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Re: [gembud] nex2gini navigation errors in GEMPAK

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  • Subject: Re: [gembud] nex2gini navigation errors in GEMPAK
  • Date: Fri, 28 Sep 2007 10:35:03 -0600
John,

When creating a GINI format product, the projection and data area have
to be compatible with the GINI projection model- eg, when using an LCC
projection,
you have to specify a tangent cone and not a secant cone (eg angle1 ==
angle3)
since GINI itself only supports that special case.

Also, the lat/lon boundaries have to be representable to the precision
of numbers
that can be expressed in the GINI header. If you attempt to create a
boundary where the computed DX and DY of the pixel are not compatible,
your image projection will 
be shifted. The example in the help for nex2gini provides an example of
a valid region:
        GRDAREA  = 23;-120;47.2634;-63.5664
         PROJ     = lcc/40;-100;40
         KXKY     = 4736;3000


Steve Chiswell
Unidata User Support


On Fri, 2007-09-28 at 09:34 -0600, john wrote:
> I am running Gempak 5.10.3 on Fedora Core 6 at home.  I installed from 
> source, and everything works fine.  I have a NOAAPORT feed providing data, 
> and that too is working fine.  All single site radar data is visible in NMAP 
> and looks great.
>  
> I am attempting to use nex2gini to created mosaic radar images.  I am using 
> the example settings from chiz for creating a 1km mosaic.  The program runs 
> without error, and creates a file of proper size (compared to examples of 
> good ones from other sources).
>  
> My problem is, the navigation is messed up on all the images.  Data is 
> displaced by 50-100 miles.  Looping the images in NMAP show that the errors 
> are consistent.  I have made numerous attempts using different projections, 
> gareas, station tables, kxky values, etc.  All images come back with 
> displaced nav when displayed in NMAP or gpmap.  Running nex2img results in 
> the same thing.
>  
> This morning I cleaned and remade GEMPAK.  No errors.  No change in output.
>  
> Anyone have any ideas?  I'm stuck.
>  
> John Hart
>  
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-- 
Steve Chiswell <address@hidden>
Unidata