose of
the webservice is to allow the lay user to submit data
requests in a standardized manner to the unidata
website and to receive data in a format that is usable
on different platforms (e.g. VB.NET, IDL, etc.)
The following is the sequence of steps of the
webservice:
1. accept standardized inputs from the user (i.e. lat
long box, time period, parameter of interest) and
convert them into a URL query for the website
2. submit the URL query to the website and download
the data (the data can be in any format - ASCII or
binary)
3. Process the data into standardized text
format,i.e.:
a. ARCHydro TimeSeries format for one dimensional
arrays, or
b. NetCDF ASCII (.CDL file) format for grids or
multi-dimensional arrays.
4. Incorporate the data text into an XML file and
send it to the user. For visual basic users, Tim has
developed webservicewrappers that would ingest these
XML files into visual basic variables (e.g. sorted
lists) to make it easy for analysis.
Such webservices have been developed for the NWIS,
Ameriflux, MODIS, DAYMET websites, and we would like
to develop one for UNIDATA that would utilize the same
standardized input format.
For this reason, I am very interested in how current
users are querying and subsetting UNIDATA data,
especially in how OPeNDAP works. Perhaps (as a wild
guess), to utilize what already has been done, our
webservice could be some sort of wrapper around
OPeNDAP or one of its tools (e.g. Ferret). Would you
have any suggestions or examples of similar work
that's been done?
We are currently coding in Visual Basic .NET. Is
there some way to access the Java utility you
mentioned that converts lat, long coordinates into the
array indices? Could you tell us what the WMO format
is?
Again, thanks for your reply.
Ernest
--- John Caron <caron@xxxxxxxxxxxxxxxx> wrote:
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
=== message truncated ==
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