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20051102: GRIB2 -> McIDAS



>From:  "Valentijn Venus" <address@hidden>
>Organization:  ITC
>Keywords:  200511021126.jA2BQM7s005334 McIDAS GRIB2

Hi Valentijn,

>I hope you are both well. I was wondering if any of you have worked on
>a ADDE server for serving MSG products in GRIB2 format (such as CLA and
>CLM) as received through the EUMETCAST service?

I have not.

>At the MUG annual
>meetings they discuss the support for GRIB2? Tom, any news on that?

Yes, support for GRIB2 format model output was one of the items
discussed.  I think I remember correctly that they are making good
progress and that support for GRIB2 is expected in their v2006 release
next May (the Unidata release lags the SSEC release typically by 1.5
months).  They have also made good progress in serving GRIB
data directly through ADDE (with our without using a MYSQL frontend).

>Even if a GRIB2 server would be added to McIDAS, the navigation is
>still a bit foreign. Its the projection used by Eumetsat
>(www.eumetsat.int) for its Meteosat-8 imagery. If it is the same as is
>defined in the current HRIT MSG server code (msgtaget2.f) than it
>wouldn't be to complicated. The 90 Space View Perspective or
>Orthographic projection is defined in documents EUM/MSG/ICD/105 and
>EUM/MSG/SPE/022 (available at their website under
>Publications/Technical Documentation). Here is a section from it:
>
>--------------------------------------------------------------------
>                        Header : GRIB
>                    Discipline : 3 Space products
>                  GRIB Edition : 2
>                   GRIB length : 3444913
>            Originating Center : 254 EUMETSAT Operation Centre
>        Originating Sub-Center : 0
>Significance of Reference Time : 3 Observation time
>                Reference Time : 2005:4:18T12:0:0
>                Product Status : 1 Operational test products
>                  Product Type : 6 Processed satellite observations
>         Number of data points : 13778944
>                     Grid Name : 90 Space View Perspective or Orthographic
>                     Grid Shape: 3 Earth oblate spheroid with axes
>specified by produ
>cer
>        Oblate earth major axis: 6378.14
>        Oblate earth minor axis: 6356.7554
>Number of points along parallel: 3712
>Number of points along meridian: 3712
>Latitude of sub-satellite point: 0.0
>  Longitude of sub-satellite pt: 0.0
>  Resolution & Component flags : 0
>         i direction increment : 3566.0
>         j direction increment : 3561.0
> X-coordinate of sub-satellite : 1856.0001
> Y-coordinate of sub-satellite : 1856.0001
>                 Scanning mode : 192
>                   Basic angle : 0
>        Altitude of the camera : 7.4533146E8
>        X-coordinate of origin : 0.0
>        Y-coordinate of origin : 0.0
>            Product Definition : 30 Satellite product
>            Parameter Category : 0 Image_format_products
>                Parameter Name : 7 Cloud_mask
>               Parameter Units :
>       Generating Process Type : 8
>                  ForecastTime : 0
>            First Surface Type : 0 Reserved

It would be useful to have some example GRIB2 products so that I could
forward them to SSEC for review.

>Tom, I would like to get some handson with importing the data. I was
>thinking of converting it to a binary first, and then running MAKAREA &
>MAKNAV.

This is a good thought, but MAKNAV does not appear to support this
projection.  I have been discussing some mods to MAKNAV with another of
my users who wants to (re)create GVAR images in AREA format.  My
inclination is to add support to MAKNAV to extract the navigation block
out an existing image and write it into the target.  This approach has
worked well in the past for a user dealing with SeaSpace TeraScan (tm)
imagery.

>At http://www.nws.noaa.gov/mdl/NDFD_GRIB2Decoder/ there is a
>converter from GRIB2 to binary float files (.flt) which can be also
>used with GrADS or ESRI Spatial Analyst. Any suggestions?

MAKEAREA requires that the data to be imported be integer, not floating
point:

  Remarks:
  MAKEAREA converts a flat file of brightnesses (1, 2, or 4-byte data)
  into a 1-byte AREA scaling the data appropriately

If you can write out flat, binary files with integral values, then
MAKEAREA can write it to a new AREA file.  If you have any image that
contains the proper navigation block for the navigation in the GRIB2
messages, then my proposed mod to MAKNAV should work.

The timetable for my MAKNAV work is relatively short:  the other user
needs to be able to move the data created by IDL back into AREA files
so they can be used in McIDAS.

Cheers,

Tom
--
+-----------------------------------------------------------------------------+
* Tom Yoksas                                             UCAR Unidata Program *
* (303) 497-8642 (last resort)                                  P.O. Box 3000 *
* address@hidden                                   Boulder, CO 80307 *
* Unidata WWW Service                             http://www.unidata.ucar.edu/*
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