Don't know if this has been thought of and dismissed or not. How about using the IMU as an INS.
I think most of us are expecting higher accuracy than is possible while keeping cost down. We also have a problem with perception of error due to scale. Baro and GPS errors are acceptable in full scale but seem huge for our small toys.
My proposal is to use baro and gps only for waypoints and then switch over to INS to maintain position. This would also allow the copter to fight the wind better. The stick would then become purely rate based for speed unless in acro mode, just like FBW in APM. The IMU already has the accuracy as is evidenced by the multitude of indoor videos show a perfectly stationary copter. Sonar is still the best choice for low level ground avoidance.
A possible addition some time in the distant future (AC4 or5) would be to add INS based missions to allow circus tricks like flying through hoops. The board could possibly even be placed in learn mode and a short indoor mission walked through by hand so it can learn to put on a show.
Is any of this possible? Don't know. Just my thoughts.
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We did it, thought, after 1.5 years of work. It is called IMU+Ultrasonic sensor fusion and is available in our Precise (±2cm) Indoor Positioning system in NIA configuration. It requires that ultrasonic-based location update is not less than 4Hz. When available, you can precise IMU (INS) based tracking with 100Hz update rate and latency of 12-15ms on board of a drone or robot.
https://marvelmind.com/
Yes I did mean just using dead reckoning. So I correctly assumed that current affordable hardware is still not up to the task. By the sounds of it maybe AC4 or 5 is still optimistic, maybe version 10 in a few years, Having been involved with the avionics research industry, I realise how long things can take. It took something like 35 years from a FBW plane to the first completely FBW helicopter with no mechanical backup. What we have now was only a dream not that long ago.
Thanks.
Any videos showing great stability indoors owe that stability to ultrasonic and infrared sensors and lack of wind. And those videos of quads flying through hoops etc were done using external multicamera optical imaging systems costing six figures plus. If you think the precision using baro alt is bad, wait till you try doing a double integration with our low cost accelerometers. An accurate INS solution with this level of gyro and accelerometer sensors is not possible. If it were as simple as designing a good Kalman filter it would have been done long ago.