[pct-l] RE: GPS Altimeters

[msaenz at mve-architects.com (Mike Saenz)]

GPS on the PCT: Unnecessary.

I carry one, but more for the average speed/mileage/altitude info than
for locations.
I've been considering leaving it home the past few hikes because I now
know that I hike an average 2 MPH with a fully loaded pack on a mountain
trail, 3 MPH with just a day pack. I can monitor progress by glancing at
my wristwatch now. To me, altitude corresponds to how bad I'm sucking
wind... I now know that if I'm really winded, I'm above 10k.

Advantages of barometric altimeter: Weather prediction (see my previous
post on "scariest sounds").

Interesting factoid: GPS  is capable of accuracy within an inch or two
(maybe less, this is "Classified" information). The US government
requires that commercially available GPS units are disabled to provide
no greater than 3 meter accuracy.

I tend to locate myself on a map by knowing what trail I'm on and
finding the corresponding elevation topo line that crosses that trail. I
don't think I've used the long/lat coordinates more than a handful of
times since I got my GPS.

If you must get a GPS, I suggest the smallest, lightest unit: The Garmin
Geko. Has all the functions and capabilities you'd want in a GPS unit,
and is very small and light.
Mine's got just about ALL the functions a GPS could offer and is a
brick: The Garmin Rino.

I once got all 12 satellite bars locked on (WAAS enabled) in Joshua Tree
Nat'l Monument! The accuracy report from the unit was down to 3 feet.


Michael Saenz, Associate Partner
McLarand    Vasquez    Emsiek   &   Partners,   Inc.
A r c h i t e c t u r e  |  P l a n n i n g  |  I n t e r i o r s
MVE       MVE    Institutional       MVP    International
w  w  w   .   m  v  e   -   a  r  c  h  i  t  e  c  t  s   .   c  o m

-----Original Message-----
From: pct-l-bounces@mailman.backcountry.net
[mailto:pct-l-bounces@mailman.backcountry.net] On Behalf Of eric lee
Sent: Sunday, September 18, 2005 8:13 AM
To: vichanson@juno.com; pct-l@mailman.backcountry.net
Subject: [BULK] - RE: [pct-l] GPS Altimeters

Well I guess I'll chime in on this one since I sell GPS units and
altimeters as a side job, in addition to teaching basic hands on GPS
classes. While a GPS may not be a necessity for a normal PCT hike they
do have many useful aplications for back country use especially in the
dark, fog, and snow storms. While all GPS units are capable of giving
the user an altitude reading, units such as the legend depend completely
upon the units ability to pick up satellites. The more satellites it can
pick up the better it can triangulate your altitude. I've found that
while mountaineering in the high sierras this is usually not off by more
than 50-80ft, when I have 4+ satellites. Problem is, if you get poor
reception(in trees/canyons) or can only pick up a few satellites, this
will greatly affect your accuracy, possibly even eliminating any
altitude reading.
The barometric altimeters on the other hand are always functioning.
Since they are based off barometric pressure changes as you move up and
down elevation they can fluctuate due to weather changes or just rapid
gain in altitude. I've used a Suunto barometric altimeter for a few
years and it does require periodic calibration throughout the day as I
climb(usually gaining 1500-2000ft/h). The other nice thing a barometric
altimeter does is to track altitude gain and loss totals, in addition to
ascent and descent rates. While this may not be a necessity, its very
interesting. So is one better than another, no. They both have their
advantages and disadvantages.
In particular the Garmin Summit also has a moving compass. Basically
this functions as a standing magnetic compass built into the unit. The
Legend only has a moving baring, so if you are standing still the
pointer will not readjust, you need to take several steps in any given
direction before it adjusts. I hope that helps and that I didn't miss
anything or mistate anything.
Eric J Lee


>From: Vic Hanson <vichansonperu@yahoo.com>
>Reply-To: vichanson@juno.com
>To: pct-l@mailman.backcountry.net
>Subject: [pct-l] GPS Altimeters
>Date: Sat, 17 Sep 2005 19:54:40 -0700 (PDT)
>
>I am still confused on GPS units, please help! The more expensive ones 
>have a barometric altimeter. Acording to the Garmin website, it takes 
>two sats to get a location, three to get altitude. I take this to mean 
>that any GPS can give you the altitude reading, it this correct? If so,

>what is the advantage of having a barometric altimeter in a GPS? I was 
>with a friend a few weeks ago, he was using a Garmin Summit. When he 
>checked the altitude, it asked if he wanted to calibrate by satelite. 
>When he did, it showed an altitude over 500 feet greater (we were at 
>16,000', in a car, having lunch!).
>
>I am trying to decide between the Legend and the Summit. If I can get 
>altitude with the Legend (no bar. alti.), I can't see spending the 
>extra for the Summit. I already have a alitimeter watch that needs to 
>be constantly recalibrated.
>
>Thanks,
>
>Vic
>
>
>
>
>Which is more accurate -- the barometer-type altitude or a good 
>calibrated GPS?
>And have you compared your altimeter readings with topos to see what 
>sort of relationship and reconcilement there is?
>
>
>
>
>A GPS relies upon triangulation from NavSat signals so it does not have

>to be recalibrated by the user. The accuracy of a GPS depends upon the 
>instrument, of course, but more importantly upon the signal quality. 
>When my GPS receives a poor signal it continues to show a solution, but

>the probable accuracy is also displayed. Under good conditions its 
>accuracy may be 7-8 ft. but among the trees or in a canyon the accuracy

>can degrade to 200-300 feet. That applies to the X-Y map position 
>accuracy as well as the "Z" (altitude) accuracy. A GPS has the useful 
>ability to periodically record its X-Y-Z locations, but when moving in 
>and out of areas with poor signal strength it could show that I have 
>changed altitude several hundred feet when in fact the altitude was 
>approximately constant. As they say about fat pills and gas mileage, 
>"your results may vary", but I have not found that altitudes from a 
>hand-held GPS are as consistent, accurate, and reliable as those from a

>good barometer, provided the barometer is properly calibrated. However,

>stopping to record a barometer reading every few minutes would be a
real pain.
>
>
>
>Steel-Eye
>
>
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