Posted by: Dan Sprague | December 2, 2011

How GPS Track and Chart Plotters Work.

A GPS uses a global positioning satellite to tell where you are located on the earth. A GPS receiver can give you your position in latitude and longitude on a map or chart, and the accuracy can be within a few feet. By using the position you are at as a starting point, and imputing a waypoint (a latitude and longitude) of where you want to go, the GPS can point you to that location. You can plot a course that you wish to take by imputing in a series of way points. The GPS can point you to each way point, and when you get to that point it can point you to the next waypoint.

As an example, with a GPS, you can use your dock as a starting point waypoint for trip. By imputing a waypoint in at each place you turn, you build a series of points that form a tack or plot line of the course you took. On your way back the GPS can point you to each waypoint in reverse order and point you to the next point, getting you back to the dock on the same course you went out on.

A GPS can make navigating to and from place to place safe and easy. If you plot your course there by imputing the waypoints into the GPS that you have taken from a chart, before you head out, it can point you there and get you back. Or you can put them in as you go to get a course you can follow back.

GPS track plotters and chart plotters do the same thing, but with many automated features. They do much of the work for you. Some have a display that shows a line or road way with a pointer on it. The roadway is pointed to the waypoint you are headed for and the pointer points in the direction you are going. You just turn your boat heading back and forth to stay on the road.

A chart plotter doses the same thing but also shows a chart and where your boat is on the chart. A chart plotter can be more useful to a boater in that the chart can show hazards in the water, shallow water, and land marks that can make navigation easier. Some units come with charts already installed, other require you to download charts of the area you want into them. The amount of detail on charts a GPS uses can very basic to very detailed.

Both track and chart plotters can automatically remember the course you follow without having to input each turn manually. They can also tell you what speed you are going, the time it will take to get to the next point, estimate the time it will get to your end point and all sorts of other neat things. Your VHF radio and GPS can be connected for DSC (distress call) functionality. This gives the Coast Guard your exact location, identity and boat information automatically, if you make a mayday call.

You still need to know how to do basic navigation even if you have a GPS. The GPS system can be disabled in times of war or a disaster or national emergency. This is not likely, BUT!

A compass and chart can replace a GPS, but a GPS should not replace your boat compass.

These units are often multifunctional, a path to your destination, a chart of the area, a fish finder and depth finder are just some of the things these units can do.


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