Great question — answering as the UphillTech team:
it turns out the raw GPS-data is not on the phone itself but in the modem! (... or may be even more difficult to grab: it is in the Network!) Modems are usually full GNU/Linux-systems with closed firmware. Even though this closeness violates the GPL, it has been proven to be very difficult to have access to the source code of a modem-firmware. One fo the few positive examples is the story behind the Pinephone's modem manufactured by Pine64. Behind the scenes there is 3GPP-Consortium. Some of it members are Google and Qualcomm. it is possible to extract GPS information if you manage to talk to the modem. Sometimes serial-console helps, it all depends on how the modem is connected to the main...
Full answer by scjorge: https://stackoverflow.stackexchange.com/a/66802517 (CC BY-SA 3.0).
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