Six iPhones tested, and they can't agree on magnetic north

Another reason to keep your your phone in your pack.

Six iPhones tested, and they can't agree on magnetic north

Cell phones, iPhones and the like are fine to use as communication devices, but as compasses, GPS's and other so called "Out Door Apps" should be used with a giant grain of salt.

See you on the trail....Walker

Thanks for posting. It looks like they were only using the internal compass and not the phones GPS compass. Haven't checked out my phone's compass' directional accuracy yet. I've found my phone's GPS to be pretty accurate in the woods thus far - certainly beyond a novelty. The first couple of times I used it the GPS track was over reading my mileage - especially on the way up, so I lowered the sensitivity and it was pretty much spot on (carrying in my shorts' pocket).

FWIW I have an LG Intuition and I use the Trimble Outdoors 'Backpacker DPS Trails Lite' App

My iPhone 5 slightly overreads my bicycle commute (using the Strava app), as compared to both my Garmin 76CSx and my calibrated cyclo-computer. My minimum commute to work is 11.7 miles and it usually reads 11.8-12.0 (never comes in lower). Will compare it to the magnetic compass and GPS compass when I get a chance. If I go for a walk along the RR tracks to the adjoining office parks, and follow along with Google Earth, I am within 25' of the RR tracks in real time.

Tim

TJsName said:

I've found my phone's GPS to be pretty accurate in the woods thus far - certainly beyond a novelty.

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I have compared GPS tracks recorded by a friend's iPhone and my 60CSx. The iPhone track had a lot of large excursions from our route. The 60CSx track was significantly better.

This comparison was not fully controlled--we just compared tracks after the hike. My GPS was in the top of my pack but I don't recall how my friend carried his iPhone.

Doug

I just did a quick test using a map for the lines. The Sunuto compass set a mag north, the iPhone was 0 and the Garmin 76CSx said 353.

There could be device interference between the devices. The iPhone definitely moves the compass needle.




Tim

"GPS" is way different than "compass". Most of these phone gizmos seem to be moderately reasonable about telling you where you are, but unless you are moving fairly rapidly, I doubt a GPS-based device has much of a chance of pointing you in any particular direction.

I have that "show me hills" android app everyone raves about, and I've played around sitting at places I *know*, looking at peaks I am absolutely sure about. It gets my position to 50 feet or so (which for a GPS I consider crappy, my "real" GPS typically gets +/- 10 ft or less), but I've NEVER had it come anywhere close to get the direction right. We're talking 20 or 30 degrees off. Sometimes worse. If I depended on this POS for backcountry navigation, I'd be dead in a ditch somewhere. My GPS "compass" function is somewhat better, but no way would I use even that for shooting a bearing. Come on folks, a $20 piece of plastic Silva/Suunto can easily get within a degree, the hardest part is knowing your declination. But when magnetic is off by 20 degrees, declination correction is kinda irrelevant.

I used Guthook's app for navigation on the PCT and it was accurate every single time I checked it, which was often. It shows a trace over laid on a topo map and "you" are a small blue dot. There wasn't a single time that dot was not right on that trace while I was on the trail.

We got off the trail in the desert at night and it was as simple as "walk toward the trace" until the dot was shown on the trace and boom - the trail would be under your feet!

In fact there was one time that I thought that the app must not be finding my location correctly but it turned out that I had taken a wrong turn at a junction and was a few miles from my trail...

That being said, I certainly had a Suunto and paper maps but never needed them - I feel my phone did a perfectly fine job for my purposes.

The 76CSx doesn't use the GPS for the compass. From http://www8.garmin.com/products/gpsmap76csx/spec.html

Electronic Compass Feature (GPSMAP 76CSx only)

Accuracy: ±2 degrees with proper calibration (typical); ±5 degrees extreme northern and southern latitudes Resolution: 1 degree

My attempt was strict a back-of-the-envelope attempt - I didn't do multiple runs and isolate all the devices or anything.

