[aprssig] Re: Ambiquity

[Robert Bruninga]

Although the D7(g) model and D700 both also support
position ambiguity, the early D7A did not.

So APRSdos has another 1 mile ambiguity feature for the
airline traveler (without GPS) so that as he travels from
city-to-city he can enter approximate manual LAT/LONGs
and at least show up on local maps without implying
an exactly WRONG precise position.  

If a LAT/LONG ends in precisely .00/... .00, then my code
makes the asumption that this is a manual entry of
ambiguity in a device that otherwise does not allow
ambiguity to be entered.  This "assumption" is right
99.99% of the time, beacuse there is only one chance
in about 10,000 that a position actually falls within 60
feet of such a position.

This was also proposed to all other authors, but I dont t
think any of them implemented it.  To see if your software
supports position ambiguity, zoom into my house
WB4APR and if it shows as a precise ICON on any map
with streets on it or below a 4 mile range scale, and
if it gives you no indication that you are looking at an
ambiguous position, and the scale of that ambiguty, then 
your software is presenting a fake position and is not 
presenting you with the proper APRS display of the real 
information intended by the sender.

Or look at it this way  If your software shows my icon
at a position ending in .00/... .00 then it is creating false
positions and displaying erroneous data.  Dont trust it! hi hi

Preserving position ambiguity and displaying it to the end
user is fundamental to APRS and is required to maintian
the integrity of the system.

de WB4APR, Bob