GPS trail mapping

ROBERT J MORRIS (bobmorris@rmci.net)
Fri, 17 Jan 97 10:08:44 -0500

-- [ From: ROBERT J MORRIS * EMC.Ver #2.5.02 ] --

Bonnie, Donna, KSS, Lucie and Nicco and any one else that had questions:

In using a GPS unit for mapping and obtaining the trail distance I am most
familiar with using "Trimble" equipment that is of submeter accuracy. It is
contained in a backpack with an antenna extending just above your head. A
reading of XYZ location is taken every five seconds. The data gathered on
the trail is down loaded into my computer when I get home (could be a laptop
in the field) and differential corrected. This correction eliminates any
Gov't induced error. With out differential correction you can have an error
of up to 100 meters. (I use submeter accuracy because some of my data is
used for other purposes)

The Trimble package includes all the software for data reductiion and
producing a line drawing of your route to what ever scale you are working
with. Distances, map and slope corrected, are readable. I have found that
the USGS topo maps match the GPS data very well for trails but you must
remember these maps are not really up to date. As in our case the topo maps
in this area are info from 1972!!! The trails are now different than then.

This methodology is applicable to any of the hand held units that are on the
market if they have a port for down loading info. (the majority now) As for
the software, it is available on line as freeware or shareware. Just takes
some looking for. And yes you could use a hand held plugged into a laptop
and carry it with you.

As for the Agencies having the data, You should offer to do the reduction of
the e data for them. In general the Federal agencies are using Trimble
systems. Otherwise as far as I know they mau have used the Military units
and the data is all interchangeable. NOTE the data acquired by any unit
regardless of brand is all interchangable, all you need is the proper
software. If your agency has the data and it is not in usable form a few
volunteer hours could furnish them with a lot of worthwhile information. Any
one reasonably computer wise can do the work. It is not necessary to know
programming or any thing like that. If you can access the net or E-mail you
can help your local agency reduce their data to map form. A good project for
your local equestrian organization.

Sorry but I get carried away when it comes to GPS use. Ask more questions
and another chapter will be written

Bob Morris
Morris Endurance Enterprises (GPS is one of the enterprises)
Boise, ID