iOS6 Mobile Safari: Accuracy and update periods of geolocation.watchPosition

3 min read Original article ↗

I'm facing a strange behavior on mobile Safari on iPhone4 and iPhone5 on iOS6.

What I want to do

Tracking the user's location in the browser with high accuracy, using

geolocation.watchPosition({ enableHighAccuracy: true, maximumAge: 0, callback })

Problem I'm facing

Normally, when the device is outside, under clear sky and moving, the accuracy und the update period of the GPS positions is very good.

The coords object passed to the callback has an accuracy of 5 meters, a correct heading value is given and when moving the callback gets fired at least every 500ms.

But: Sometimes the watched position never gets accurate, even though I test it under the same conditions (as far as possible).

Also, the update period is much longer, almost 30 seconds.

Basically, in this cases, the HTML geolocation is not useable for the accurate tracking of a position.

Observations

  • This seems to happen, when the GPS-Sensor is not on "Hot-Standby", I mean it was not used for some time (not sure how long) by another native app.

  • Reloading the page, re-allowing the GPS access and re-initializing the watchPosition does not change anything, still bad accuracy and slow updates.

  • Changing the options passed to watchPosition does not seem to do anything.

  • Manual fix 1:

    • Close Safari
    • Open another native app like Maps or GMaps
    • Determine the position in the native app
    • Open Safari
    • GPS position is immediately accurate, following position updates are fired again in 500ms periods and are very accurate as well (no reload needed).

  • Manual fix 2:

    • Close Safari
    • Open settings panel
    • Disable Wi-Fi
    • Open Safari
    • Again, problem fixed (without a reload)

Conclusion

When the problem occured, I looked into the coords object of the callback and detected the following:

Even though the passed location is far away from the real position of the device (> 1km), the accuracy passed is much smaller (very often at 165 meters). The heading is never given.

When WiFi on iPhone is disabled, there is a hint in the settings panel that says enabling WiFi will enhance the accuracy of determining your location (because of AGPS which is supported by a datase of geocoded WiFi networks). But as far as I can see this is not true if you want to use GPS in mobile safari. In fact, it does the opposite.

It seems to me that mobile safari does something like this to determine the location:

  • If GPS is already activated/in use on the device, it uses the GPS sensor (fast and accurate position updates)

  • If GPS wasn't active before and WiFi is enabled, the device only uses its WiFi database to get the location. (very slow updates, not accurate). It just updates from one WiFi location to another. You can see this very clearly e.g. if you drive on federal roads, as your location mostly get mapped to the next residential area.

  • Only if GPS wasn't active before and WiFi is disabled mobile safari will use the GPS to determine the location of the device (again, fast and accurate).

Question

Can anybody confirm my problem and my observations? I worked with the geolocation in earlier iOS versions but never faced this problem before.

Is it a known bug for mobile safari, any chance that this will be fixed? Or am I just missing a better configuration of the watchPosition to get better results?