Tim

bikehikeskifish said:

The 76CSx doesn't use the GPS for the compass. From http://www8.garmin.com/products/gpsmap76csx/spec.html

Electronic Compass Feature (GPSMAP 76CSx only)

Accuracy: ±2 degrees with proper calibration (typical); ±5 degrees extreme northern and southern latitudes Resolution: 1 degree

Click to expand...

Actually the 76CSx (and 60CSx) have two methods of generating a compass display:

1) GPSes without a magnetic sensor can determine the direction of movement from one's horizontal velocity vector. (The solution of the GPS equations yields a 3D velocity as well as a 3D position.) If the GPS is held in the "standard orientation", the displayed needle will point the same way that a mechanical magnetic compass will if one moves fast enough. No calibration is required. This method, of course, will not work for a stationary GPS.

2) GPSes with a magnetic sensor ("sensor" units in Garmin parlance) including the 76CSx, 60CSx, 62s, 78s, and others, can directly sense the magnetic field to produce a display similar to that of a mechanical magnetic compass (when properly calibrated) with or without motion. This is the only way for a GPS to determine direction when stationary--when moving above some threshold speed they switch (or can switch) to mode 1).

The currents within electronic devices produce magnetic fields and can alter the readings of nearby magnetic compasses (electronic or mechanical). (The devices may also contain magnetic materials or intentional magnets which will have the same effect.) Thus the unit should be kept well away from anything else that might affect it when in use. (This also applies to mechanical compasses...) Calibration measures the magnetic field produced by the device itself and removes its effect before displaying the direction. (Boat and aircraft compasses also need to be calibrated and compensated.)

There is a form of GPS compass that can determine direction without motion, but it is not practical for hikers as it requires two or more antennas separated by a significant distance.

Doug

Pretty sure my dining room table was not moving fast enough to switch the GPS out of magnetic mode

Tim

bikehikeskifish said:

Pretty sure my dining room table was not moving fast enough to switch the GPS out of magnetic mode

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Probably not unless you gunned the engine on the motorhome...

Doug

bikehikeskifish said:

Pretty sure my dining room table was not moving fast enough to switch the GPS out of magnetic mode

Tim

Click to expand...

It doesn't switch by itself. You have to manually put it in or out of magnetic compass mode. It's in the user's manual. If your gps happens to be in electronic gps compass mode, you will get random direction indications when it is not moving.

While the electronic gps compass works for its purpose as long as you are moving at a reasonable speed, I would never use a gps in magnetic compass mode for direction finding. That is what a real compass is for.

Page 30 of my manual described how to tell the 76 CSx how to switch based on speed. The online version is not copyable (PDF) so I can't easily paste the quote here, but you can go here and read for yourself:

http://www.vanderbilt.edu/ees/uploadfiles/GPSMAP76CSx_OwnersManual.pdf

Since my mobile home was parked in my driveway when I went out there to do the experiment, I'm pretty sure it was not moving. Although, I know that if I leave the GPS on and record a track, it will think it ran around in circles

The 76CSx and iPhone are sitting here watching the World Series, not moving, and the GPS has the magnetic compass icon indicating magnetic mode. They are within 2 degrees of agreement

Tim

Nessmuk said:

It doesn't switch by itself. You have to manually put it in or out of magnetic compass mode. It's in the user's manual. If your gps happens to be in electronic gps compass mode, you will get random direction indications when it is not moving.

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My 60CSx (running software ver 4.00) can certainly switch compass modes by itself. You can set speed and duration thresholds:
main menu> setup > heading
The lower half of the display has the fields:
Switch to compass heading when below:
0 m h
for more than...
90 sec
(these are my settings. "m h" means mph)

The 62s is similar except the (magnetic) compass settings are "auto" and "off" with no way to set the thresholds.

Note: the 60CSx and 76CSx are electrically identical and the 62s and 78s are also essentially identical.

