GPS and County Highpointing
*1 Original content by Glen Bock
*2 Addendum by Gordon MacLeod
*3   wordsmithed by Adam Helman
What is GPS and how it Functions
GPS is a satellite-based system for determining with great accuracy the
position of an earth-based object. Originally developed for the United
States military, GPS (Global Positioning System) consists of 24 satellites
that continuously transmit timing information. An earth-based receiver
may use this data to triangulate its position based upon the simultaneous
reception of either 3 or 4 signals from as many satellites. Three signals
are sufficient to determine latitude and longitude with high accuracy and
precision - while four signals are required for the additional determination
In greater detail,
the satellites send out time signals and the GPS unit receives these.
The time it takes for
each satellite's signal to be received is recorded, thus
generating a sphere of distance from each satellite.
The GPS unit lies at the intersection of these various spheres.
A minimum of 3 signals are needed to be "in view", 4 is best, but barring
any problems say, in the bottom of a steep valley, the GPS unit is likely
to "see" 7-10 GPS spacecraft, so allowing the GPS to select the best
geometric set to use in triangulating its location.
The satellite-borne clocks are accurate to one-billionth of a second (light will
travel about a foot in that amount of time), and the resulting
accuracy of the time signal method (as presently available to civilians)
is around 30 feet (pretty good). Many GPS units will also
allow "time averaging" of a location allowing greater confidance in a
location by taking multiple "readings" of a location AND allowing the
constellation of spacecraft to change - so allowing many differing geometries
to be involved in solving for the location.
If for example you are 100 feet from a particular fencepost (GPS
satellite 1); 200 feet from a large rock (satellite 2);
56 feet from a treestump (satellite 3); and 30 feet from a
squirrel (satellite 4), you can determine your positions fairly well.
GPS in the Context of Outdoors Activities
GPS may enhance the experience and record
keeping of many outdoor activities. A GPS unit will let you mark, and
record a timestamped waypoint of anyplace on the surface of the earth.
Record a few, or as many as you wish, of these waypoints and you then
have a highly accurate record of any outdoor excursion, including
direction traveled, time to travel each and every leg, and even average
speed (some devices will record instantaneous speeds as well).
What can be generated is a record of locations that the hiker
passes through. The device may be used passively to document a journey
by placing it in a backpack and allowing it to record points encountered.
Alternatively, GPS may be used actively,
allowing the user to load a known location from either a map or
location database. In active mode the GPS unit directs, in a rudimentary way,
the user from one point to another, in some cases giving distance,
bearing (magnetic or true) and even time of arrival at the location at
String many significant "travel points" together and you
can generate a route that the device will actively tour you through,
telling you where and when, and in what direction to turn.
To attain a specific geographic location (aka County Highpoint),
it would be good to create a starting list of waypoints of attainable locations
enroute to the desired location.
In the case of a highpoint that is a true mountain summit,
the attainment of the highest elevation may be obvious to even
the most casual observer. However for highpoints with
shallow terrain, and little in the way of obvious detail,
a GPS unit may provide increased certainty that the
attainment of a grey-area highpoint is realized.
Even if later the exact identity of a
highpoint is disputed, there will be an accurate record of the location
attained, with time and date, and locale recorded to a typical accuracy
of tens of feet in latitude and longitude.
Practical Use Of Latitude/Longitude and GPS Technology
In Colorado, many of the county highpoints are easily located, high
mountains or obvious summits. The highpointer
may record any additional details to a high degree of accuracy (trail
intersections, boulders, trees, dangerous areas) and then explicitly and
accurately communicate those locations, routes and details in
numerical terms. These numbers can then be used by others to
enhance their own personal exploration and attainment of these points (or
not if the user wants to explore on their own). This allows for
greater confidance, situational awareness and knowledge about the
geography, topography and trailfinding.
Debates and useful
conversation/comunication can only be enhanced by the use this accurate
method of presenting locations, times and bearings. Many GPS units
support the direct linking of a computer to the onboard memory,
allowing the user to actually "save" their trip's waypoints in a format
that can be labeled, organized and archived. These saved files can then
be shared, much like and along with the trip reports that are so much a
part of our hobby.
