Map, Compass & GPS

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

Sunday, May 4, 2014

GPS - Returning To A Destination

The hike into the backcountry has come to an end.  Now it’s time to return to the trailhead.  By selecting “Find” or “Where Is” the GPS receiver provides direction to the trailhead.

Before returning, the hiker should review several GPS navigation considerations:
      The Electronic compass:  It must be calibrated after each battery change.  If the hiker doesn’t remember doing this, calibrate the receiver.  Bearing information will be more accurate by several degrees.

Figure 1.  GPS Compass display.  The bearing to the destination is 298°.  The hikers heading is about 115°.

·         Distance information:  This data (e.g., 10.2 miles) is line of sight or more commonly, “as a crow flies.” The GPS receiver doesn’t take into account topography and detours that may be needed.  Thus, a distance of 10.2 miles may really be 11.2miles or more at the end of the hike.

·         Bearing: Make sure that bearing information is presented in degrees and not “cardinal letters” such as NNE (North North East).  The hiker’s compass provides direction information in degrees.  When aligned this keeps navigation simple; both compass and GPS complement each other.  Make this change by adjusting the compass setup.  

As shown (figure 2 above), the GPS provides direction (298°) and distance (10.2 miles) to the waypoint.  The direction is the “Bearing” to the waypoint.  The red arrow and digital read out provide the return direction to the waypoint, in this case is 298°. (The red arrow points the hiker to the waypoint.)  As the hiker moves down the trail, expect the receiver to provide continuous updates to the selected destination.  Movement on the will may cause the red arrow to move and the digital information to change too.

Note that the return direction (Bearing) to the original waypoint may very likely be different than the heading as the hiker moves down the trail.  Heading is the hiker’s direction of travel, his path through the backcountry.  In the example (figure 2 above) the heading is 115°; the direction of movement.  Later, as the hiker moves directly to the waypoint, both the bearing and heading may be the same.

·         GPS Map Page: Select the map page.  Use this page to corroborate the electronic compass information.  

In this view, the wide blue line is the GPS track; the hiker’s historical path through the woods.  The exaggerated black triangle points in the direction of travel. (The other red and brown lines are logging roads.)  To obtain this type of presentation the GPS has been left on capturing satellite data during the entire hike.  Using the black triangle, the hiker can follow his movement down the trail to the waypoint destination such as “CAMP” at the bottom right of the screen.

·         Bushwhack:  Occasionally the hiker may elect to bushwhack from a current position to a new destination.  The hiker should consult the map to assess the overall big picture to determine if the route is safe, find and identify natural obstacles and evaluate terrain.

·         Map and Compass:  Don’t leave these important tools stuffed away in the pack.  Practice with them during the hike.  For example, use the map and compass to orient the map to get the general lay of the land.  Use the compass to further evaluate the bearing to a destination.  For example, the GPS’ determines that the bearing to the trailhead is 298°.  Use the compass to sight a bearing of 298° and follow the compass rather than the GPS’ electronic compass.

Navigation is not hard but it takes practice and repetition.  Don’t assume you will have the same visual landmarks on the return trip.  A change in weather (fog and snow) can increase the complexity of your navigation.  Practice and experience significantly helps develop confidence in the hiker’s skill level and equipment.

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