title: Compute target roll, pitch and yaw angles given initial and target positions and intial roll, pitch and yaw angles
body: <p>I have a model that moves in simulation world. The frame of operation is right handed with X - forward, Y - left and Z - Up. </p>
  
  <p>I know the current position, <code>P1 (x1, y1, z1)</code> and current RPY angles, <code>(R1, P1, Y1)</code>. I have a goal position, <code>P2 (x2, y2, z2)</code>. I would like to move my model from <code>P1</code> to <code>P2</code>. I am stuck at computing the goal RPY angles. I would like my model to turn around first in the direction from P1 to P2 and move in that direction to reach goal.</p>
  
  <p>How do I calculate the target RPY angles, <code>(R2, P2, Y2)</code>, given the above information ?</p>