Wednesday, October 22, 2014

How to improve the accuracy of your GPS on a day hike

GPS devices can have measurement errors of  up to 25 feet.
Photo courtesy of larsipulami / Photoree.

Seek clear skies,
use AVG function

A number of day hikers have taken to using a GPS device when hitting the trail. While that’s always risky – batteries can go dead or the electronics could be dropped and cease to function – so long as you have a topo map and a compass for backup, using GPS to navigate is perfectly fine.

As with guestimating where you are on a map, not all measurements on GPS are entirely accurate; indeed, a GPS device can be up to 25 feet off. This is problematic should you become lost.

Fortunately, you can take a few steps when day hiking to ensure you get the best reading possible.

Clear view of sky
Stand in an open area so that the GPS device can receive measurements from at least four satellites. The more satellites the device connects with, the more accurate the reading will be. Rock overhangs and trees can diminish those signals and result in a poor measurement.

Use the averaging function
If your GPS device has this option, you’ll find it beneficial. During the hike, stop for several minutes and have the GPS device take a half-dozen or more measurements. The device then will average them to determine your location.

Smaller beats larger
The larger the number on your device’s EPE (Estimated Position Error) readout, the less accurate the measurement. If you take two different measurements and can choose between a smaller and larger number, go with the former.

Don’t rely on return measurements
Thanks to the ways GPS devices remember waypoints, the measurement error for returning to a marked waypoint will be greater than the error when you determine your absolute location. If you find yourself in a situation where you must choose between two conflicting measurements, go with the absolute over the return to a marked waypoint.

Learn about trail guidebooks available in the Hittin’ the Trail series.