wait for the servo to reach Xobject?

detection motion with moving camera is still beyond achievement, so if I want to move the camera to new position and continue detection what should I do? after detecting moving object in the scene and having the xy and speed of it, I can predict its new location after time and I can give order to servo motor to move until reaching this point. But: how can I pause the code until reaching this point and still moving the servo until Xdesired-Xcentre=0 ? I'm not giving the servo precise value to do it, i just order it to move until reaching.