AR_AttitudeControl: add get_stopping_distance

libraries/APM_Control/AR_AttitudeControl.cpp

@@ -461,3 +461,18 @@ float AR_AttitudeControl::get_desired_speed() const
     }
     return _desired_speed;
 }
+
+// get minimum stopping distance (in meters) given a speed (in m/s)
+float AR_AttitudeControl::get_stopping_distance(float speed)
+{
+    // get maximum vehicle deceleration
+    const float accel_max = get_accel_max();
+
+    // avoid divide by zero
+    if ((accel_max <= 0.0f) || is_zero(speed)) {
+        return 0.0f;
+    }
+
+    // assume linear deceleration
+    return 0.5f * sq(speed) / accel_max;
+}

libraries/APM_Control/AR_AttitudeControl.h

@@ -92,6 +92,9 @@ public:
     // get latest desired speed recorded during call to get_throttle_out_speed.  For reporting purposes only
     float get_desired_speed() const;
 
+    // get minimum stopping distance (in meters) given a speed (in m/s)
+    float get_stopping_distance(float speed);
+
     // parameter var table
     static const struct AP_Param::GroupInfo var_info[];