"Not defending them (for fear of getting caught in a crossfire), but it looks like they do include GPS in their size calc. And they have all the stuff on board (IMU stuff and pressure) as well. Don't know how "big" (length, area,…"

"Good stuff Ryan...even with magnetometers, wind estimation is important for better path following and auto landings. Since you have all this information however, is the EKF possibly a little overkill? Since most GPS give you NED velocity (Ublox…"

"Hi Jason, Not sure, but they probably are just giving you the arctan of their velocity vectors, since that it needed for the calc anyway. Take a stream of data and compare the two (atan2 of velocity and their reported heading) in a walking test down…"

"Sorry, didn't realize Bill had previously posted the description (which is what I was describing less eloquently above). Seems like you have your answer then :)"

"You're right, the accel doesn't measure gravity, but in steady flight it measures the acceleration from other sources that keep it steady in the gravitational field. If you aren't accelerating (back to my discussion about the unit…"

"Hi Roy, That makes it more clear what you were asking. Do the thought experiment again but tilt the unit. It still works. Your X and Y sensors will measure the tilt of the craft, they are just noisy. A 10 degree tilt is only about 2/10ths of a g…"

"Looking at the data, it all looks correct. The noise levels are pretty close to each other. Noise happens. Hovering things are kind of easier to think about than normal aircraft I think. Bills note looks right, here is another thought…"

"Looks great! Usually the Euler singularity lock is at 90 degrees pitch up or down, not the roll axis, but I'm assuming you don't have that problem either. How much is this going to cost and when do you think it will be out??"