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[aprssig] PHG and HAAT

Brian Webster bwebster at wirelessmapping.com
Thu Oct 13 22:51:36 UTC 2005

    While I agree on your statements most of the time I must disagree with
you here as far as establishing a HAAT value. Long ago I thought I would be
able to guess mine like you mentioned. I sit on a 1420 foot high mountain
and look down on a lot of area, I also have many other hills that are higher
around me. In using software to determine my HAAT (Radio Mobile and a web
site that has since disappeared) my location comes up with a negative value.
This is not a simple calculation for others to guess unless they live in
relatively flat areas. In complex terrains, this guessing game will make the
PHG circles useless. In my case there is no provision to show directionality
in multiple directions. I do RF engineering and coverage mapping for a
living and can tell you in hilly terrain the PHG circles are mostly useless.
    The simple answer to this, especially in the case of UI-View is for
folks to examine the effective path of each station they can see on their
map, since they can SEE a digi on a map (this is APRS) and if they see a lot
of surrounding stations that have this call sign as the first hop in their
effective path they can assume the coverage of a digi much better than a PHG
circle. If an operator were to take things further and install UI-path or
use Radio Mobile as an APRS client they can actually see the path hopping
from site to site and get the idea of the coverage as well. It would also be
a good thing as some have suggested, for someone to create a plug-in or
feature that would use all of the APRS stations with a particular station
call sign as the first hop in the path and create an irregular polygon to
show the footprint of the particular station/digi. While it won't be
completely accurate it would be much more like reality than a PHG circle.
This might even be able to be done at a server level such as Findu. I think
it could be displayed as an Area Object but not being real knowledgeable on
the APRS spec I don't know. This type of system would further remove
guessing about coverage areas. I do agree knowing the area a particular
transmitter covers is important in a tactical mapping system. Having to many
people create this without strict standards applied gives inconsistent
results thus making it's value much less.

Thank You,
Brian N2KGC

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