AP_OpticalFlow: Add support for fixed height optical flow

libraries/AP_OpticalFlow/AP_OpticalFlow.cpp

@@ -93,6 +93,15 @@ const AP_Param::GroupInfo AP_OpticalFlow::var_info[] = {
     // @User: Advanced
     AP_GROUPINFO("_ADDR", 5,  AP_OpticalFlow, _address,   0),
 
+    // @Param: _HGT_OVR
+    // @DisplayName: Height override of sensor above ground
+    // @Description: This is used in rover vehicles, where the sensor is a fixed height above the ground
+    // @Units: m
+    // @Range: 0 2
+    // @Increment: 0.01
+    // @User: Advanced
+    AP_GROUPINFO_FRAME("_HGT_OVR", 6,  AP_OpticalFlow, _height_override,   0.0f, AP_PARAM_FRAME_ROVER),
+
     AP_GROUPEND
 };
 
@@ -259,7 +268,8 @@ void AP_OpticalFlow::update_state(const OpticalFlow_state &state)
                                 _state.flowRate,
                                 _state.bodyRate,
                                 _last_update_ms,
-                                get_pos_offset());
+                                get_pos_offset(),
+                                get_height_override());
     Log_Write_Optflow();
 }
 

libraries/AP_OpticalFlow/AP_OpticalFlow.h

@@ -100,6 +100,9 @@ public:
     // last_update() - returns system time of last sensor update
     uint32_t last_update() const { return _last_update_ms; }
 
+    // get_height_override() - returns the user-specified height of sensor above ground
+    float get_height_override() const { return _height_override; }
+
     struct OpticalFlow_state {
         uint8_t  surface_quality;   // image quality (below TBD you can't trust the dx,dy values returned)
         Vector2f flowRate;          // optical flow angular rate in rad/sec measured about the X and Y body axis. A RH rotation about a sensor axis produces a positive rate.
@@ -135,6 +138,7 @@ private:
     AP_Int16 _yawAngle_cd;          // yaw angle of sensor X axis with respect to vehicle X axis - centi degrees
     AP_Vector3f _pos_offset;        // position offset of the flow sensor in the body frame
     AP_Int8  _address;              // address on the bus (allows selecting between 8 possible I2C addresses for px4flow)
+    AP_Float  _height_override;              // height of the sensor above the ground. Only used in rover
 
     // method called by backend to update frontend state:
     void update_state(const OpticalFlow_state &state);