AP_AHRS: made a few methods const

libraries/AP_AHRS/AP_AHRS.h

@@ -85,7 +85,7 @@ public:
     float get_roll_rate_earth(void);
 
     // return a smoothed and corrected gyro vector
-    virtual Vector3f get_gyro(void) = 0;
+    virtual const Vector3f get_gyro(void) const = 0;
 
     // return the current estimate of the gyro drift
     virtual Vector3f get_gyro_drift(void) = 0;
@@ -109,7 +109,7 @@ public:
 
     // return a DCM rotation matrix representing our current
     // attitude
-    virtual Matrix3f get_dcm_matrix(void) = 0;
+    virtual const Matrix3f get_dcm_matrix(void) const = 0;
 
     // get our current position, either from GPS or via
     // dead-reckoning. Return true if a position is available,

libraries/AP_AHRS/AP_AHRS_DCM.h

@@ -25,10 +25,10 @@ public:
     }
 
     // return the smoothed gyro vector corrected for drift
-    Vector3f        get_gyro(void) {
+    const Vector3f get_gyro(void) const {
         return _omega + _omega_P + _omega_yaw_P;
     }
-    Matrix3f        get_dcm_matrix(void) {
+    const Matrix3f        get_dcm_matrix(void) const {
         return _dcm_matrix;
     }
 

libraries/AP_AHRS/AP_AHRS_HIL.h

@@ -8,11 +8,11 @@ public:
     AP_AHRS_HIL(AP_InertialSensor *ins, GPS *&gps) : AP_AHRS(ins, gps) {}
 
     // Accessors
-    Vector3f get_gyro(void) {
+    const Vector3f get_gyro(void) const {
         return _omega;
     }
 
-    Matrix3f get_dcm_matrix(void) {
+    const Matrix3f get_dcm_matrix(void) const {
         Matrix3f m;
         m.from_euler(roll, pitch, yaw);
         return m;

libraries/AP_AHRS/AP_AHRS_MPU6000.h

@@ -40,11 +40,11 @@ public:
     void init();
 
     // return the smoothed gyro vector corrected for drift
-    Vector3f get_gyro(void) {
+    const Vector3f get_gyro(void) const {
         return _ins->get_gyro();
     }
 
-    Matrix3f get_dcm_matrix(void) {
+    const Matrix3f get_dcm_matrix(void) const {
         return _dcm_matrix;
     }