BTW, the Garmin manuals are incomplete. I generally read the manual and then play with the GPS (including traversing the entire menu system) to determine the features of the unit.

Manuals direct from Garmin:
60CSx (Aug 2007):
http://static.garmincdn.com/pumac/GPSMAP60CSx_OwnersManual.pdf
76CSx (May 2009, the one in Tim's link is dated Aug 2007).
http://static.garmincdn.com/pumac/GPSMAP76CSx_OwnersManual.pdf
62s (Aug 2011):
http://static.garmincdn.com/pumac/GPSMAP62_OM_EN.pdf

To find the manuals for Garmin GPSes, look up the model info on http://www.garmin.com and click on manuals. These are often more up-to-date than the paper manual in the box.

Doug

My mistake, I read the manual where you turn on/of mag mode (on page 30) but forgot about the next paragraph where you could set the switch-over speed. I have two 60Csx units and a 62s, but never use the magnetic compass setting. One time I must have mistakenly sent it into mag mode and it took me a while to figure out why it was acting so screwy. I am never without a traditional compass. My gps is used for canoe racing and training, mainly just for maintaining target paddling speed when in areas that I have some familiarity. In the 1000 mile Yukon races they are indispensable for being competitive because of the broad expanses of water and traversing the preplanned correct side of thousands of islands and shoals. For remote backcountry recreational hiking off trail, I am strictly passionate about traditional map and compass and don't have any need to rely on or use gps. But for my duties in SAR, the gps is an absolutely necessary addition (along with a real compass).

Is the efficiency compromised when...

I'm ignorant when it comes to the new iPhones, smart phones, etc, so this question might be easy to answer (maybe not). With these phones, when you move out of cell tower range, is the efficiency compromised?

See you on the trail...(using my Garmin 60CSx, compass, & map).....Walker

walker said:

I'm ignorant when it comes to the new iPhones, smart phones, etc, so this question might be easy to answer (maybe not). With these phones, when you move out of cell tower range, is the efficiency compromised?

See you on the trail...(using my Garmin 60CSx, compass, & map).....Walker

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Many (most?) of the smartphones now being sold have the GPS function built-in and 'listen' for satellites in much the same manner as a dedicated GPS. Whether or not the smartphone is within range of a cell tower has no bearing on that function.

Kevin Rooney said:

Many (most?) of the smartphones now being sold have the GPS function built-in and 'listen' for satellites in much the same manner as a dedicated GPS. Whether or not the smartphone is within range of a cell tower has no bearing on that function.

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Many of the older smartphones used a protocol called AGPS (Assisted GPS) which used info from the cellphone system to help acquire the satellites. I believe that some even sent the raw (pseudorange) data back to a computer via the cellphone system to compute the location. Fortunately more recent smartphones seem to be getting away from this dependance.

However, the speed of satellite acquisition and ability to maintain lock in poor conditions may or may not match that of modern dedicated GPSes (eg 60CSx, 76CSx, 62s, and 78s).

The 60CSx can find 4 or more satellites in a few seconds and a lock in 30-45 seconds (the 30 second delay is the time to download orbital data from the satellites) from a cold start and only a few seconds for a warm start (it already has current data). It can also maintain lock in the tree cover and valleys typically found in the Whites. A smartphone may or may not perform up to these standards depending on the details of its design and implementation.

Doug

My GPSr points to True north while my compass points to magnetic. I don't have an iPhone but could the ~15 degree discrepancy they are seeing be as simple as the iPhone is calibrated to true north?

HockeyPuck said:

My GPSr points to True north while my compass points to magnetic. I don't have an iPhone but could the ~15 degree discrepancy they are seeing be as simple as the iPhone is calibrated to true north?

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The algorithm to calibrate the compass looks for maximum/minimum magnetic field strength, so without a working GPS magnetic north will be displayed.

However, if the compass knows where it is, software could add the necessary correction. I feel that a good user interface would inform the user if corrections are being applied....but you dont find that on Iphones or GPS's