robot_control node steering angle 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!

[iluetkeb]

I didn't write the code, but usually with Ackermann steering, the two wheels are not actually using the same angle, but slightly offset to each other. This may be that.