Map, Compass & GPS

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

Monday, May 6, 2013

GPS Error part II

There are a few other techniques that I use to get ready to navigate with my GPS receiver.

While driving to camp, turn on the receiver and place it on the dashboard. If the GPS hasn't been used for several months or if the user has traveled a great distance since last use the unit needs to initialize and update satellite data received from the GPS constellation. If that is not possible, allow the receiver to process satellite data for 10-15 minutes in an area where the sky view is open and not blocked by terrain or forest canopy.

Second, give your receiver the time to do it's job, especially with older receivers. For example, with an older GPS (my 10 year old Garmin 12CX) before marking a waypoint I will ensure that at least 4 satellites are being tracked and that the horizon isn't completely obstructed by canopy. While my friends might have been able to mark waypoints considerably faster, I am going to give mine the time to accomplish the task. I will evaluate the estimated position error and if the value is getting smaller I will just wait until it steadies up.

Third, I tend to navigate through the backcountry with my GPS powered up, all day, during a day hike. This allows me to record a track and keeps my position data current. Should I be hiking the length of the Pacific Crest Trail battery consumption would be a concern. That said for my long day jaunts battery conservation isn't really an issue to me.

Older models and those without an electronic compass require motion to develop heading and bearing data.  For example, when returning to a waypoint/destination, take a few steps and observe the display changes and adjust as necessary.  Once the GPS has settled on the correct bearing to the waypoint use your compass to back up your navigation.

Remember to calibrate the electronic compass each time batteries are replaced.

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