How come the GPS signal can be disrupted by trees - given that my iPhone can seemingly get a good GPS location under cover, indoors, moving at speed, etc. The only thing that really disrupts an iPhone is a tunnel.
That’s a loaded question. For some light reading, this can help explain a lot about weak GPS and the why. To sum it up, your phone is accurate to a few meters. Your phone uses a bunch of tricks to intuit its location. For example, on the highway it will automatically see the direction you are traveling and that you are in close proximity to a road. Based on the direction of travel it will track the location to the center of the line on the proper side of the road based on the direction the compass and other factors determine you are traveling.
Your Yarbo is trying to maintain accuracy down to a few centimeters. This is much harder to get the precision needed so that it doesn’t exceed the boundaries and NGZ’s. That’s why there are safety buffers built in, so it can account for some of the GPS deviations and other external factors that impact the accuracy. Additionally, Yarbo has a bunch of other sensors to help it when GPS is poor but a lot of those are still being unlocked in software or refined to get more sensor fusion (using them all in concert working together). They are working on this now. It’s called Dead Reckoning. It’s being refined and vastly improved. Additionally, in the near future, it will also use vision (all the cameras) in the future to help cover down in poor GPS areas as well. This is an enhancement to kind of take over for the IMU (Inertial Measurement Unit) and wheel odometry but by using vision. This is called Visual Inertial Odometry (VIO). And hopefully long term we see VSLAM (Visual Simultaneous Location and Mapping).
To answer why it loses GPS by trees, well it loses accuracy (really signal strength) and it becomes noisy as it is blocked, reflected, absorbed, etc by the tree leaves and trunks.
As satellites move in the sky this change in location can help get past what is blocking it so that there is enough of an increase of the CNR (Carrier to Noise Ratio) values enough that the rover has enough confidence to proceed. CNR values above 37 is the minimum for it to proceed as long as there is also enough satellites available to help in the triangulation of its location. Hope that helps clarify things a little.
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Thank you that makes sense.
I had understood that consumer grade GPS was accurate to maybe 10m and that military grade was about 1m (depending on a bunch of factors) - does Yarbo just use GPS for location - or is it also somehow using the base station to increase accuracy? If it is doing that, does that not help out when the Yarbo is under trees?
I’m asking this because the current and most convenient location for my charging station is under some trees. It docks fine - but often I have to manually drive it 10m away from the charging station before it will start a program.
Yes, the data center is what gives it the cm level accuracy. It is the fixed reference point and the rover and DC are constantly communicating. Calculations are done by the rover to compare its location to what the DC is telling it that its location is. Lots of math to get that level of accuracy. But BOTH have to have good GPS and see the same satellites in order for all of these calculations to work. In other words they both have to compare the same set of notes to check their math.
As for the docking station location, you want to pay attention to the diagnostics of the core. Look at the diagnostics and you want to see about 10+ L2 satellites and an Heading DOP of less than 1.5 for a good docking station location. This can vary drastically based on the time of day, weather, angle of the satellites, sunspots, etc. But if you consistently exceed those minimums then it’s not an ideal docking station location. Yarbo recommends 7FT of clearance all around. You can fudge some of that but the further away from a structure you can put it, the better off you will be. Now, the improvements that are coming that I mentioned above will most likely really help here. So you can hang tight and see if when those enhancements are released if it improves your situation. If not, you can consider moving the DS somewhere a little more out in the open. Sometimes it only takes a few inches to get better signal. You can park the core at different locations and watch the diagnostics over the course of the day and see what works best.
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