Re: GPS to calculate mileage

["Duncan Fletcher" <dfletche@gte.net>]

An alternative is to use the USGS topo maps and program called Ozi-Explorer
($50 shareware for full version, see
http://www.powerup.com.au/~lornew/oziexp.html) which can transfer
information from map to gps and back. The government has recently raised the
price of these, but they are public domain and can be copied freely - there
are some cheaper alternative sources (do a search in deja news in the
sci.geo.satellite-nav). For some states, they are available for free
download over the internet (see http://mcmcweb.er.usgs.gov/drg/avail.html).
These will show contour lines, but there is no inbedded contour database as
in Topo!. OTH, that data base was frequently off by several hundred feet in
their Colorado demo map.

But regardless of the topos used, be aware they are all based on the USGS
source maps which in many cases are fairly old. Trails are frequently
rerouted - frequently with the addition of switchbacks in mountainous
terrain where the original trail ran straight up the hill. And in areas of
switchbacks, map scales do no allow an accurate reflection every short
switchback. Roads should generally create fewer problems.

Duncan Fletcher
dfletche@gte.net


-----Original Message-----
From: Lynn Kinsky <lkinsky@silcom.com>

>

>
>Much easier and better than method 2 is to use a computer and the
>software/topo maps from Topo! (http://www.topo.com).  On the trails we used
>for our recent Sage Hill NATRC ride, where we could get to most of them to
>check with vehicle odometers, the comparison between the odometer and the
>topo software was well under 10% (in fact, given that the odometer only
>reads in 0.1 miles, the comparison appeared to be dead-on).  The GPS can be
>very handy for recording waypoints and then letting you find them on the
>topomap on the computer for places where your trail is doing a lot of cross
>country.  The topo software prints out trail elevation profiles as well --
>plus it generates your ride maps.  Most of California -- in fact large
>portions of the US recreational areas -- are now available on the CDs.
>
>
>-- Lynn K. (Santa Ynez, CA)
>   http://www.silcom.com/~lkinsky
>
>
>