Re: [Opengrads-devel] geolocated sat data...

[Arlindo da S. <da...@al...>]

On Jan 23, 2008 8:48 AM, Mike Fiorino <mfi...@gm...> wrote:

> hi arlindo, see
>
> ftp://ftp.nhc.noaa.gov/users/fiorino/HURSAT-BASIN.NA.2006.06.27.21.beta.nc
>
> this comes from a big tropical cyclone satellite data set.  sdfopen
> works fine and i complained to the developer that the file did not have
> a time dimension (for templating ala xdfopen).  is this form useful for
> satellite data?
>

Actually, these are very nice files.  It uses 16 bits to hold the brightness
temperature, although is most instances 8-bits would be plenty.  Except for
efficiency issues, one should be able to read it into GrADS, with the proper
PDEF. Another nicety is that it uses Mercator rather than the
"Geostationary" projection and the bounding box is a stored as an attribute
in the file.

At this point "gxout grfill" is the best option to render this in GrADS. In
the original opengrads sources, I had introduced the option for "gxout
pixmap" which draws a single pixel at the center of the box rather than
doing a rectangle fill. We should be able to easily implement this as a udc.
Better yet, we need a "gxout image" much like in matplotlib, but this would
require changing the metafile format, something better left for v2; besides
Brian has plans for handling images in v2. The "pixmap" extension is a
reasonable compromise for v1.9.

However,  for ingesting it in Python I'd use the 100% Python NetCDF/OPeNDAP
reader that comes with basemap. I am thinking about subclassing
PIL.Imageand creating the GaIL class for handling satellite images in
pygrads.
Supported formats would be AREA,  this brand of netcdf files, Geotiff and
Tiff/JPEG/GIF (provided one prepares a ctl like file with the
geo-referencing when this is not there.)

In any event, it would be very helpful if we could get the software that
wrote these nc files. I haven't had much luck getting software out of NCDC.
I have made multiple requests for their Fortran AREA header without much
luck. Being at the NHC (and being Mike Fiorino) you may have better luck
than I.

At this point I am consumed with finalizing the Win32 build. I almost there.
Then I'll return to PyGrADS and finish up the satellite image handling.

          Arlindo

-- 
Arlindo da Silva
da...@al...