Quoting myself, to illustrate my point.
1. open, clear skies Garmin reports 7m accuracy, after <1 min. startup of both devices.
View attachment 89519
2. Same day, under tree cover - five minutes after GPS & dashcam startup, actually, the Garmin got a position lock within 90 seconds.
Garmin reports 14m accuracy.
View attachment 89518
The same environment, the same 'on' time, the same windscreen.
The Thinkware is actually far better than the Blackvue which sometimes took 20 minutes, sometimes never to get GPS lock.
Yes, the Garmin is specifically designed to receive GPS signals - but so is the GPS chip in the dashcam. I had an old Garmin 76s that would pick up positional information just fine - inside aircraft, so a thicker than average laminated windscreen with heating elements should not be a challenge, the wet trees above the vehicle in the second photo are clearly attenuating the signal, as shown on the Garmin, but what is received is 'good enough' to determine a valid position within 14 metres.
It seems to be an engineering challenge no-one wants to take on for a 'feature' - but one that dashcams are being sold on.