Imagine going to a highpoint in a state you have
never traveled through with the confidence that you can directly locate
the EXACT legal parking lot, and travel along a known safe route to a
point that someone else has painstakingly mapped, plotted, researched and
recorded. If Mallory had such a tool we would know with accuracy his
fate and achievements.
Add to this the fact that many county
highpointers just plain LOVE maps and mapping - and the interface of computer,
GPS and maps is complete: one may a trek up a mountain, attaining
the highest point and then return home, link the GPS unit to
a computer and thereby generate a map with the exact route
you hiked emblazened in red (or whatever color you choose) directly
traced onto the USGS topographic map. It would include times of every
point along the sojourn.
One may even record exact locations where pictures
are taken so bearings, distances and features could be exactly
identified after the hike without having to distract one from the true
beauty of the trip. Or one can do it all on the trip, accurate
triangulation of unattained locations being simple with the recording of two
waypoints and their attendant magnetic compass bearings, allowing the fun
of the trip to last longer as you review the trip at home.
GPS devices are becoming inexpensive that will allow the input of a
target location. In the future these recording devices may become more
useful than even the maps used for hiking. In fact one
can add wonderful hiking graphics to trip reports - so leaving very
little ambiguity to one's achievements. Imagine downloading a map,
waypoints (input into the GPS unit via computer) and
actual pictures of the hike (linked to the map). It affords a capability
of planning and forehand knowledge that Lewis and Clark would find amazing!
"Disputed highpoints" may now be discussed with
certainty and exactitude hitherto impossible, conveying to anyone
the exact location one is talking about (to a reproducable accuracy of 20 feet).
There is also the safety factor of locating shelters (natural or manmade)
that you have never seen. Weather can change quickly, and having the
confidence to locate a contingency shelter quickly without getting lost in
the adrenalin of the moment may spare individual discomfort and injury,
and at the very least make the trip much more enjoyable.
Unique features of very small scale can be located and re-visited by others.
For example, GPS technology has spawned a completly new and very
complimentary hobby of geocaching wherein "presents"
are hidden at unique locations all over the United States for the curious
to find, be it with GPS or standard map and compass - so enabling one to explore not
only the highest points, but also the places that someone has found
beautiful and special.
I recently ferreted out a 10-inch square
tupperware container that had been hidden by someone I don't even know
(oddly enough the day before) in a place I had never considered going to.
Using only a GPS and a wonderful day I was able to locate the container,
hidden under a fallen tree and made a log entry. There are literally
hundreds of these caches all over the USA, placed by people that want to
have fun. I'm sure this skill will have great useful influence on the
also developing hobby of county highpointing.
Perhaps soon people will distribute exact routes, turns and
switchbacks, elevation gains and bearings for every highpoint.
Together we can generate an amazingly useful database that will increase the
efficiency, safety and legality of our chosen hobby.
"The more you know about your surroundings, the better you appreciate
them and remember them".
Tips and Suggestions
I personally find DD.ddddd format the easiest, but most people are
familiar with DD.MM.mmmm and it's the default format of most GPS units.
The DEM elevations are derived using USGS 1:100,000 Digital Elevation
Model and are to be taken with a grain of salt, particularly for those
locations that the elevation is known well.
You can often get a cigarette lighter power plug allowing the recording
of the entire road trip to the trailhead too. TOPO software will even
allow the recorded route to be "profiled" or the elevation gain and loss
plotted out along the drive/hike. One may determine
not only average speed of a hike, but also
elevation gains and rates of elevation gain at
various parts of the trip. This method is FAR superior to my recording
An additional use for a GPS recorded
waypoint (or the map-read ones included) is that by going to
you can enter in the latitude/longitude and (if they
are in the database) see a USGS flyover view of that particular location
(1 meter resolution in most cases). I did a hike in the Canyonlands a few
years ago and was able to plot the exact hike I did from the recorded
waypoints in my GPS I took in the field, AND even located a particular
boulder we camped next to (and the nearby arroyo) that I took pictures of
on the ground in the USGS flyover. It definitely added a HUGE dimension
to the experience: being able to print out the hiked trail in map format AND
include a flyover photo in my personal trip report!!
