Maps / GPS

GPS Navigation

Below you will find an explanation of some terms frequently used, to help you understand what we are talking about.

Position, Waypoint, Routes and Tracks

Position

An exact, unique location based on a geographic coordinate system. The Position Format is the way in which the GPS receiver's position will be displayed on the screen. It is commonly displayed as latitude/longitude in degrees and minutes, with options for degrees, minutes and seconds, degrees only, or one of several grid formats. When a position is stored in your GPS-device it becomes a waypoint.

Waypoint

Waypoints are locations or landmarks worth recording and storing in your GPS. These are locations you may later want to return to, such as the position of your car. Waypoints may be defined and stored in the unit manually by taking coordinates for the waypoint from a map or other reference. Or more usually, waypoints may be entered directly by taking a reading with the unit at the location itself, giving it a name, and then saving the point. Most GPS receivers have a capacity of 500 to 1000 waypoints.

Some GPS-devices allow you to enter waypoints by referencing another waypoint already stored, giving the reference waypoint, and entering the distance and compass bearing to the new waypoint.

You can also enter a reference waypoint as the "go to" waypoint in the GPS unit to get your bearing and distance off the waypoint. Many devices will also show you Time To Destination (i.e. estimated travel time to the final destination) and Time To Next (i.e. estimated travel time to the next waypoint). An electronic compass in a GPS device allows the receiver to show you an accurate navigation arrow for navigating to the next waypoint even when you are standing still (a standard GPS cannot tell you which way north is when you are not moving). Routes can be compiled by putting several waypoints into the GPS device.

Routes

A route is a group of waypoints entered into the GPS receiver in the sequence you desire to navigate them. Most devices can store between 10 and 20 routes, with around 100 trackpoints per route. Routes and waypoints can be edited and deleted graphically on the map view using the GPS waypoint tool. Whenever you activate a route with the GPS it will automatically select the closest waypoint in the route as the “active to” waypoint and will show you the direction and distance to this point as you move. As you pass each waypoint in the route, the receiver will sequence and select the next waypoint as the new “active to” waypoint.

Track / Tracklog
A track is the direction of movement relative to a ground position. A tracklog is the collection of track points along the course of a route. It is essentially a “breadcrumb trail” of the path of the route to be navigated: tracklogs can tell us where we have been and therefore how to get back to where we started. There are limits on how many track points can exist in a tracklog file but modern GPS (like the Garmin eTrex Vista) can store 10000 or more tracklog points.

Tracklogs can be viewed on the map screen of your GPS and they can be activated just like a route. But contrary to a route, which shows you the straight line between two adjacent waypoints, the tracklog shows you the actual way you took. Many of the modern GPS-devices allow you to save tracklogs, albeit with a reduced number of track points. Note that a saved tracklog cannot be edited on the GPS but it can be downloaded to a computer and edited there. There are many third party programs available that permit downloading a tracklog. You can also reload edited tracklogs back into your GPS unit.

Of Headings, Bearings, Courses etc.

Following example will help you understand the confusing navigation terms.

Explanation of Course, Heading and Bearing

Course

Course or Desired Track (DTK): the compass course between the "from" and "to" waypoints. In the above example this would be 56°. The course does not change when you move unless you enter a new start or end point.

Heading

The direction in which you are moving with respect to true north, measured in degrees. 0° is North, 90° East, 180° South and 270° West. In the example above this would be 34°. In aviation and shipping Track is used to indicate the current direction of travel relative to a ground position whereas Heading provides navigational guidance only as it may differ from actual course due to winds, sea conditions, etc.

Bearing

In a GPS receiver, bearing refers to the direction (in degrees) from your position to your waypoint. In the above example this would be 56°. In other words: bearing is the direction you should be heading. If you are heading the right way your bearing, course and heading should be identical.

Crosstrack Error (XTE/XTK)

The distance you are off the desired course in either direction. In the above example this would be 22° to the left (to port). "To Course" gives you the compass direction required in order to return to original course. In the above example this would be south-east.

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