Okay, lets brainstorm.
You've seen the system used by DJI (you can check some youtube videos), which is able to hold a fixed position (x, y, z), reasonably well. It achieves this using GPS (when outdoors) and multiple cameras.
The closest thing we have to this on the Erle Brain (EB) is GPS (just like DJI) and also the px4flow. The problem is that the px4flow does not work on the EB.
Lidarlite already allows us to hold z axis accurately, though I have not been able to get this to work on my EB2.
So, you have 2 options:
1, switch to a different flight controller (which I personally, am trying to avoid, but I may be forced to do this).
2, develop own system of having 3 cameras fixed onto the copter and create software to read the image from each camera. If the image shifts, the copter should be moved into a position, such that the new camera images match the original camera images.
The cameras used can be cheap (low res), so the cost will be low.
Option 2 will be the most ambitious and will give absolute control (because we have the source code) and should work nicely indoors and outdoors.
What do you think?
Also, do you have any videos of your copter using lidarlite to h old altitude?