There is a free piece of software that the
Geocaching people are using to save and read the waypoints from/to their
GPS units and they can then send the waypoint files to each other (or post
them on the web) that will work with virtually all computer-interfaced
GPS units on the market. It is downloadable for free from the
GPS is a wave of the
geographic and location future - it never hurts to know exactly where you
are at any given time. I used my GPS to record hikes, and in one case a
12 day canoe trip in the wilds of the Missinaibi River in Canada, I'll be
able to convey exact campsites to anyone in the future using the recorded
waypoints I made from inside my tent every night before I went to sleep
(only used 3/4 the charge in one set of batteries too!)
If more people start doing this, many a hiking-related hobby will be advanced
through rapid, accurate dissemination of exact locations, terrain and
bearings to features, peaks and trailheads.
It may be as common as having a compass in the coming years. There is also the
ability to interface with internet photographic maps, and TOPOZONE, or
terraserver maps, as well as with standalone mapping programs like Delorme or my
Indeed, with version 3 of the TOPO! software, you can put links directly on the map,
click on a waypointed location and up will pop a picture you took (and saved on
your computer via digital camera or scanner) of that location. Furthermore the
files are sharable! The Colorado set of TOPO maps (7 CD set) is
something like only $100 or $200 - which comes to 7 cents a 1:24,000
quad if I remember right. Finally, the upgrades to the software are amazing.
In a few years you'll be able to generate a relief panorama shot from
any particular waypoint location looking in any direction and SEE what
the surmounding mountains look like using the topographic data. I bet
this will be available off the shelf in a few years to the normal user.
There are some programs out there already to do it, but they are
particularly cumbersome to use, and you need special (expensive) datasets.
This stuff rules!!!
Addendum - GPS Functional Capabilities and Advantages
- by Gordon MacLeod
A remarkable capability for trip planning and field navigation results from the combination of
a high-tech GPS with the capability of receiving both downloaded maps and waypoints generated by map
computer programs. The maps are complete with roads at all levels
of utility (down to four-wheel-drive accessible only), trails, washes, lakes, facilities of
all sorts, peak names, and more. I find that my GARMIN GPS III Plus serves admirably
for the GPS unit, while DeLorme TurboQuads is a good waypoint-generating program.
This capability has been recognized and, indeed, exploited by the marketing
departments of the map developers and GPS manufactures. However I suspect
that most GPS-using peak baggers are not taking full advantage of this
remarkable capability. We certainly use purchased USGS topos; and either download
portions from TopoZone or use TurboQuads
(or MapTech's competitive product) for trip planning.
However, are we downloading waypoints (or even entire routes)
that can be readily created to mark key road or trail junctions,
peak locations, etc...?
The accuracy with which those waypoints match their true topographical location is impressive,
the waypoints having been created by using map programs and then downloaded.
Typically, on a summit with a benchmark, the error between the
waypoint benchmark location and that reported by the GPS unit is about 10 to 20 feet - highly accurate.
On summits without a benchmark, an extra source of error, of course, is introduced
by the uncertainty of identifying the actual high point,
so the error between the waypoint location and that reported by the GPS unit
increases to about 50 to 100 feet.
These figures contrast with the larger errors of 100 to 300 feet that arise from manually
interpolating coordinates from the topo charts themselves, and subsequently downloading
said coordinates into the GPS unit.
Note that the aforementioned error between the downloaded waypoint
benchmark locations and the GPS-reported actual positions of about 10 to 20 feet
compares with the GPS unit's calculated 2-summa horizontal position error of typically 10
to 20 feet.
Note also that this discussion refers to horizontal
position error and not the vertical position error, which is -- as you are
well aware -- a totally different matter because of the significantly
increased errors arising from the relative geometry of the various
satellites in earth orbit.
