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GPS units can show you the way
Handy locating devices are “incredible technology at an amazingly low price”

By Keith Ridler
The Bulletin
, Thursday, May 9, 2000

For outdoor adventurers, the $100,000 question has always been: "Where are we?"

These days, technology has reduced the cost to just north of $100 for Global Positioning System (GPS) units.

"They are incredible bargains," says Bob Speik, a local mountaineer and backcountry adventurer who gives GPS classes. "They are incredible technology at an amazingly low price."

Many trail books, mountain bike books, and others use GPS "way points" to mark significant locations, like turns in the trail. A GPS user can also store his or her own way points in the GPS for use at a later time, such as the location of the vehicle, or the route for returning to that secret, hard-to-find fishing spot next month.

A GPS unit can also give the elevation at a particular point, download computer software with maps, and be programmed to mark the way before the user heads into the backcountry.

The hand-held GPS units seem ridiculously small and lightweight for all the tasks they are asked to perform … until you realize they are backed up by a network of 24 satellites (12 in each hemisphere at any one time) orbiting about 12,000 miles above the Earth.

Twenty-four is the most commonly cited number, though there are apparently spares also orbiting the earth.

"There may be 34 or 64 up there. We don't know," says Speik. "It is a Defense based Navigation System."

The satellite network was designed and built by the United States to help fighting forces pinpoint their own as well as the enemy's location, and so there is a degree of secrecy and some contradictory information about some of the details of the system.

However, the system was made available for public use in the early 1990s, but with "Selective Availability" that purposefully gave inaccurate information to privately-owned GPS units, misdirecting them by introducing a wandering error of up to 600'.

On Monday, May 1, 2000 that purposeful misdirection was eliminated, so that private GPS users can expect amazing accuracy to within a few meters. Military uses remain more accurate, to within inches. But for private GPS users who aren't concerned, for example, about directing a cruise missile into the mouth of a small cave opening, the accuracy is astounding.

Speik has even experimented atop Pilot Butte, testing the accuracy of his Garmin Etrex GPS on some 25 different occasions. The GPS has every time been within six feet of elevation and 15 feet laterally, Speik notes, comparing the GPS readings to the United States Geological Survey marker on the butte.

"That's mind-boggling accuracy," says Speik. "And the GPS doesn't know it's on Pilot Butte. That's anywhere in the world. It's that accurate anywhere in the world."

The Garmin Etrex is the cheapest GPS on the market, usually costing about $120. The more bells and whistles you buy, the pricier a GPS becomes, with some costing more than $500.

But what all recent GPS units have in common is the way in which they pinpoint locations. That means recent GPS units are equally accurate, no matter the cost. That's not to say some extra features that cost more might not be useful, but you don't get better precision by spending more money.

"I've got seven different models," says Art McEldowney, a former telecommunications officer with the U.S. Department of State and a backcountry enthusiast who also gives GPS classes. "They all have the same degree of accuracy. So if you spend a $109 on one or $509 on one, you get the same degree of accuracy."

"People think you get more accuracy if you pay more," says Speik. "That's not true. All a GPS is is a radio receiver, a little CPU, a quarts clock and a little dedicated software."

A GPS unit works by receiving signals from the satellites overhead, usually capturing six of the signals in open terrain, and sometimes more. It then performs a series of mathematical calculations based on the positions of the satellites and the amount of time it takes the signals from the different satellites to reach the GPS unit.

After completing the number crunching, it displays two coordinates that can be located on a map. Different maps use different systems so a GPS unit user must make sure the GPS unit and map are using the same datum.

Many maps use the Universal Transverse Mercator (UTM) Grid. After the GPS unit displays the UTM numbers, those numbers are found along the edges of the map. The point on the map where the numbers intersect is where the GPS unit … and the person using it … is located.

"It gives you numeric coordinates, which is the same as saying Hwy 20 at 27th Street" notes Speik.

Another handy function of a GPS unit is the "go to" mode. A hiker who wants to return to his or her vehicle … which has been marked with a way point … can than hit the "go to" function of the GPS unit. The unit will then display the direction and distance to the vehicle. The users can then use their compass and map to "go to" their rig.

GPS units can even be downloaded with USGS topo maps, and the unit will display a map showing the terrain between the current location and the vehicle.

"Mine has two-thirds of the state of Oregon loaded into it," says McEldowney.

You can also get GPS units that display sunrise, sunset, moonrise, moonset, moon phase, the best times for hunting and fishing, electronic compasses, and more.

Before getting carried away with the abilities of a GPS unit, Both Speik and McEldowney point out that they are simply another backcountry tool along with a map and compass. A GPS unit with dead batteries, or one at the bottom of the river, won't be much help.

"I'm not aware of any GPS manufacturer that will stand behind their product as a primary source of navigation," says McEldowney. "It should be used as an augmentation tool."

GPS units have become so inexpensive and popular that recently they have led to a new sport called "Geocaching." A Web site ( lists hints and coordinates for locations for cached items. A person with a GPS unit can then go out and try to find the
item. There are 164 cached items in Central Oregon, some even in Bend.

Both Speik and McEldowney, for a fee, give GPS instruction to groups and individuals. Speik can be contacted at 385-0445, and McEldowney at 385-6789.

See also:
Geocaching in the news
Backcountry navigation classes