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68 SporTrak Color GPS Mapping Receiver
Appendix
Compass
The SporTrak Color includes all the features found in all of the SporTrak mapping series
of GPS receivers along with a 3-axis electronic compass, a barometer and temperature
sensor.
The following text provides you with some information about some of the navigational
terms that are used with the electronic compass.
Heading vs. Bearing vs. Course Over Ground
The SporTrak Color adds Course Over Ground (COG) to the list of data parameters that
you can select for the customizable fields that are displayed on the navigation screens. The
SporTrak Color also uses COG on the compass screen to provide you with additional
information that will assist you in navigating to your desired destination.
Heading, in the SporTrak Color, is not computed from the GPS information as it is in the
other SporTrak Color products, but rather it uses the electronic compass to determine
which way you are facing.
The following is a brief description of how the SporTrak Color interprets heading,
bearing, and COG. If you already understand these terms you can skip over the following
section.
Heading
Heading in the SporTrak Color is the direction that the antenna (located at the top of the
SporTrak Color) is pointing. To get the best representation of your heading, you need to
hold the SporTrak Color with the antenna pointing in the direction you are travelling.
Holding it at an angle, left or right, will accurately display the heading of the receiver, but
it won’t be a true representation of your direction of travel. (As you will see next, COG
provides a true indication of your direction of travel, regardless of which way the SporTrak
Color is pointing.) Heading is displayed all the time.
Course Over Ground (COG)
COG is the direction you are travelling. With the SporTrak Color held directly in front of
you, you would think that heading and COG would be the same, but that is not always
the case. Boaters are quite familiar with heading and COG being different due to tides
and current.
An example of that would be a boat travelling along with a
heading of 0°. At the same time, there are currents in the water
pushing the boat to one side. This would cause the boat to drift
off course in the direction of the current. How much it moves
depends on the speed of the boat and the force of the current.
In this example, the resulting COG or direction of travel is 15°.
COG
15°
Heading
0°
Current