The experience of Matthew Griffin matches mine. However – when we can measure for a fair period of time two things have helped us calibrate this better.
We did have to wrap a simple (kalman) filter on the antenna orientation and the IMU to get a rough running commentary though – and this is not very CPU or battery light.
- Using the IMU you get a fair idea of the distance/direction of travel – and if this is over a short period of time – we assume the other ‘side’ is stationary. This helps a lot to get a value for ‘current’ orientation and ‘callibrate current environment noise.
- Likewise – do the same for rotations/position changes.
We’ve found that in general a re-orientation of the device is a better way to get direction; and that distance is only reliable some up to some 30 to 600 seconds after a ‘move’ calibration’ and only if the device is not too much rotated. And in practice once needs some 4-5 ‘other’ devices; ideally not too mobile, to keep oneself dynamically calibrated.
However the converse is quite reliable – i.e. we know when not to measure. And the net result is that one can fairly well ascertain things like ‘at the keyboard’ and ‘relocated’/moved away through a specific door/openning or direction. Likewise measuring a field by randomly dancing through the room; changing orientation a lot – does work well once the receiver antenna lobes got somewhat worked out after a stationary period.