RE: [pct-l] I think I already know the answer but......

["Eric Lee (Office)" <elee@MICROSOFT.com>]

I'm just now diving into the world of GPS so I've done a lot of research
recently.  The eTrek is a good choice if you want a GPS for hiking.  It's
the lightest model available right now (5.3 oz. *with* batteries) and the
battery life is supposedly about 22 hours of continuous operation, and even
longer with lithiums.  It's pretty basic in terms of features but it has
everything you need for backcountry navigation.

I'm not a thru-hiker, but I expect a GPS would be handy for parts of the
PCT.  I've heard lots of people talk about how they climbed the wrong passes
in the snow-bound Sierras and stuff like that, so I imagine it would be
handy there.  Most of the time, though, you're following a well-defined
trail and navigation isn't very challenging.

Having something like an eTrek would allow you to get rid of some other
equipment, partially offsetting its weight cost.  You wouldn't need an
altimeter to locate your position on a map, since the GPS gives you an exact
location reading at all times.  You wouldn't need a separate watch since any
GPS unit will give you the exact time direct from the satellites.  (Though
if you need an alarm to get up in the morning you'll still need a watch.)
You wouldn't need to carry *supplemental* maps for navigational purposes.

However, there are some caveats.  Most importantly, you still *need* to
carry a compass and map!

First, because any number of bad things could happen to the GPS - anything
from getting bounced down a cliff to forgetting to turn it off and draining
the batteries to a catastrophic failure of the satellite system.

Secondly, because a GPS knows position but it doesn't know orientation, at
least when you're standing still.  It can tell you that you need to move on
a bearing of 26 degrees to get to your destination, but it can't tell you if
you're actually facing toward 26 degrees or 200 degrees or whatever unless
you walk with it for awhile.  That's because the GPS only measures distances
from satellites.  Once you move with it for awhile it can figure, "I've
traveled 500 feet north and 500 east, so my operator must be moving on a
heading of 45 degrees."  This can be really inconvenient in dangerous
conditions.  A GPS and a compass together is a much more powerful
combination.

Thirdly, because a GPS can tell you where you are and where your destination
is, but it doesn't know anything about what's in between here and there.
You need a map to avoid heading into dead-end canyons or off cliffs or
whatever.  A GPS lightens the requirements for maps, but it doesn't
eliminate them.

It's also important to be aware of SA, or Selective Availability.  The U.S.
military purposefully adds errors to the satellite signals, so GPS units are
not as accurate as they could be.  For the most part, they're accurate to
within +/- 300 feet including SA, which is fine for backcountry navigation.
However, the altitude part of the readings are most affected by SA and may
vary by up +/- 1000 feet, so don't count on using your GPS as an altimeter.
The GPS makes an altimeter unnecessary for navigation, but if you just like
to know how high you are, a GPS unit isn't going to do the trick.

Eric

-----Original Message-----
From: Paul Nickodem [mailto:Dharmabum64@worldnet.att.net]
Sent: Sunday, February 13, 2000 6:31 PM