I was going through the ardupilot documentation of HERE + RTK receivers which uses UBLOX M8P module promising of delivering less than 10cm accuracy for a settling time of 2.5hrs. How is that possible? Then what is the difference between survey grade GNSS receivers like Trimble,Novatel and Here + RTK ? How can such a low cost module give centimetre level accuracy? I know the accuracy is limited to certain region (Range of telemetry) but still I have my own doubts. Is there problem with my understanding? Please help me out. Thanks in advance people.
The key is the “RTK”. You might try Google to learn how that technology works
The low end RTK recievers are typically L1 only. Survey grade is always L1 and L2.
There is simply no way you are going to get real accuracy with single frequency (L1) GPS systems.
All survey grade systems use multiple frequencies as well as multiple constellations, and I would be very cautious of claims of great accuracy with single frequency as they have been proved time and time again to just not real.
Here is one discussion
and there are many more discussions if you do a search.
The biggest issue I have seen with single frequency RTK, and this is from discussions, not my own experience, is that it loses lock and takes a very long time to get lock, and then loses it in use.
We are using an AsteRx-m multi frequency which gives a solid lock, even at ground level, and an x/y accuracy of +/- 6mm.