Handheld GPS technology moves ahead with significant improvements in accuracy
and in memory capacity since my purchase of a GARMIN GPS III Plus for $400 in 1999.
Although I cannot quantify the improvement in accuracy,
the memory capacity has increased from 1.44 MB in the GARMIN GPS III Plus
to 19 MB in the current top-of the-line GARMIN GPS V Deluxe model for $500.
A 1.44 MB memory accepts a download of detailed road information plus
data for about five average-size Arizona or Nevada counties. I estimate that the
19 MB memory could accommodate all of Arizona and Nevada at the same time - a noteworthy feat.
Addendum - GPS Functional Capabilities by Example
- by Gordon MacLeod
Appendix - GPS Rules
Example one: In DeLorme's TopoQuads program, you can select, generate and download
a waypoint for a key road junction, such as the point where you plan to leave a gravel road and access
a secondary road. As you approach the road junction identified as a waypoint in your high tech GPS receiver,
you will see a cursor, representing your vehicle, on your GPS display moving towards
the road junction in real time. At the junction itself, you can expect to be within 20 to 50 feet.
This account generalizes to all waypoints and applies to four wheel drive road forks, trail junctions
etc...; in daylight, at night, in whiteouts - you name it.
Example two: You just took the right fork at a trail junction, but things just don't seem right.
You wonder, did I turn at the correct junction? Your GPS unit can determine within
minutes your position relative to the waypoint marking the correct junction, under all conditions.
Furthermore, the GPS unit determines how far you are off-route and in what direction, guiding you
to the waypoint itself.
Example three: You didn't get around to making a waypoint for a key road
junction and you are wondering whether that four wheel drive road forking to the right
is the one you should take. You were savvy enough, however, to have
generated a waypoint for that county high point you're after. The GPS will
tell you how far you are away from the high point and its bearing. The bearing
by itself is sufficient to locate yourself on the map,
provided the high point is on the map. If not, use your compass
to determine whether that bearing has you looking at a likely county high point.
This ability of the GPS unit to determine the distance and bearing to a waypoint is profoundly valuable,
and undoubtedly one of its most useful contributions to navigation. So, a cardinal rule is:
At a minimum, while at home make waypoints for the summits that you plan to climb with a
favorite map program. Making waypoints on-the-road is not advisable, as this will
embroil you in the details of UTM (or latitude / longitude) coordinates and is
error-prone if you are not mathematically inclined.
Example four: Is it not satisfying to know that you are within 10 to 20 feet of the
county high point you were seeking when sitting on the presumed high point eating your lunch?
Example five: If you have the GPS unit "on" while driving, it automatically generates a
trail of electronic bread crumbs that mark your route. If you are uncertain of which forks
you took, or if you are in a whiteout, simply reverse course by following the
bread crumbs. Neat, don't you think?
The GPS spacecraft constellation cost american taxpayers around
14 billion dollars. Once you buy a GPS unit you can use the system as much as you want.
No access fees or other charges (except for say batteries).
The GPS system can be augmented (for civilian users) to a greater accuracy by
using differential GPS, allowing accuracies of a few inches. Military
devices allow centimeter accuracy all the time with no additional equipment,
and use an encrypted access system to allow Milspec GPS devices that
"fell into the wrong hands" to be rendered virtually useless. As of 2001 the
military has never severed civilian access to the constellation (but they
could given a significant need). However nowadays so many devices depend on the system,
it would have to be a serious situation for that to happen.
Appendix - Specification and Use of Datum
- by Adam Helman
It is imperative that the same datum be employed in the GPS unit and the corresponding
topographic chart. For the continental United States the main choices are the NAD27 datum
and the NAD83/WGS84 datum. Failure to recognize this will often result in position errors
of up to 300 meters as shown in Figure 1. In that figure, the absolute differences between
NAD27 and WGS84 coordinates are presented on a 5 degree grid superimposed on the lower 48 United States.
Note how the West Coast suffers the largest magnitude differences.
Figure 1. The absolute difference in NAD27 and
WGS84 coordinates presented as circles of varying radii.
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