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[aprssig] future problems with NWS radar images?

Steve Dimse steve at dimse.com
Tue Mar 29 05:02:41 UTC 2005


On Mar 28, 2005, at 5:59 PM, AE5PL Lists wrote:

> Yes,
> this does make some difference in plotting, especially in the outer 
> half
> of the coverage area.
>
I did a very quick overlay of the two maps

http://www.aprs.net/overlay.jpg

I think with a little care in the scale and rotation of the two images, 
one could come up with a better fit, but even this is only a few pixels 
error over most of the map. The big concern here is the tilt of the 
map...the current images must be rotated quite a bit to align with the 
new one. As presently implemented, geo files cannot handle this 
rotation, it would take a third point to define the rotation. There is 
no reason this cannot be implemented should the NWS switch to this new 
style, but it would mean not only all programs using 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?

Steve K4HG





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