Steering.h

00001 
00002 #define PI 3.141592653589
00003 
00004 /** A class for managing steering angle calculations based on current and desired heading
00005  *  and specified intercept distance along the new path.  
00006  *
00007  *  See Notebook entry: http://mbed.org/users/shimniok/notebook/smooth-steering-for-rc-car/
00008  */
00009 class Steering
00010 {
00011   public:
00012     /** create a new steering calculator
00013      *
00014      * @param wheelbase vehicle wheelbase
00015      * @param track vehicle track width
00016      * @param intercept new course intercept distance
00017      */
00018     Steering(float wheelbase, float track);
00019 
00020     /** set intercept distance
00021      * @param intercept distance along new course at which turn arc will intercept
00022      */
00023     void setIntercept(float intercept);
00024 
00025     /** convert course change to average steering angle
00026      * assumes Ackerman steering, with track and wheelbase
00027      * and course intercept distance specified.
00028      *
00029      * See notebook: http://mbed.org/users/shimniok/notebook/smooth-steering-for-rc-car/
00030      *
00031      * @param theta relative bearing of the new course
00032      * @returns steering angle in degrees
00033      */ 
00034     float calcSA(float theta);
00035 
00036     /** convert course change to average steering angle
00037      * assumes Ackerman steering, with track and wheelbase
00038      * and course intercept distance specified. Also, |radius| of turn is limited to limit
00039      *
00040      * See notebook: http://mbed.org/users/shimniok/notebook/smooth-steering-for-rc-car/
00041      *
00042      * @param theta relative bearing of the new course
00043      * @param limit is the limit of the turn circle radius (absolute value)
00044      * @returns steering angle in degrees
00045      */ 
00046     float calcSA(float theta, float limit);
00047 
00048     /** compute steering angle based on pure pursuit algorithm
00049      */
00050     float purePursuitSA(float hdg, float Bx, float By, float Ax, float Ay, float Bx, float By);
00051     
00052     /** Compute cross track error given last waypoint, next waypoint, and robot coordinates
00053      * @returns cross track error
00054      */
00055     float crossTrack(float Bx, float By, float Ax, float Ay, float Bx, float By);
00056     
00057   private:
00058 
00059     inline static float angle_radians(float deg) {return (PI/180.0)*deg;}
00060 
00061     inline static float angle_degrees(float rad) {return (180/PI)*rad;}
00062 
00063     float _wheelbase;
00064     float _track;
00065     float _intercept;
00066 };