GPS Navigation – 3D Mode

GPS navigation systems are amazingly useful devices for any wilderness or outdoor activity.

But like any complex electronic instrument there are specific technical features which must be mastered, and a learning curve before one is fully proficient in their use.

One important feature of many portable GPS navigation units is what is known as “3D Mode”. Many portable navigation devices display when the unit is in 3D mode, or in 2D mode. 3D Mode has the fairly simple definition of when the GPS navigation system is picking up signals from a minimum of 4 navigation satellites. When it is picking up signals from only 3 satellites it will display as being in 2D Mode.

To plot a position, the navigation software in the GPS unit needs three signals from 3 different satellites. However with only 3 signals it cannot get a fix on its elevation (thus it is plotting in 2 dimensions). The result is that the position displayed can be off by as much as a mile. With signals from 4 satellites it can use any 3 signals. With 4 satellites it has 3 different combinations of signals. With each additional GPS sat nav signal the accuracy increases exponentially.

With multiple combinations of signals, the GPS unit can get a fix on its elevation, therefore is plotting in 3 dimensions, and is in “3D Mode”.

Many portable navigation systems display when it is in 3D Mode or 2D Mode, others do not. For instance with a Garmin GPS navigation unit, you must verify that you are receiving signals from 4, and not just 3, satellites.

With any mobile navigation device, always make sure you are in 3D mode, or visually verify you are tracking a minimum of 4 satellites, before you assume you’ve got an accurate report of your location.

One last tip for increasing the accuracy of your satellite navigation system is to use the “Averaging” function, if your unit comes equipped with this. Look for this function (“AVG”) on the “MARK” page. For this function to work, after you activate it you must stay in one location for a few minutes before continuing.

The author, Mike Wreggitt, has had a lot of experience in “old school” wilderness navigation using a Brunton compass, and has become an ardent fan of portable GPS navigation systems. Learn more about GPS navigation at http://GpsForHiking.net.