GPS issues

Your GPS location might not be available, or might be slow to obtain, for a number of reasons. These can be related to your phone’s general settings, settings on the app, or to environmental or hardware factors.

You might also observe trip recordings that don’t appear to show your true progress, only recording periodic points that show up as a series of jagged lines, or sometime adding points even when you are standing still.

Check through all the following options to see what might be the issue, and for tips on obtaining good location accuracy.

GPS settings on the app

To display your GPS location on the chart you will need to turn on GPS positioning in the app – simply tap the satellite icon at the bottom left of the screen. GPS positioning will also turn on if you start recording a track.

To see your GPS location you will need to allow the app to have access to your location. When you first activate GPS positioning you will get a prompt to give this permission. Depending on your operating system you may have several options including to allow the access, allow it only once, or to deny permission.

To check your current permission settings you can either use your phones ‘Settings’ app, or check on the settings page in the app itself. Look under the controls section for ‘location status’.

It is also worth noting that some devices do not actually have a GPS chip in them and cannot measure your GPS location. This may not be immediately obvious as the device can still estimate its location in urban areas using cellular and wifi signals, but you will not be able to determine your location as soon as you are off-line or outside of cellular range. It is however possible to use external plug in GPS devices with most phones/tablets if you really need GPS measurements.

Accuracy filter. On the settings page of the app there is an option for filtering our inaccurate signals in a track recording. This can be useful to avoid poor quality signals being including in the recorded track, but can also result in very few points being recorded if signal accuracy is low and the filter setting is set too low. If you find that your trip recordings show jagged lines with most of the track details missing then check that this filter setting is not set too low.

System settings

(1) Master Location Access. It is possible for you to turn off access to your location in a number of ways which will result in the NZ Charts app (and all other apps) not being able to determine your position at all.

On an iPhone you can do this from the Settings App, under Privacy, Location Services. Toggle the switch to turn on/off location access on your phone. Further down the same page you can also check and adjust the individual access permissions for all of your installed apps. For This is done Main on/off location settings. For proper functioning of the app make sure that Location Services is on, and that the app settings displays ‘While Using’ (or ‘Always’).

Environmental factors

GPS signals are relatively weak signals and can be distorted or blocked by overhead or surrounding objects, or even by adverse weather conditions. This can affect both accuracy and availability. GPS satellites are also non-uniformly distributed in the sky and at different times the combination of available satellites may give an inferior signal (particularly in NZ which is of lower interest for satellite coverage and satellites tend to be concentrated lower on the horizon rather than overhead). For best location accuracy try to avoid heavy overhead cover or objects that block line of sight to the sky and horizon, avoid use of thick or metallic phone covers, and avoid burying your phone deep under other equipment.

Sometimes you may observe that it takes a long time to obtain an initial GPS location (or GPS ‘lock’), particularly when out of cell phone range or with wifi turned off (eg in flight mode). This is normal but can be exacerbated by poor signal conditions or by not having a recent approximate location reading. Once a ‘lock’ is obtained then measurements should be accurate and rapid as long as good signal conditions are maintained. If you wish to record a track and have an accurate start time or position then it is a good idea to switch on GPS in the app in advance to give your device time to obtain a GPS lock.

Trouble Shooting

Try toggling Location access on and off again (see above under System Settings)

Try restarting your phone (power off, on again)

Find an open spot with clear access to the sky and wait 10-15 minutes to see if an accurate GPS location is obtained.

Check other location apps to see if there is a difference in behaviour.