When you point on a spot in the screen of your ipad, there's no sense of distance. Like if I am in an open field, and I point at the sky, how does it now when to stop? I don't even know exactly what actual distance I'm pointing at.

I don't think it will work if you just point it at the sky, it needs an object like a tree to lock on to. If your 200 feet high and point it at a tree on the far side of a field it will also decend to the elevation of the object so be carful.

Tap mode is available with p3p?

rob32trk Posted at 2016-4-14 13:06
Tap mode is available with p3p?

As I understand it Tap Fly and Active Track are P4 only

The way I understand "Tap/fly" is that it doesn't know when to stop and if you point to the open sky, it will continue to fly in that direction until you stop it or it flies out of range and does an automatic "Return to Home".  

If you point it at an object, I assume it will continue to fly towards the object until either you stop it or obstacle avoidance takes over.

Loosely speaking...
A) The P4 knows its gimbal orientation. i.e. where the camera is pointed relative to the P4 body.
B) The P4 knows which way it is pointed and its altitude above the ground.  This is from baro, GPS, and mag compass.. these sensors are all fused together to yield the best estimate.
C) The camera is an angle sensor. i.e. a pixel location defines two orthogonal angles from the camera boresight direction.
D) Combining A-C we know the desired heading angle the user has selected on screen.
E) In general, TapFly specifies a heading to fly to, which means one needs to keep on eye on the P4 and stop it when desired. (Obstacle Avoidance will attempt to stop if approaching an obstacle, but its not safe to depend on this feature).
F) If the fly-to angle sends the P4 off to the horizon, and the user doesn't stop it,...it will run low on juice at some point and initiate a RTH.

I like Tap to Fly function, it great to use when you want to make a video of something moving...
but also when you're super LAZY to fly