Why does a marine Global Positioning System have an altitude setting?

Answer 1

Ha! Good question. There is no reason for an altitude readout on a marine GPS, except for the possibility that the GPS might have been designed as a dual-purpose or cross-purpose unit. A hand held GPS can easily be used on a boat, for hiking or geocaching, or in an airplane. A fixed unit could be used on a boat, in an airplane, or in a car. Any of these non-marine uses could have a need for an altitude readout.

As the response below suggests, there may be a need for the equipment to include altitude calculations in the resolution of GPS position. However, altitude information for users of marine GPS units have little if any need for altitude information.

There is a reason.

GPS's altitude measures the users' distance from the center of the SVs orbits. These measurements are referenced to geodetic altitude or ellipsoidal altitude in some GPS equipment. Garmin and most equipment manufacturers utilize a mathematical model in the GPS software which roughly approximates the geodetic model of the earth and reference altitude to this model.

Like when one uses a sextant, altitude is important to work out the distance to the horizon and hence make navigation and more rightly ocean (non-pilotage) navigation possible.

I hope this gives you an idea of what the altitude figure on your GPS means.