So far, I’ve been looking at LiDAR sensors
- the LEDDAR One gives me quadframe z-axis height and with differentiation, velocity
- the Scanse sweep gives a 360° quadframe x- and y-axis plot of the borders of the flight area; to turn that into something useful is going to require more processing; something along the lines of using the known pitch, roll and yaw gyros to rotate the previous scan into the current scan frame, and then compare the misalignment between the two to guesstimate movement direction and speed. It’s not clear yet how much of this will be provided by the Scance processing and how much I’ll have to do, but a 360° scan feels like a lot of data to process.
My friend in China is using the equivalent of a PX4FLOW optical flow sensor: a downward facing low resolution camera with gyro and URF. Like I described above, with the height and the incremental angles from the gyro, they process picture frame changes to come up with horizontal velocities – critically, the PX4FLOW is doing this, and spitting out velocities over I2C. Follow the link and page down to the “Accuracy” section to see how well the tracking works for a manually controlled flight; the integrated-velocities distance / direction plot of the flight path overlayed on the satellite image is a very convincing match.
A long time ago, in a galaxy far far away, I’d seen the PX4FLOW, seen its price and moved on. But now, I’m starting to wonder whether I should think again.
Having said that, perhaps with scanse, I could do the same, but much simplified by only matching the outline of the flight space rather 2 photos of the same space. And perhaps I can break this down into small enough pieces that a whole outline can be processed in pieces during 100 motion periods (i.e. 1s). This is starting to feel viable and is a lot more aligned with my DIY desire rather than buying a PX4FLOW that does it all for me.