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[GEMPAK #NZA-884392]: GEMPAK - grid box versus grid point coordinates

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  • Subject: [GEMPAK #NZA-884392]: GEMPAK - grid box versus grid point coordinates
  • Date: Tue, 12 Sep 2006 15:21:24 -0600
David,

The projection information defines the individual grid point locations, not a 
box location.
The data value is the value at the grid point.

If you want the lower left point to be exactly at -2;-2 and the upper right
point to be at 2;2 and a CED projection with .1 degree spacing in the X and Y, 
use:

 GRID NAVIGATION: 
     PROJECTION:          CED                 
     GRID SIZE:           41  41
     LL CORNER:              -2.00     -2.00
     UR CORNER:               2.00      2.00

Eg, KXKY=41;41. There is one more row and column of data than what you call a 
box.

Note that the ability to use the "#" character in KXKY is only for CED grids, 
and not
for any other projection, and the number of points is by convention.

Steve Chiswell
Unidata User Support


> Institution: NCAR
> Package Version: 5.9.3
> Operating System: linux 2.6.17-1.2157_FC5smp
> Hardware Information: i686
> Inquiry: Does the longitude (or latitude) of a GEMPAK grid point correspond 
> to the edge or to the center of the corresponding grid box?
> 
> For example, when I create a GEMPAK grid with GRDAREA=-2;-2;2;2 and 
> KXKY=#0.1;0.1, I see the range of longitudes is -2 to 1.9 degrees when I 
> print the LONR field with gdlist.
> 
> That suggests that the grid point longitude is actually the western edge of 
> the grid box, since this would perfectly span the requested range of -2 to 2 
> deg.
> 
> However, if I assume the grid point longitude is the center of the grid box 
> (as usually done in meteorology), the grid spans -2.05 to 1.95 deg.  Which is 
> correct?
> 
> 
> 
> 


Ticket Details
===================
Ticket ID: NZA-884392
Department: Support GEMPAK
Priority: Normal
Status: Closed