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[aprssig] future problems with NWS radar images?

AE5PL Lists HamLists at ametx.com
Tue Mar 29 11:55:23 UTC 2005


> -----Original Message-----
> From: Steve Dimse
> Posted At: Monday, March 28, 2005 11:03 PM
> Subject: Re: [aprssig] future problems with NWS radar images?
> 
> geo files would need to be updated. If I read Pete's 
> explanation correctly, it sounds like the present radar 
> images are the ones which are not the orthogonal projection 
> geo files expect, so perhaps new geo files with the new image 
> projection, even without rotation, would be more accurate.  
> Do I have that right Pete?

That is correct.  The current single radar site gifs are not orthogonal,
they are stereographic centered on the radar site.  I have tables at
http://www.aprs-is.net/wx/wxradarsites.htm which gives the corners for
each site.

You are also correct that there is only a few pixel difference since the
scale is only a 120 mile radius.  However, that is can represent up to a
mile difference in the outer areas of the map.  I use the stereographic
project in jFindu mapping for NWS radar images.  The formulae that I use
are derived from
http://mathworld.wolfram.com/StereographicProjection.html  As you
probably are already aware, there are some c libraries out there that
also do the different projections.

73,

Pete Loveall AE5PL
mailto:pete at ae5pl.net 




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