GPS altitude readings are badly wrong on Samsung Galaxy S23 Ultra

[OS]

Last Monday, I took a flight from London Stansted to Belfast International Airport and decided to record the track (in Airplane Mode). GPS connection was fine, and my horizontal position was displayed correctly, but soon after takeoff, I noticed that the displayed altitude of about 400m seemed to be too low for the view from the window. So, I opened a GPS Test app, which showed an altitude of over 4km. After about 20 minutes, the altitude on Locus Map reached the correct value in a nonuniform and inconsistent fashion (going up and down tens if not hundreds of meters for no reason while GPS Test displayed sensible and consistent values). The same happened on the descent with the altitude reading of 1765m at Belfast International Airport's runway (while 136m in GPS Test). I also compared the GPS Test's altitude readings with that of the Garmin's Earthmate app, and they were consistent.
Note that the activity type was set to walking, but I tried different filtering modes and then disabled filtering completely. This didn't help. I made sure these were actual GPS-based (not barometric) readings.
Attached (in multiple forum entries due to the attachment size limitations) are the screenshots from my phone showing Locus Map alongside other apps displaying the altitude. Note that for some reason, GPS Test reports a higher number of used satellites than Locus Map. The recorded track split into two .gpx files (because I restarted the recording trying to fix the issue) is also attached.
Let me know if you need more information.

[OS]

another attachment

[OS]

further attachment

[OS]

final attachment

[Menion]

Hello OS,
thanks for the huge amount of screenshots  . I was mainly curious about your setup in the Altitude manager screen, where seems to be everything "correctly" disabled. In such case, the received altitude should be completely un-affected by any internal optimization and visible values should really be values that Locus Map received.

The question here is what values the app receives. In the app settings > GPS & sensors is a setting called "Google Services assisted location". This switch between two modes. First (when disabled) is the old method where the app receives raw data. The second use pre-computed values by the Google Play services library and I've already noticed that in rare cases, values were not correct. So if you have an option to test it, suggest disabling this setting and giving a second try.

[OS]

Hi Menion,
Thank you very much for your suggestion.

Disabling "Google Services assisted location" solved the problem.

I've tested it on two more flights, and the unfiltered altitude readings usually match that of the "GPS test" app within one meter. The filtered readings have delays, but this is expected as the activity type was set to walking.

[Andrew Heard]

menion, what is the supposed advantage of Google Services here?

[Menion]

Hello Andrew,
I've asked ChatGPT and here is quite nice answer:

Comparing Google Location Services API (part of Google Play Services) with the older method of accessing device location without Google Play Services involves looking at several factors from a user's perspective. Here's an overview:

### Google Location Services API

**Advantages:**
1. **Improved Accuracy:** Google Location Services combines GPS, Wi-Fi, cellular networks, and other sensors to provide more accurate and faster location fixes.
2. **Battery Efficiency:** It's more battery-efficient, especially with features like the Fused Location Provider, which smartly switches between different location methods.
3. **Ease of Use:** Offers a more user-friendly experience with higher-level APIs and better integration with other Google services.
4. **Geofencing and Activity Recognition:** Additional features like geofencing and user activity recognition are useful for advanced location-based services.
5. **Regular Updates:** As part of Google Play Services, it receives regular updates independently of the operating system, ensuring access to the latest features and improvements.

**Disadvantages:**
1. **Dependence on Google Play Services:** Not all devices (especially in certain regions like China or on some custom ROMs) have Google Play Services installed.
2. **Privacy Concerns:** Some users might be wary of sharing location data with Google due to privacy concerns.
3. **Potentially Intrusive:** Google Location Services can be seen as more intrusive, as it often provides more detailed location data.

### Older Method (Without Google Play Services)

**Advantages:**
1. **No Google Play Services Required:** Works on all Android devices regardless of Google Play Services availability.
2. **More Privacy-Controlled:** Users who are concerned about sharing data with Google might prefer this method.
3. **Direct Hardware Access:** Can offer more control over specific hardware components, like GPS.

**Disadvantages:**
1. **Less Accurate:** GPS alone without assistance from networks might be less accurate, especially in urban or indoor settings.
2. **Slower to Get First Fix:** It might take longer to get the initial location fix using only GPS.
3. **More Battery Consuming:** Typically consumes more battery as it lacks the optimization present in Google's Fused Location Provider.
4. **Complexity in Development:** Developers need to handle more scenarios manually, like choosing the best location provider, which can lead to more complex code.

In summary, Google Location Services provides a more advanced, accurate, and battery-efficient way of handling location but requires Google Play Services and involves sharing data with Google. The older method offers more privacy and independence from Google Play Services but at the cost of accuracy, battery efficiency, and increased development complexity. The choice between the two methods depends on the specific needs and constraints of the users and the application.

I'm surprised by the "Privacy Concerns: Some users might be wary of sharing location data with Google due to privacy concerns.", because I see no reason, why location data needs to be shared out of the device and I've also never read about it ... interesting.