Does the iPhone get the GPS signal from my inReach?

Hello everyone,

I pretty much drawn my conclusion but I would like to hear from you.

As a local OSM contributor I use to hike with both my Fenix 6s Pro and my iPhone XS running Outdooractive to record the track, merge the two GPX files and use it as a guide for map editing.

Last week I've bought an inReach Mini, so I managed to merge not 2 but 3 tracks from the three devices.
What I've found is that inReach Mini and Outdooractive are pretty much identical, with only two minor differences:

sometimes very little slow movements (at the end of a path) are not drawn on Outdooractive maps, as if it enable GPS based on a fixed accelerometer threshold
twice during the hike Outdooractive didn't record the real track, but instead it recorded straight lines from point A and point B, not related to cellular data coverage as it worked elsewhere where I had no signal

Next time I'll disable Bluetooth on the inReach to force the iPhone to use its internal antenna.

So, my conclusion is that, as reported on some thread on Apple forums from many years ago, once paired to an external GPS receiver, the iPhone relies on that for the GPS signal, bypassing internal one.

Do you think the same?

0 twolpert over 3 years ago

Not entirely. Unlike Android, paired GPS units present themselves to iOS applications by way of location services. This makes it possible for iOS apps to use the external GPS with no extra programming in the app. Whether or not they actually DO SO depends on the level of accuracy requested by the app and iOS best guess as to the accuracy of the external GPS. vs. its internal resources (WiFi location, cell tower triangulation, internal GPS receiver). AFAIK, the app cannot request the use of a specific device. It's all based on the required accuracy. At least, that's the way I understood it the last time I looked into it, which has been a while.

Failure to use the GPS at low speeds is characteristic of some applications. App wants to know direction of travel. At low speeds, the implicit error in the GPS fix may may be larger than the true delta in position between fixes. In this situation, the direction of travel based on successive fixes is basically garbage. So the app just cuts off the use of GPS at low apparent speeds.

You will sometimes see similar behavior on the GPSr itself (not on the Mini) if it has a 2-D or 3-D compass. Above a certain threshold speed, it will use the GPS for heading. Below that threshold, it falls back to its internal compass.

0 Labronico over 3 years ago in reply to twolpert

In this case I may also throw in another test: another iPhone app which I used to use (ViewRanger) when paired to the inReach. I bet the inReach is treated by iOS as high accuracy GPS source, so if an app asks for that, that's were data will come from.

Thank you for the prompt response.

0 Labronico over 3 years ago

Did a quick test around home leaving the iPhone not associated to the inReach Mini.

I'd rate the quality of the tracks as follows: inReach > iPhone (Outdooractive) >> Fenix 6s Pro

Now the track for the iPhone is completely separated from the inReach one. Definitely Outdooractive (or maybe any app which requires a precise GPS) uses the inReach antenna when associated via bluetooth.

0 SpikySimonW over 3 years ago in reply to twolpert

twolpert said:
Unlike Android, paired GPS units present themselves to iOS applications by way of location services. This makes it possible for iOS apps to use the external GPS with no extra programming in the app.

Well I've certainly learnt something today - I had no idea this was the case - I didn't even know a device such as the iR Mini presented itself as an external GPS, I just thought it was A.N. Other bluetooth devices that transferred data to its own app!

Good to know.

0 4026301 over 2 years ago in reply to twolpert

Are there any new thoughts or learnings on this topic?