GPS-PPK Accuracy Improvement Needed

[Naterater]

Issue details

Surveyors are using a standalone PPK system instead of ardupilot. All of the hardware is available -- the Here+ and a hotshoe feedback pin are already integrated, however ardupilot does not support the very low latency that is needed for sub-cm geotagging accuracy.

The problems that I am aware of

• CAM event timing at 50Hz
• GPS parsing delay (no PPS signal tracking)
• Cam offsets are not available/tracked
• GPS logs (converted from mission planner) do not contain event timestamps for RTKlib processing (uBlox TM2 messages)
• uBlox UBX-RXM-SFRBX and UBX-TIM-TM2 messages must be logged

Some more discussion about the issue: https://discuss.ardupilot.org/t/here-ppk-and-hotshoe-feedback-processing/26666/8

Version

All

Platform

[ ] All
[ ] AntennaTracker
[x] Copter
[x] Plane
[ ] Rover
[ ] Submarine

Airframe type

AIrframes moving during image capture

Hardware type

Pixhawk, Here+, Hotshoe feedback cable

Logs

N/A

[Saijin-Naib]

This would make my surveys orders of magnitude more robust, and would really make my Solo an even more powerful value proposition.

[rmackay9]

Discussed on the dev call and we think that @bugobliterator is looking into this.
This PR is related: #8409