What's with the arrowhead on Google Maps "location" symbol?

[jc1742]

Google maps on my android gadget (HTC ONE) shows a little blue circle for "you are here", and it has a little arrowhead pointing off in what seems a random direction. I've been trying to discover what it means, and/or how to make it useful, but haven't succeeded.

The weirdest part, which disproves most hypotheses, is that when I hold the phone level and rotate it, the arrowhead rotates around the circle at twice the speed as the phone rotates. Right now, sitting in a chair facing south, the arrow points SE (on the map). If I rotate the phone 45º clockwise, the arrowhead moves 90º to point SW on the map. Another 45º rotation makes it point NW, a 3rd makes it point NE. A 4th rotation gets it pointing SE again, but the phone is now 180º from where it started.

This behaviour proves that the arrowhead's direction isn't any (useful) sort of "compass". The fact that its initial direction is essentially random when google maps is opened emphasizes this. Walking the phone around causes the blue dot to move around on the map, but the arrowhead's direction doesn't change, so it has no relation to the phones physical motion across the landscape.

I've seen map apps where such an arrowhead indicates the phone's motion (in space, not rotation), and this would be useful. Someone went to the the trouble to implement the arrowhead in the google maps app, but its behavior doesn't seem to correlate with anything I do with the phone.

Is this just a bug? Or is it doing something useful that I haven't been able to guess? Is there a way to make it say "I'm moving in this direction"?

Yes, I did google the issue, and searched for it in androidcentral, but I apparently haven't guessed the right keywords, because all the hits talk about things that are unrelated to this mysterious little symbol. I did stumble across the suggestion to do a figure-8 motion to calibrate something, but it had no effect on this behavior, though perhaps I didn't do it right.

 

[puch96]

I think that there is a bug with the way the arrow displays.
It is meant to show you the direction of travel if you are in 2D mode, but lately the arrow does not correspond to the direction of travel correctly.

 

[SpookDroid]

Hi there,

The 'arrowhead' is not a compass per se, although it is called 'compass mode'. It's meant for the map to face whatever direction you're facing.
https://support.google.com/gmm/answer/2839801?hl=en&ref_topic=3137761

 

[Rukbat]

The arrow points in the direction the phone moved (horizontally, from one place to another) between the last reading and the current one. If you're in the same position (and rotating in a chair won't change your position by more than a few inches if the phone isn't sitting exactly over the rotation point of the chair - if it is, its position isn't changing), the "direction" is determined by the changes in timing of the signals - the inherent error in GPS. The arrow isn't pointing in the direction you're going relative to the phone, it's pointing in the direction you're going relative to the map on the screen.

Sit in a moving car and watch the arrow and it'll point in the direction you're going. Stop at a light and it might show you turning to and fro or even in a circle - but at the same location (+/- a few meters).

Install GPS Status & Toolbox and watch the DOP (Dilution of Precision) figure - that's the accuracy of your location - and you'll notice that with the phone sitting still on a table it constantly varies (by just a little, but enough to make your "direction" change).

If you search how gps works you'll find articles that go into this in more detail, and you'll understand why a GPS itself (without the help of other [earth-based] signals can't be completely accurate - like within an inch. You'd need a nearby ground station transmitting its known location and the location GPS is reporting it to be at [and a receiver to receive its signal], so your GPS receiver would know the current [this second kind of "current"] GPS error). There are millimeter GPS systems - they're accurate to within a millimeter or two - but the price is more like that of an expensive car than an expensive phone.

 

[SpookDroid]

Also remember that if you're only looking at the map, the location polling is not 'real time' (as in 'not constantly polling') to conserve battery. Only if you're in an active navigation route will the app constantly poll for your current location.

This, and Rukbat's very accurate (and very awesome) explanation should account for the direction variations you're seeing when moving on a chair.

