Even though GPS makes it possible for us to easily navigate around the planet in almost any vehicle we’d like, whether that’s a passenger vehicle, airplane, or cargo ship, it’s not really suitable for applications that require sub-meter accuracy. For that, some specialized hardware is needed, and [GreatScott!] shows us how to do it using a small robot as a platform.
The key to extremely accurate GPS signals in this case is using a receiver that supports real-time kinematic positioning (RTK). This type of system relies on a base station with a known position communicating with local mobile receivers to increase the precision of those mobile receivers by comparing the phase angle of the received signals. Of course these modules are much more expensive than the average standard GPS receiver, but for this kind of accuracy there is always a cost.
After getting a baseline accuracy of around two meters with a standard GPS receiver, [GreatScott!] installs the RTK GPS mobile receiver on a tracked robotic platform and a base station on a fence post. With the RTK system running, the limiting factor in accuracy became the robot’s steering system, as its turning radius and steering algorithms weren’t up to the task of hitting centimeter-sized targets out of the box.
But, as a proof-of-concept, it goes to show how accurate GPS can be as long as the right hardware is used, and for practical applications is good enough to mow a lawn with a robot or even do some amateur land surveying.
How about this?
Set up a fixed GPS receiver on the property. Log GPS data over days or weeks, average all the data, and call the resulting, composite, value your “reference” location value. After that, take every GPS live reading and subtract the reference value, to generate a stream of error-correction values.
Next, set up a radio link (Meshtastic?) and transmit the time-stamped error correction stream to the robot. Every time the robot makes a GPS measurement, subtract the received error correction value.
It would be interesting to see to what extent the robot’s positional accuracy improves.
I was thinking I’m same thing, if the distance is short enough. ESP-NOW could work.
The usual method is to have a receiver at a known (surveyed) location. It can then calculate the difference between the pseudo range (time of flight) data from each SV and what is expected. These differential updates are then transmitted to another receiver. Many/most GPS receivers can accept this data.
No RTK required.
Great news, that is already a thing! It’s called Differential GPS, and there are companies and services that provide local correction, but you could absolutely build your own. Unfortunately, accuracy when one receiver is in motion is rarely better than 1-2 meters so not good enough for this type of work.
Part of the problem is it can only correct for signal “errors” and not errors within the receiver itself. My understanding is that RTK receivers are expensive in part because you have two receivers with identical signal paths and both are built to detect phase differences on the order of 10-50 pico seconds to get single-digit cm accuracy. For comparison, my cheap ($100) GPS gear can get below 10 nano seconds but that is still ~3 meters worst case.
IMHO a better answer with lawn bots is a fusion of systems that compliment each other. GPS provides bulk / approximate positioning at large area and something else (UWB, photogrammetry, etc.) provides high accuracy position within a smaller (backyard) area.