The lady’s not for turning

Around here in the South Cotswold, there are lakes, hundreds of them left behind once the Cotswold stone rocks and gravel have been mined from the ground.  People swim, yacht, canoe, windsurf and powerboat race around the area.  It’d be cool for a piDrone to fly from one side of a lake to the other, tracking the terrain as shown in this gravel pit just 2 minutes walk from my house.  ‘H’ start at the left, move over the pond, climb up and over the gravel and land on the far side:

Surface gravel mining

Surface gravel mining

But there’s a significant problem: neither the ground facing video nor LiDAR work over water.  For the down-facing video, there’s no contrast over the water surface for it to track horizontal movement.  For the LiDAR, the problem come when moving: the piDrone leans to move, and the laser beam doesn’t reflect back to the receiver and height reading stops working.

But there is a solution already in hand that I suspect is easy to implement and has little code performance impact, but amazing impact over the water survival: GPS is currently used in the autopilot process to compare where she is currently located compared to the target location, and pass the speed and direction through to the motion process; it would be nigh on trivial to also pass the horizontal distance and altitude difference since takeoff through to the motion process too.

These fuse with the existing ed*_input code values thus:

  • Horizontally, the GPS fuses always with the down facing PiCamera such that if / when the ground surfaces doesn’t have enough contrast (or she’s travelling too fast for video frames to overlap), the GPS will still keep things moving in the right direction and speed.
  • Vertically is more subtle; as mentioned above, the LiDAR fails when the ground surfaces doesn’t bounce the laser back to the receiver perhaps due to a surface reflection problem or simply because her maximum height of 40m has been exceeded.  In both cases, the LiDAR returns 1cm as the height to report the problem.  Here’s where GPS kicks in, reporting the current altitude since takeoff until the LiDAR starts getting readings again.

Like I’ve said, it’s only a few lines of relatively simple code.  The problem is whether I have the puppies’ plums to try it out over the local lakes?  I am highly tempted, as it’s a lot more real than the object avoidance code for which there will never be a suitable maze.  I think my mind is changing direction rapidly.

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