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20040622: McIDAS - Regarding GRIB lat lon injest



>From: Micah Epps <address@hidden>
>Organization: DRS Weather Systems, Inc.
>Keywords: 200406222126.i5MLQBWb014805 McIDAS GRIB latitude longitude

Micah,

Sorry it has taken so long to get back to you on this.

>When McIDAS injests a gridded binary (GRIB) file, how should the latitude
>and longitude(s) be encoded?

The McIDAS-XCD GRIB decoder can handle GRIB messages that are formatted
according to the descriptions in:

                     Office Note 388
                         GRIB

                     The WMO Format
                          for
          The Storage of Weather Product Messages
                  in Gridded Binary Form
                       as used by 
                  NCEP Central Operations


                  GRIB Edition 2 (FM92)


>Are the units degrees, Degrees-minutes-seconds or Radians?

The format of latitude and longitude is typically millidegrees (degrees x 1000).

>Is the origin Prime Meridian @ equator?

If you mean origin of lat,lon measurement, then yes.

>Which hemispheres are denoted by a positive lat or lon?  

By international convention, the western hemisphere has negative longitudes
in GRIB messages.  McIDAS-XCD converts these to positive longitudes to
match its convention.

>Thank you.

No worries.

>-Micah
>-- 
>Micah T. Epps
>Software Engineer
>(334) 347-3478, ext. 228
>DRS Weather Systems, Inc.
>128 South Industrial Blvd.
>Enterprise, AL 36330

Cheers,

Tom Yoksas
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