Though the web page comments that GPS location is not supported(Obvious reason)..
POSITION REPORTING: Of course GPS does not work underground, but any two people looking at the same map can report their position by simple grid marks on the map. The resolution and accuracy is as good as the map was drawn and the precision of the person estimating his coordinates on the map. As long as the cavers have a paper copy of a gridded map which is the same as everyone else including observers topside, then everyone will see where everyone else is on that map. The caver just manually enters his lat/long by looking at the grid on his paper map! For example, this version of the map has the grid overlayed. Team1 is located at N34 45.93 and W87 45.35. It does not matter if this is geologically accurate or not. What only matters is that everyone is using the same copy of the same map
..it failed to mention that Vicinity Tracking can be set up by each digipeater within the system and will show(display the closest heard digi in it's digi path) the mobile station. Similar to cellphone technology.
WIDEn-n IMPLEMENTATIONS: With the New-N paradigm, since about 2004,
just about all packets now contain a traceable path. This means that
we can identify what digi was the first to hear the packet, and
therefore approximately where on Earth the originating station is
INTERIOR TRACKING IDEA
can also work indoors such as in convention centers and other large
distributed structures by simply reducing the range of indoor digis.
Simply install nearly-deaf digipeaters called BOXn digipeaters in each
major room area. A good example is the HARA Arena at the Dayton
Hamvention which consists of approximately seven large interior spaces.
The APRS software simply plots the location of interior users in the
vicinity of each of about a dozen-or-so BOXn digipeaters that last heard
the users packet. THis process is called VICINITY Tracking and can
also be used to approximate the location of new stations near any
digipeater until a valid posit is received.
The Interior application of Vicinity Tracking can actually be more
accurate than GPS (under 50 meters), and can be adjusted to the size of
the rooms in any given application. A receive range of about 50 m (150')
is the nominal design range. As long as all users set their transmitters
to approximately 100 mw, then the threshold of these ranges is more
accurate than one might think. THis is because with the BOXn digi's
antenna in the clear in the room, then the path to any walking user is
almost line-of-sight and follows the 1/r squared law quite well. Since
it is a square law, the detection difference between 50 and 100 meters,
for example is over 6 dB.
These BOXn digipeaters may even be used outdoors so that users in a
confined area, such as the flea market at Dayton, can be localized without
them having to carry a GPS. Since each BOXn digi is able to have its own
hearing range and it conveys that to the system in its BText, these BOXn
digis may use a longer range.
Even though the reliability of this system is based on an assumed 100 mw
transmitter power from the users, the threshold range for a 1 watt user
in a 50 meter system would be only 3 times greater or about 150 meters.
If most BOXn digis are confined to physical rooms, the loss through
adjacent walls will probably reduce, if not eliminate this problem.
BOXn DIGIS: These are standard APRS digipeaters that use either the
PacComm or KPC-3 TNC's. These TNC's are given the MYCALL of BOXn and
the UIDIGI of RELAY and a local application name such as HARA (at Dayton).
The local interior path name (HARA) is the preferred via PATH for users
indoors to prevent bedlam on the 144.39 frequency from the hundred
vehicles in the parking lot who may also digipeat RELAY packets. But
RELAY is included for those few people who forget. Any packet heard
in the vicinity of any of these BOX'es will be digipeated with MYCALL
substituted so that all APRS software can tell which digi is closest
to the user. At Dayton, the old frequency of 145.785 may be used for
interior tracking to help split the load on 144.39 and to allow just
RELAY to be used.