Variable Grid possible?

[Reto Stauffer]

Dear Usergroup

A few weeks ago you sent me a wonderful hint about the topic "Variable Grid
possible?" (you can see the answers below).
I did some web-research but i could not find any good help topics.

What i understood (about the PDEF function):
- I have a data matrix (data-value, longitude, latitude) (for ex. 10x5)
- I have a GrADS-internal regular Grid, for example XDEF 5 LINEAR 0 10, YDEF 3
LINEAR 0 10 (-> 5x3)
- I compute a interpolation matrix wich describes wich value (from my original
10x5 matrix) should be plotted in my regular grid (5x3). So my i and j matrix
need to have the same dimension like my regular grid (5x3). There is also a
third matrix (only one-point-interpolation) wich contains my wind rotation
values (5x3).

In the documentation is written that i have to store the three matrices
(i,j,windrotation) into a binary file. But witch binary file type and wich
structure? I was also afraid  because i could not find any example-datasets in
the internet.

Does any of you have a better description for the PDEF function or a
sample-dataset wich show the features of this PDEF function?

It would be great if someone could help me.

Greetings
Reto Stauffer, Austria



--------------------------------------------------
--------------------------------------------------
--------------------------------------------------



Am 10.09.2009 um 20:00 schrieb Jennifer Adams:

That kind of data grid (with 2-dimensional coordinate variables) doesn't fit the
current gridded data model in GrADS. We have talked about implementing a new
data model, quasi-regular data, that would fall somewhere in between regular
grids and station data. But that is not likely to be implemented any time soon.
For now, interpolating to a regular grid with PDEF is the only way to handle
that kind of data directly using GrADS.
--Jennifer

On Sep 10, 2009, at 11:37 AM, Christopher Lynnes wrote:

Jennifer,
  The PDEF GENERAL capability looks quite useful, but made me wonder
if GrADS does or will support variable grids in netCDF, where the data
are defined according to the CF-1 convention for two-dimensional
latitude and longitude coordinate variables
(http://cf-pcmdi.llnl.gov/documents/cf-conventions/1.4/cf-conventions.html#id2984605
).
  We have a service to convert our AIRS swath data to netCDF files
with this convention, which allows tools such as IDV and McIDAS-V to
read and project them.  However, attempting an sdfopen in grads
2.0.a7.1 leads to the "no discernable X coordinate" error.
  An example file can be obtained via the URL:
http://aurapar2u.ecs.nasa.gov/airspar1/daac-bin/OTF/HTTP_services.cgi?FILENAME=%2Fdata%2Fs4pa%2FAqua_AIRS_Level2%2FAIRX2RET.005%2F2006%2F161%2FAIRS.2006.06.10.202.L2.RetStd.v5.0.14.0.G07345043455.hdf&LABEL=AIRS.2006.06.10.202.L2.RetStd.v5.0.14.0.G07345043455.nc&SHORTNAME=AIRX2RET&SERVICE=NetCDF&VERSION=1.02

On Sep 10, 2009, at 7:58 AM, Jennifer Adams wrote:

You can use the PDEF GENERAL (aka PDEF FILE) option to tell GrADS
how to map each grid point in your 1-D vector into a 2-D lat/lon
grid. Please see http://www.iges.org/grads/gadoc/pdef.html
The example at the bottom of the page does something very similar to
what you'd like to do.
--Jennifer

On Sep 9, 2009, at 7:03 AM, Reto Stauffer wrote:

Hy there

I try to plot some Satellite-Data with Grads. It was "no problem"
to produce a
netCDF file wich i can import into GrADS and display the test-
dataset.

But now i have a question up to you. Normaly GrADS plots only onto
a linear
Grid. My netCDF-File only contains a one-line-vector with longitude
and
latitude boundries.

Is there any possibility to import long/lat as a 2-D matrix wich
discribes my
own grid? I cannot found any good information about that.

Test-Dataset, int [0;10] with own colormap:
http://dudecom.ch/satpress/wp-content/uploads/2009/09/20090909_grads_colormapexample-543x400.png

If anyone has an idea it wold be great to send me a request.

Best regards
Reto, Austria

--
Jennifer M. Adams
IGES/COLA
4041 Powder Mill Road, Suite 302
Calverton, MD 20705
jma at cola.iges.org




--
Christopher Lynnes             NASA/GSFC, Code 610.2
301-614-5185

--
Jennifer M. Adams
IGES/COLA
4041 Powder Mill Road, Suite 302
Calverton, MD 20705
jma at cola.iges.org