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What is an Electronic Compass?

Feb
29
2008

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.

11 Responses


  1. I actually HAVE an auto compas on the built in GPS in my Toyota Prius. It is very good and very accurate and kind of worthless. The only advantage I can see is to get started on the right foot. For example, when I program a route to somewhere on my TomTom from my home, it will invariable show the wrong way to head out and immediately go around the block. Most people can see this and make the necessary correction and the GPS will quickly catch on. The same sort of problem might occur if you stop for gas and wonder which way to go. It shouldn’t take a GPS to get you going in the right direction but if you do go the wrong way, it will help you correct your direction. However it may take you a long way around figuring there was some reason you left the interstate besides just stopping for gas.
    In short you still need to pay attention to where you are and where you came from and where you should be going.

    JeepLover - May 2nd, 2008
  2. I am interested in purchasing a large tract of land in a very mountainous area. I have a legal survey which shows azimuths which can be converted to compass headings. In order to find the actual survey stobs in the ground I need a GPS that will track my direction but also show me what direction to start walking, say for 315 degrees north. Any suggestions on what unit to look for that will do this?
    Thanks

    John - August 16th, 2009
    • John,
      I have a very similar need. I am into genealogy, and more and more cemetery locations are published with their GPS location. Additionally, I would like to determine the GPS location for some of those cemeteries the USGS doesn’t know about (old family plots, ‘lost’, etc.), others haven’t published, etc.

      Anyway, I want to get a device to do like you have noted. Have you had any luck?

      Martin - February 8th, 2010
  3. The electronic compass are, for the moment, just a gadget when considering cars. However, they are usefull in mobile robotics and any autonomous vehicles.

    The day when the cars will become automatic vehicle under control by a highway system, then compasses will be required. There is actual research in this domain in order to obtain fluid trafic and improved safety in heavily crowded highways around big cities.

    laurentien - November 11th, 2009
  4. I have a need for an electronic compass as I want to trek in places where there are sections of magnetic rock. A standard compass just spins. Mountaineering makes use of a number of devices to move safely, without a compass this can be very difficult in closed-in areas like forests or gorges or, of course, in bad weather.

    Andrew - December 30th, 2009
    • Obviously the “electronic compass relies on the same magnetic fields which make your “normal” compass spin, so it will be confused as well. The GPS section gives you the direction more reliably in magnetic rock – but you obviously would need to have an unobstructed “view” of the satellites …

      Klaus - October 19th, 2011
  5. I disagree with the uselessness of an e-compass completely! What if you want to stop and take a look at your on-board map and see the right ORIENTATION of the map in relation to which direction your “face” is facing” while standing still? There are plenty of uses. Compare what you’re doing with a GPS, to that of the activities you do when using a paper map. Picture it: You’re in the woods in Bear Mountain, NY, and you want to know what direction a planned waypoint is that’s 100 yds away, but only using our GPS. You can’t DO that with a gps without an Ecompass! Right? Because if you shut your ecompass off, you’ll notice that your onboard map will drift around like crazy, ratcheting in strange circles continuously. But my GPS doesn’t do that when I have my compass on. Some people report the opposite. But mine? Well, my GPS is an expensive high end one and it orients the map properly when you’re standing still. Thank God (actually, thank the Military). It’s a tool that I just can’t do without.

    Marsh

    Marshall - May 13th, 2010
    • In your example, I’d set the map to be “North up” instead of “heading up” in order to eliminate the drifting/circles issue you described.

      Tim - May 13th, 2010
  6. I own a heating oil company and operate 35 vehicles that make home deliveries. 50% of the time, when the vehicle departs, the GPS points in the wrong direction because the truck backs in most of the time. To add further insult, they are large trucks that can’t turn around easily. This issue has cauased untold loss of efficiency. I would kill for an automotive GPS with a built in Electronic compass. I would buy 30 of them tomorrow. I am told there is a Garmin with an electronic compass, but after talking to their tech support staff, they said it was NOT a compass. This is the model. https://buy.garmin.com/shop/shop.do?cID=134&pID=69452

    Anyone care to clarify this? Anyone used this GPS or know of any with a compass?

    Gary - January 30th, 2011
    • Yes, that model does have an electronic compass.

      Tim - February 7th, 2011
  7. I am the proud owner of a Garmin Oregon 450t with built in “electronic” compass. Now I wanted to demonstrate this gadget to another hiker, he wasn’t impressed – even less was I. I guess its my NiCad rechageable batteries which latch the compass in one direction because they could be ever so slightly magnetised :-(

    Klaus - October 19th, 2011



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