DJI SDK - Fly drone in circular orbit, set the radius (in meters/feet) and Hot Point Mission for Air 2S - dji-sdk

Question

I m trying to fly the drone in circular orbit around the car standing still on the ground.
The drone is flying around the car in circular direction (clockwise) if it is initially placed perpendicular to the front left tyre at a fixed distance. But when the drone is placed on the right or left side of the car, the drone start fly in circular orbit from the point it is placed and that is too off to the car but not around the car as shown in Pic 2.
Pic 1 -
Pic 2 -
this is my code :
var flightController: DJIFlightController?
var timer: Timer?
var radians: Float = 0.0
let velocity: Float = 0.1
#IBAction func actionOrbit(_ sender: Any) {
setupFlightMode()
// Schedule the timer at 2Hz while the default specified for DJI is between 5 and 25Hz
timer = Timer.scheduledTimer(timeInterval: 0.5, target: self, selector: #selector(timerLoop), userInfo: nil, repeats: true)
}
private func setupFlightMode() {
// Reset radians
radians = 0.0
// Invalidate timer if necessary
// This allows switching between flight modes
if timer != nil {
print("invalidating")
timer?.invalidate()
}
}
#objc func timerLoop() {
radians += velocity
if(radians >= 6.283){ //360 degree it will stop the drone once the one orbit is complete
self.timer?.invalidate()
radians = 0.0
self.verticalMoveUpward()
//vertical throttle and then move forward and land
return
}
x = cos(radians)
y = sin(radians)
z = 0
}
private func sendControlData(x: Float, y: Float, z: Float) {
print("Sending x: \(x), y: \(y), z: \(z), yaw: \(yaw)")
// Construct the flight control data object
var controlData = DJIVirtualStickFlightControlData()
controlData.verticalThrottle = z //throttle // in m/s
controlData.roll = x //roll
controlData.pitch = y //pitch
controlData.yaw = self.yaw
// Send the control data to the FC
self.flightController?.send(controlData, withCompletion: { (error: Error?) in
// There's an error so let's stop
if error != nil {
print("Error sending data")
// Disable the timer
self.timer?.invalidate()
}
else{
print("Error sending data \(error.debugDescription)")
}
})
}
The model of the drone I m using : Air 2S
Question 1 :
How can I make the drone fly around the car in circular orbit irrespective of the drone's placement ?
Question 2 :
How can I decide the radius (in meters or feet) of the circular orbit ? Currently every 0.5 seconds it keeps on increasing the radians by 0.1 until it reaches 6.283. Is it something to do with the frequency i.e. 2Hz mentioned in the comment.
Question 3 :
As per the documentation there is Hot Point mission in which the Object can be identified and set. And then the drone can fly in circular orbit around it.
Is it possible for the drone model : Air 2S and if yes how can I provide the radius (in meters) instead of Latitude and Longitude.

Answer 1

If I understand you correct you trying to change the roll and pitch as a function of time?
It will never work. You have to check the drone position and have a pid regulator adjusting for the errors for you desired path.
The gps-pos is fused from gps and imu.
If you have no gps, only imu (maybe sensor) is used and lat/lon=0 from takeoff point.
You will also risc of getting the dji jerky gimbal movement, since it's a flaw in their implementation of virtualstick. Not much to do about that.