 

[jc1742]

The arrow points in the direction the phone moved (horizontally, from one place to another) between the last reading and the current one. ... Sit in a moving car and watch the arrow and it'll point in the direction you're going. Stop at a light and it might show you turning to and fro or even in a circle - but at the same location (+/- a few meters). ...

Nah; it doesn't do that. A couple of days ago, I was the "navigator" in our car while my wife drove. For several hours, we were mostly driving NE or E, and the little arrowhead on my HTC ONE almost always pointed backward to the direction we were going. It showed us moving along the road quite accurately, including showing us passing crossroads as we actually crossed them. But the arrow's direction ranged from W to SE, never within 90º of our actual travel direction as shown accurately by the blue dot's position on the map.

My main theory is that the arrowhead is simply "broken". Whatever it's doing has nothing to do with how the phone is moving. Weirdly though, it does respond consistently to rotating the phone, so it's measuring something. It's not acting like any sort of compass, though, since its direction varies in a nonsensical fashion.

I am familiar with the accuracy problems of GPS, but that doesn't seem to help in this case. If it were the problem, how could google maps be accurately showing our position on the map, to within a few meters, as we drive along a road? It doesn't show our location moving backwards or off the road (except when we do drive off the road, as into a driveway or parking lot), but the arrowhead points those directions most of the time.

So for now, I'm going with "broken". ;-)

 

[jc1742]

I think that there is a bug with the way the arrow displays.
It is meant to show you the direction of travel if you are in 2D mode, but lately the arrow does not correspond to the direction of travel correctly.

I think we have a winner! As I remarked in an earlier message, the top hypothesis on my list is "broken". I thought that it was for showing direction of travel, probably because on my old HTC G1 (R.I.P.;-), that's what it did. But on this HTC ONE (or perhaps on recent "upgrades" of google maps), it clearly doesn't do that. The fact that it responds consistently (if weirdly) to rotating the phone shows that the code is doing something consistently with the arrowhead, but whatever it is, it has no correlation with direction of travel. Well, a small correlation: It's usually more than 90º off the direction of travel. If it were random, it'd be within 90º half the time. So it's not random, and has a small negative correlation with direction of travel. But I don't know what it's measuring.

 

[BargainingJew]

The arrow points in the direction the phone moved (horizontally, from one place to another) between the last reading and the current one. If you're in the same position (and rotating in a chair won't change your position by more than a few inches if the phone isn't sitting exactly over the rotation point of the chair - if it is, its position isn't changing), the "direction" is determined by the changes in timing of the signals - the inherent error in GPS. The arrow isn't pointing in the direction you're going relative to the phone, it's pointing in the direction you're going relative to the map on the screen.

Sit in a moving car and watch the arrow and it'll point in the direction you're going. Stop at a light and it might show you turning to and fro or even in a circle - but at the same location (+/- a few meters).

Install GPS Status & Toolbox and watch the DOP (Dilution of Precision) figure - that's the accuracy of your location - and you'll notice that with the phone sitting still on a table it constantly varies (by just a little, but enough to make your "direction" change).

If you search how gps works you'll find articles that go into this in more detail, and you'll understand why a GPS itself (without the help of other [earth-based] signals can't be completely accurate - like within an inch. You'd need a nearby ground station transmitting its known location and the location GPS is reporting it to be at [and a receiver to receive its signal], so your GPS receiver would know the current [this second kind of "current"] GPS error). There are millimeter GPS systems - they're accurate to within a millimeter or two - but the price is more like that of an expensive car than an expensive phone.

This is completely inaccurate, on every level.

Posted via the Android Central App

 

[Sebastian Gardner]

I'm relieved to know I'm not the only one who has spent futile time trying to decipher the meaning of the arrowhead. In fact with my Galaxy Note I find that the Google map correlates in no intelligible way with the orientation of the phone. If I point the phone in a different direction, the map changes, but completely arbitrarily. This makes the whole thing as good as useless when, say, you're on foot in a city and trying to work out, at a junction, which of the several roads is the one you want. Or is there some trick I've missed?

