[Philmont]: GPS

In my opinion, UTM is far easier to use than Degree/Minutes/Seconds (or
decimal degrees). UTM provides a simple grid and the coordinates are whole
numbers. Since the numbers represent meters it is very easy to determine
distances.

With UTM you can quickly locate coordinates on a map. Drop the three least
significant digits of the coordinates to identify the grid cell. Use the
three least significant digits to locate the point within the cell. I've
found that youth can easily learn to use a GPS with UTM. They actually
begin to appreciate what they learned about coordinate systems in math
class!

Most new maps have a UTM grid. Older ones have ticks along the borders, so
you may need to draw the grid lines yourself. Another important point is to
make sure your GPS is configured for the correct datum of the map (i.e.
WGS84 or NAD27) you are using. If you have a mismatch, your points will be
shifted, sometimes by hundreds of meters. Likewise if you pickup a set of
waypoints, you need to know what datum it is in.

I have found that since the intentional degradation of the GPS signals was
discontinued in 2000, that most waypoints marked by a GPS are very accurate.
That is, the coordinates can be given to someone else and will lead them to
nearly the exact spot. This is one reason Geocaching has become so popular.

However, determining coordinates of an object from a map is different. The
map scale may not provide great accuracy. Objects, particularly those man
made, are not always shown on a map in the exact location. In addition, for
remote areas USGS maps can be very old (40+ years) and things change over
time. Roads and trails may be rerouted, manmade things move or come and go.

 -- Jeff

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Jeffrey W. Knoll
Troop 513
Crew 124
Grand Canyon Council
Phoenix, AZ

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Received on Wed Mar 12 16:54:45 2003