At present the Ardupilot internal representation of GPS values is only to 7 decimal places and cannot give more than +/- 1.5cm accuracy, no matter what system you are using.
We are setting up a much higher accuracy RTK system (+/-6mm) but as the RTK corrections have to go through Ardupilot, which fortunately does not modify the accuracy, so as long as GNSS can do the logging you will get better accuracy. If you are relying on the Ardupilot logs the you are stuck with 1e7 or +/-1.5cm.
I want to reopen this discussion, in order to get more information on how to increase the loiter accuracy in arducopter, I could not find documentation on how to tune and what can be the expected accuracy XYZ from arducopter.
There are lots of documentation of PID tuning, notch filter tuning mag fit tuning etc and tons of forum threads regarding loiter tuning. No need to hijack this thread old.
Could you please point me to a document where it shows how to tune loiter? More precisely what precision can we expect from loiter? Mine sometimes drifts more than 3 meters.
Is it normal for it to be drifting 45cm with rtk on? Is ardupilot GPS still only using 7 decimal places? what kind of precision can we expect from loiter without RTK (Assuming we have a good GPS lock IE 16 sats)
If you could point me in the right direction I would appreciate it, I havent found this documentation online.
What GPS are you using? What fix type are you achieving? RTK Float can be imprecise on the order of meters depending on the proximity and quality of the base station solution.
Geodetic coordinates to 7 decimal places are precise to approximately 1cm. I doubt it’s practical to even try to hold millimeter precise position on any air vehicle (in other words, 7 decimal places is a reasonable practical limit).
I don’t think you’ll find much discussion of expected loiter mode precision because it is nearly impossible to set a reasonable expectation across the wide array of vehicle types and hardware covered by the ArduPilot ecosystem.
I am familiar with that documentation of loiter tunning and its tracking precisely in the logs, so i think tuning is ok.
The GPS im using is HEX Here3+. I also fly some DJIs and I cant help but notice that their loiter performance is much more precise than with my arducopters (although it may be because of visual positioning as well).
I will go throught the links you mentioned. Thanks for the help!
To put it bluntly, the Here3+ uses an M8P module which sucks for precision applications. It’s an excellent general purpose GPS, but its RTK performance has always been weak.
Recommend a newer module that uses an F9P or similar.