 

[swamp thing]

The blue arrowhead that swivels around the blue dot, tells you which way the phone's body is pointing, assuming that you are holding it with the screen horizontal. In portrait mode, that corresponds to a line running straight out from the top edge of the screen and parallel to the ground. This feature is available only in devices that have a compass sensor.

In other words, the blue arrowhead symbolizes a tiny phone drawn on the map's surface, oriented on the map in the same way that the real phone is oriented on the earth's surface.

If you want to confirm this statement, try this experiment for yourself (hold the device with the screen horizontal during this test). This experiment does not require that your compass be very accurate, only that it should be able to detect rotation reasonably well.

[1] Tap once or twice on the blue target (or compass icon) (near bottom right of map screen). The icon will toggle between a blue target like this : .... and a blue compass like this .... . This lets you select two corresponding modes of operation.

[2] Select the "blue compass" mode as explained in step 1. In this mode, the red-and-grey compass near the top left of the screen will be enabled and will point towards magnetic north as found by your compass sensor.

[3] Rotate the phone slowly in a horizontal plane while watching the blue arrowhead (center of screen.. ). You will see that the arrowhead ALWAYS points to the TOP of the screen. The map itself swings around so that it's "north" is always aligned towards a certain physical direction. (That direction should be true north if your compass is any good, but that is not very important here). So if the device is held pointing east, then the arrowhead points to the map's "east" edge.

This observation may seem rather trivial or obvious, but it helps make sense of what comes next...

[4] Hold the device so that the TOP edge of the device's screen is PARALLEL to the red-and-grey compass. In other words, the phone's body is held horizontally and pointing EAST, based on the google map compass. (We don't care whether the compass is right or wrong). The whole thing should look like this:


[5] Now tap the blue compass icon so that it changes to blue target mode. The red-grey compass changes briefly into a map-style compass rose (Red arrowhead with an "N" below it), then it just disappears.

[6] See how the map swings through 90 degrees so that its north edge matches the top of the screen (which is the meaning and purpose of the "blue target" mode.

[7] Your phone is still pointing east (it really should, because did not move it while tapping the blue icon). But -- here's the important thing --the little arrow now points to the RIGHT edge of the screen, which is the map's EAST !!

Here is how it should look:



If you turn the device 45 degrees to point southeast then the little arrow will also swing to southeast on the map.

[8] Repeat steps 4 to 7 with any other orientation of the device, and you will soon be convinced that this, indeed, is what the arrow is all about.


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[TimothyNathan]

Thank you for that excellent and accurate description of how the arrowhead displays, which I have validated.

My question is (and maybe I am being dim) does it serve any useful or practical purpose?

 

[swamp thing]

Hi Timothy,

Assume that from where you stand, you can see five or six mountains in different directions (or there are 5 roads leading away from that spot). All the mountains look the same, and you have no other clue.

You want to know : "which one of those peaks is Mt. Timothy?" All the peaks are labeled on your Google map - and one of them is labeled Mt. Timothy.

What you now do is slowly turn the phone until the blue arrowhead points to Mt Timothy on the map. Now just walk in the direction that the top of your phone is pointing, and you will be walking towards Mt. Timothy.

-- This is valid in either of the two modes that I described in my earlier post. Only, in one mode the map will be "stuck" on you screen, while in the other mode the map will swivel around to stay aligned with the "real" landscape. --

Edit : This might be even handier in thick fog when you can't even see those mountains. A bit less confusing than mentally referring to the compass north, comparing it with Mt. Timothy's bearing from you (on the map), and figuring out which way to walk. But in the other mode (where the map aligns with the landscape), the arrow is less useful -- I guess it stays on just for consistency.

Regards,
s. t.

 

[TimothyNathan]

Thank you, all very clear.

Does my mountain have a huge carving of me in living rock?

 

[swamp thing]

Use your map to go there and find out !