How do M2 measure distance to an objekt, when you do a quickshot circle ??

not sure exactly your question but i'm going to go out on a limb with a broad reply which is, in general, all distances are measured using gps.

It doesn’t, you set parameters and as long as you don’t touch sticks it will maintain these parameters.

When doing a circle, it doesn't need or do measure distance, it just tracks the object with the camera and keep it centered in front while flying sideways, making a circle in the process.

Like Turbo said above. But I think it goes a bit farther. I think it calculates the radius by noting the rate of angle change required to keep the target in the center of the screen. More angle = closer target. I have no proof of that theory however ;-)