Which model should
I buy?
I can’t give a simple answer that’s right for everyone.
If you’re a technophile, you may want to spend the money to own
a receiver that is bundled with additional gizmos such as electronic
compass, electronic altimeter, downloadable maps, or FRS radio. If you
do, be sure to invest the time to understand what it does with all these
things. Some models either couple the barometric altimeter with the
GPS-determined altitude to display a hybrid or use the GPS altitude
to reset the barometric altitude. If you understand everything yours
is doing, you may be able to turn these features off. Similarly, some
models may combine your heading (the direction you’ve been moving)
with your bearing (the direction the device is facing) in a way that
may be misleading.
The maps incorporated into the map models may be pretty good; they’re
not USGS maps, however. Be sure that you understand that you usually
have to buy the maps on a CD as a separate item.
If you use the extra gizmos, the batteries won’t last as long
as they would in the unadorned receiver in the same model series.
Above all, never get so enamored of the extra features that you neglect
to carry an old-fashioned paper map, an old-fashioned magnetic compass,
and perhaps an altimeter, preferably an old-fashioned aneroid type.
Otherwise, if you lose or break your receiver or run it out of batteries,
you may be very literally lost.
If you’re a bit of a technophobe, or even if you’re comfortable
with technological marvels but recognize that the simpler a gadget is,
the more likely it is that you will understand correctly what it’s
telling you, you may prefer the stripped down models, which will, after
all, be cheaper. I have not found that the costlier, bigger receivers
work any better than the tiny inexpensive ones. For the most part they
perform the same functions.
A few models do not accept a cable to connect to a computer for transferring
waypoint data. The ability to manage waypoints on a computer, preferably
within a map-generating program, is to me so valuable that I would not
buy a receiver that lacked a cable interface. Some models are bundled
with the necessary PC interface cable; for others you have to purchase
the cable separately. GPS manufacturers’ cables are usually pricy;
send me an e-mail if you want to risk buying one on the cheap from an
independent vendor.
There are definitely GPS lemons. Whether they are design flaws afflicting
an entire model, or manufacturing errors restricted to individual units,
I don’t know. I recommend performing a simple test, preferably
before buying your receiver, but if that’s not possible, then
immediately afterward. Here it is:
Borrow a good receiver from a friend, and take it and the one you’re
about to buy out into an open space to the north of a relatively tall
building. Turn them on and wait until they have both fixed your location.
Walk up to the base of the building wall, so that only the northern
half of the sky is visible. At this point, both receivers can be expected
to fail. (Under unusual circumstances they may not.) Some models will
hang on to the last calculated position for some time, perhaps a few
minutes, before admitting that they haven’t a clue where you are,
so be patient.
After both receivers have lost your position, walk slowly northward
with one in each hand. Watch them both closely, and note when they recover
position. If the one you’re contemplating buying is noticeably
more sluggish in locating you than the other, don’t buy it!
Although this is a good test for the city, a better one is to practice
outdoors with your new toy together with a borrowed unit that you know
is good. Practice in the woods, in valleys, on north-facing slopes.
If your new receiver doesn’t behave as well as the one you’ve
borrowed, return it.
I recommend strongly that you buy your receiver from a reliable shop
rather than over the Web. In Seattle I have found REI and West Marine
to have good return policies, although doubtless other retailers are
also good.
WAAS? For now and the foreseeable future, forget it. It depends on auxiliary
satellites that are low in the southern sky, so that at best they are
likely to be visible only when you’re on a summit, which is where
(a) you probably know where you are anyway, and (b) your receiver will
work flawlessly without WAAS. It’s true that WAAS might reduce
your position error from fifteen or twenty meters to three or four,
but you probably can’t read your map more accurately than to within
about twenty meters in any case.
At present it seems that, at least in the Seattle area, Garmin is dominating
the market. Among Garmins, I would say that I can’t see a good
reason to buy a model other than the Geko 201 or the basic eTrex.
Frequent problems and puzzles
After you’ve learned what all the screens on your receiver are
telling you, after you’ve mastered its manual, you will probably
find that its behavior is still at times puzzling, idiosyncratic, or
downright enigmatic. This all-too-brief primer discusses some of the
most puzzling or most important problems you may experience.
1. The batteries drain too fast.
They probably won’t last as long as advertised. Although it is
good to use NiMH (nickel metal hydride rechargeable) batteries, understand
that their life is usually less than that of alkaline. In cold weather
either keep your receiver warm or use lithium batteries. Don’t
use the backlight or alarms unless they’re really necessary. Avoid
certain tasks, such as frequent rescaling or redrawing of the map screen,
although that computation probably uses negligible energy when compared
with radio signal processing. Use “battery saving” or “power
saving” mode whenever possible. Turn off the receiver when you’re
not moving, for example in camp or during a lunch break.
