What is an Electronic Compass?

A question we get time and time again is “what is an electronic compass?” After-all, GPS devices are electronic and they can tell what direction I’m going. So shouldn’t all GPS devices be known as having an electronic compass? Well, not quite. Here is what you need to know about how GPS devices deal with headings, direction, and compass readings.

GPS by itself is a fairly limited technology. All it does is allow a device to determine where it is… nothing else. It is what GPS devices do with that location information that makes them tick. The GPS system itself can only provide information about where the device is. At the core GPS does not provide speed information and it does not provide direction information.

However, both direction and speed can be derived if you know some history about where the device has been. If you have a GPS reading from two locations, you can draw a straight line between those two points and determine the average direction. If you have a GPS reading from two locations and the time from each reading you can determine the average direction and the average speed between those two readings.

Movement is Necessary

Note that in order to determine direction, you need to be moving While standing still the GPS cannot determine what direction you are facing. Let’s say you live on a long private driveway that runs North/South; your home is at the North End and the road you live on is a the South end of your driveway. You drive from your home to the end of the driveway. The GPS will recognize that at one moment you were at the North end of the driveway and a few seconds later you were further South, so it will assume you are moving South and will show you driving in that direction.

Now suppose you have reached the end of your driveway at the road. Instead of turning around, you put the car into reverse and drive backwards up the driveway. The GPS will think (somewhat incorrectly) that you have turned the car around and are driving forwards back towards the house. With most GPS devices in a “heading up” setting it will not keep the direction you are facing up since it doesn’t know what direction you are facing. It will put North up in this case because that is the direction you are generally moving and it assumes you are facing in the same direction you are moving. In fact, the GPS will show the exact same thing if you drive backwards up the driveway as it would if you turned the car around and drove forwards up the driveway.

Auto GPS

In most cases, especially as it pertains to auto GPS devices, this isn’t a big issue. The car is generally facing in the same direction it is moving. At lest you hope so! However things get a little more interesting as it pertains to outdoor/recreational GPS devices.

Recreational GPS

Think of yourself walking along a trail in the woods. You want to know what direction you are walking. So you stop and pull out your GPS. Since you are stopped, your GPS doesn’t know what direction you are facing! Remember, it can only figure out direction if there is movement. However a GPS will commonly show on a compass the last known direction. But, if you are looking at the compass on your handheld GPS and turn around in place, the GPS will not be able to sense you have turned around.

Also keep in mind that GPS devices tend to be accurate within about 10 meters. Imagine a worst case scenario where one second your GPS thinks you are in one place, and the next second it thinks you are 30 feet away. That apparent movement (from the perspective of the GPS) could be enough to fool it into thinking that you are moving in a direction you really are not moving. In practice this doesn’t happen too often, but a good rule of thumb is that to determine direction, walk with you GPS in a straight line at at least about 2mph, for about 30 feet in order for it to show you a good direction.

Can we get back to the Electronic Compass?

Yes, so here is where an electronic compass comes into play. An electronic compass doesn’t rely on GPS signals to determine direction. As such, it doesn’t rely on movement to know your direction. Therefore if you turn around in place with the GPS, the compass should continue to point in the correct direction.

Sounds great, right? Well, in some cases it is. But there are a couple of drawbacks to be aware of. Electronic compasses require additional hardware to be crammed inside the GPS; this leads to higher costs as well as somewhat shorter battery life.

So should I get a GPS with it?

For auto GPS devices there is hardly a choice. Almost none of them have an electronic compass which is fine since you don’t really need one. Your GPS can still likely display a compass on the map screen and the device will know what direction you are going because you are typically moving.

For outdoor/recreational users you will need to make a decision how much of an inconvenience not having the feature is. You can always determine/confirm direction by comparing a tracklog to the map, or by walking a short distance and watching the compass. In most environments when you are using a GPS outdoors you probably want to have a physical separate non-battery operated compass with you anyway, so many people have no need for an electronic compass. However if you can spare a little bit of battery life and want to spin around in circles in place and have the GPS still know which way is up, the feature might be worth it. For me personally, I can do just fine without it and don’t feel directionally challenged as a result.

Located in GPS, GPS 101, GPS Definitions on Feb 29, 2008