Checkout Chapter 22 in the All Topo
Training video for triangulation examples:
[ Training
Video: Click Here! ]
Consider a forest fire burning some distance away. You
can see the smoke, but you have no idea how far away the fire might be. If
you have a GPS and a compass you can quickly determine the fire's
location:
1 From the first place you can see the fire, take a
GPS reading and a compass bearing. Make a note of the bearing and your
GPS location:
40° 51' 13.81" N, 109° 5'
3.90" W
97.5° magnetic north
2 Drive to a second location, far enough away that the
compass bearing changes appreciably, again note the bearing, and GPS
location:
40° 51' 13.81" N, 109° 2' 36.65" W
223.5° magnetic north
3 Finally, display the 'Triangulation Tool' by
selecting 'Tools: Triangulation…' from the main menu:
Enter the two base coordinates and angles, selecting
the correct North Reference (Magnetic North).
All Topo will compute the fire location and place a
temporary marker at the intersection. Press the thumbtack next to the
triangulation point to add a user annotation at the intersection.
It is important to choose observation points that have a
large difference in bearing to the target, and to use a quality compass in
a non-magnetic environment. In this example, a 2 degree error in the
bearing results in a ¼ mile error in the projected fire location. For
this reason, the use of a quality sighting compass like the Brunton
Sightmaster is highly recommended.
The Brunton Sightmaster (SM360LA)
With some practice, you can quickly take ½ degree
repeatable bearings with this compass. Since All Topo automatically
adjusts for declination, you won't need to worry about computing
declination (or in the worst case setting the declination backwards!)
back to All Topo Maps
V7 info
