Map, Compass & GPS

Map, Compass & GPS
Wild flowers along Fall Creek on the way to the Green Lakes - Oregon

Sunday, April 5, 2015

GPS Error - Part I

Our GPS receivers are very accurate.  What should the hiker do when the information displayed just doesn't look right?

Ever have one of those "GPS days" when the darn thing is providing a bearing that looks way off the mark...."that can't be right?"

Here is the typical scenario:  As the hiker leaves camp he marks "camp" as a waypoint in the GPS.  Throughout the day the hiker maneuvers about the forest and by late afternoon it is time to return to camp.  He selects "find" and calls up the waypoint for camp.  The GPS indicates that camp is two miles out on a bearing of 330 degrees; but that doesn't look right.  The hiker compares the receiver's information with map and compass.  After a bit of analysis the hiker recognizes there is a problem.  What should he do? 

I have a few recommendations to help improve the inaccuracy that the hiker is experiencing.

First, calibrate the electronic compass.  Always calibrate the compass after installing new batteries.  (Check the owner's manual to determine if your GPS has an electronic compass.)

Second, turn off the GPS, turn it back on, select "find" and evaluate the new data to return to camp.  Check the satellite view screen to ensure that at least four satellites are being tracked.  Consider moving to an area that has an open view of the sky.

Third, if the information present still looks in error, take five to ten steps in the direction recommended to see if movement effects the data displayed.

Fourth, open the battery compartment and remove one of the batteries.  Keep the battery out for 10-20 seconds and then return it to the GPS.  Power the GPS back on and repeat the process by selecting "find" to return to camp. 

Lastly, it may be that the saved position of camp was made before a solid satellite lock was achieved.  Compare the saved coordinates for camp with the plotted position of camp.

Usually, these five steps will clear up the issue.

Remember, never leave your map and compass at home.

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