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19990924: Tiled Grids

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  • Subject: 19990924: Tiled Grids
  • Date: Fri, 24 Sep 1999 12:26:27 -0600
>From: Brett Newkirk <address@hidden>
>Organization: .
>Keywords: 199909241636.KAA13023

>Hi Steve:
>       I have a question in regards to dealing with tiled grids. I am
>getting two tiles and need to merge them together into one GEMPAK file.
>How can this be done without overwriting a particular field from one tile
>with the same field from the second? I know that some of the NCEP data is
>being (or will be sent) around in a tiled manner as well. Thanks-
>Brett Newkirk
>
>
>Brett Newkirk    E-MAIL: address@hidden
>Office: ATG 424  Atmospheric Science/Geophysics Building
>Mailing Address: Department of Atmospheric Sciences, University of Washington
>                 Box 351640
>                 Seattle, WA 98195-1640
>Office Phone: (206) 685-2183
>

Brett,

dcgrib is capable of tiling together the grids that are available on the IDD-
eg MRF (4 quadrants), AVN thinned grids ( 8 octants) and the ECMWF.
These grids are stitched together as the pieces arrive. Each grid
is individually useable, and able to be sewn together into a composite grid.

When decoding these grids, the projection of the entire grid is used.
When the first tile arrives, it is written to the data block with the 
appropriate
offsets. When the next tile arrives, it forces the complete grid to be read
back in, the tile is written into the appropriate array locations and the
grid is written back out.

On the other hand, NCEP puts out the 10km ETA on some tiles, however, the tiles
are not complete in themselves. They are only point value offsets, and 
therefore not useful on their own withput the base grid that the offsets are 
computed 
from. Our software does not handle these, however I believe that Goeff DiMego 
at NCEP
provided a routine for stitching those offset pieces together.

Steve Chiswell