2. When I’m transferring waypoints between receiver and computer,
the coordinates of the same waypoint come out different.
First, be sure that both your computer program and your receiver are
tuned to the same datum, e.g. NAD 1927 (CONUS) or WGS 1984.
Otherwise, the most likely reason is the use of the wrong datum for
transfer. Even if you have both your map software and your GPS receiver
set to the same datum, e.g. NAD 1927, you may get wrong coordinates
after export or import because the internal format for storing data
is in another datum. Often WGS 1984 is what’s wanted (yes, even
though both software map and receiver are tuned to something else).
Sometimes, but not often, either the GPS manual or the map software
manual will help. In any case, try a different transfer datum.
Another possible reason is that the software GPS device setting is incorrect.
Most map application programs offer a menu of makes and models for GPS
data transmission (waypoint import/export). It is important to be sure
that your software transmission choice matches that that you’ve
selected for your receiver. In some cases, choosing “NMEA”
in both the receiver and software interface menus may help.
3. The displayed altitude is wrong (or frozen or wobbling erratically).
If your receiver is ranging (calculating distances from) only three
satellites, it will be in 2D (two-dimensional) mode, and cannot calculate
the altitude. The receiver will usually tell you this, somewhere, somehow,
but perhaps not so emphatically as you might wish. Even if it is able
to range more than three satellites it may remain in 2D mode if it determines
that the geometric configuration of the satellites is not good enough
to support a full 3D solution.
4. It worked fine in the morning, but when I returned to the trailhead
it failed to track properly. (Or, it couldn’t fix a location on
the way out, but did fine on the return.)
The satellites are always moving, changing position in the sky. Particularly
if you are in marginal GPS terrain (valley, cliffside, forest, northern
slope) you may find extreme differences in behavior at different times.
Because the orbital parameters of each satellite are available to the
public it is possible to forecast the GPS weather minute by minute with
excellent accuracy, but I’m not aware of any off-the-shelf software
that will do this for you. The succinct answer is: GPS is to be used,
not relied upon. Know where you are on your map at all times.
5. How does the thing work?
It’s a miracle.
6. Where can I get further information?
Lawrence Letham’s
popular book, GPS Made Easy, published by The Mountaineers Books and
available, usually, in the clubhouse bookstore, is fine, although very
basic. Web sites I
have found useful include:
http://www.colorado.edu/geography/gcraft/notes/gps/gps.html
http://www.colorado.edu/geography/gcraft/notes/coordsys/coordsys.html
http://www.colorado.edu/geography/gcraft/notes/datum/datum.html
http://www.colorado.edu/geography/gcraft/notes/mapproj/mapproj.html
(for UTM)
Editors
note: Wilderness Navigation by Burns and Burns (Mountaineers Books)
also provides some introductory material.
Software that will probably
(but be careful) link USGS maps to your GPSer by cable includes:
(1) 3_D Topo Quads®: http://www.delorme.com/quads/default.asp/
(2) All Topo®: http://www.igage.com/
(3) Terrain Navigator®:
http://www.maptech.com/land/terrainnavigator/index.cfm?infopg=buy
(4) TOPO!®: http://maps.nationalgeographic.com/topo/
Metsker may have some of these loaded onto a PC for customers to drive
before buying.
(5) OziExplorer®: My personal favorite. See below.
If you really like to buy stuff on the Web, you might try:
http://www.gpsnow.com/topomaps.htm
Other sites from the same vendor sell other nav products. I don’t
recommend this, and I know other competing sites exist that, for all
I know, may be better. Remember that you can get a member discount on
TOPO! at the clubhouse bookstore; however, I’m not recommending
TOPO! over its competitors, either.
For the adventuresome: all of the above programs suffer from one huge
drawback: they sell by the state (or small region, such as southern
New England), and they demand that you use their scanned maps on CDs.
So they can get expensive. A program that works on any e-map is OziExplorer
at http://www.oziexplorer.com/
; look also at the add-on OziExplorer3D. This will be harder to use
because you have to do something to get your map into the software,
but it does pretty much what the four programs listed above will do
(and quite a bit more). If you decide this is for you, note that in
a great many states USGS e-maps are available for free download; send
me an e-mail if you’d like to know some of them. For Washington
state, see a Tip Sheet at The Mountaineers’ Seattle navigation
committee Web site.
Good luck, and enjoy your GPS moments.
©Bill Fortney 2003-2004: BillFortney@aol.com -- Not to be reproduced
in whole or in part for any commercial purpose. Personal use by individuals
permitted, but redistribution is not permitted (you can point people
to this web sight though).
|