blue_q has sent me a .map-file on my request - thank you for your help, blue_q!
The file is a proprietary binary format, nothing that I have ever seen. It seems to be even specific for DVRs, as it contains references to a .mov file.
As far as I understand, it does contain a time stamp, but I am not sure what it is. Probably terrestrial time, loosely related but not equal to UTC. But I can only suppose that for now. There seems to be, apart from the position, at least another three-digit tag, which could be speed or track (direction).
I have not yet managed to decode it. For decoding it, I will need further information and data. I don`t want to bother you both, so I placed another order again. Lets see if I`ll get my hands on a unit this time.
Above, there is a link to another camera, DashCamMan supposes it to have simlar hardware. Even in the sample video, the GPS longitude is slightly off: the video has probably been taken in Canada, the GPS position overlay shows a position the italian alps...
I don`t know where the video has been taken exactly, but a latitude error of +90 degrees comes to mind when used on the western hemisphere (negative latitude).
The overlay shows position, speed, and another value (012) that I cannot interpret. It doesn`t seem to be track/direction, as it remains fixed even if the car turns 90 degrees. It could be the number of satellites acquired, but i that doubt acquiring 12 satellites in the same geographic position would be possible.
It would be very helpful having a video or at least a screenshot at hand that shows the video with GPS overlay data (position, speed, whatever), the corresponding .map file and maybe a NMEA track log or similar of another GPS receiver. --> Could someone please post a screenshot?
For my own use, having a speed tag on the screen will be sufficient, but obviously I will try to decode the format, as I want my data to be accessible without special software.
There is another possible drawback: if the GPS position overlay is way off, and the speed tag updating only with a delay of more than very few seconds (one to two seconds is normal), then the police or a judge may eventually discard the whole video as inappropriate for evidence.
In this case, the only useful application of GPS in this unit would be having the clock synchronised automatically - if it works.
Maybe -without having investigated the details yet- it is advisable to choose another logger or logging DVR if GPS data is really important.