robot_control node steering computation

[glebos]

Hi,
I am trying to understand the source code of the robot_control_node.

  // Compute state control actions
  // State feedback error 4 position loops / 4 velocity loops 
  // Single steering 
  double d1 =0.0;
  double d = RBCAR_D_WHEELS_M; // divide by 2 for dual Ackermann steering
  double alfa_ref_left = 0.0;
  double alfa_ref_right = 0.0;
  if (alfa_ref_!=0.0) {  // div/0
     d1 =  d / tan (alfa_ref_);
     alfa_ref_left = atan2( d, d1 - 0.105);
     alfa_ref_right = atan2( d, d1 + 0.105);
     if (alfa_ref_<0.0) {
        alfa_ref_left = alfa_ref_left - PI;
        alfa_ref_right = alfa_ref_right - PI;
        }     

I am wondering what (d1 -/+ 0.105) do represent? Could you please explain?
Thank you very much!

[RomanRobotnik]

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