[Xastir-dev] Position accuracy

[Gerry Creager N5JXS]

At this point, the differences between NAD83 and WGS84 are fairly 
trivial, amounting to a centroid difference of 2m, which usually 
translates to mm at the surface.  So... it's not a big delta and not 
generally worth the effort.  We're not doing surface geodesy at this 
point, and in my opinion, if we started doing serious geodesy with 
xastir we WOULD have to revisit a lot of the code.

73, all.  Off to Boulder (and Ft Worth, then back to Boulder) for the 
week...

gerry

Curt Mills, WE7U wrote:
> On Sun, 7 Dec 2003, Gerry Creager N5JXS wrote:
> 
> 
>>I've seen Jack's response, but I've got to comment further.  The more 
>>conversions we do, without telling the world what datum we're using the 
>>more times someone's gonna misrepresent what the data mean.  We need to 
>>see a new version of the compressed format that tells you what datum is 
>>in use.  Perhaps this is something for Scott's OpenTrac project rather 
>>than APRS...
> 
> 
> APRS dictates WGS84, although many GPS's out there are set to NAD27
> so that they more closely match the street maps people are using.
> It's a real mess.  It'd be nice if the protocol allowed specifying
> the transmitted datum, or at least have the clients convert to WGS84
> for transmission.  Of course, that's on our RFE list, but we could do
> it with the libraries at hand.
> 
> Also, in the code we often equate NAD83 and WGS84 as being equal, and
> don't pay much attention to rounding errors and the like as it
> doesn't make much difference for APRS use.  If we were to start using
> Xastir for purposes needing higher precision, much of the code would
> have to be revisited.
> 
> Most of the things mentioned by Jack don't require higher precision
> than already supplied via Xastir though.
> 

-- 
Gerry Creager -- gerry.creager at tamu.edu
Network Engineering -- AATLT, Texas A&M University	
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