AC_WPNav: add TER_MARGIN param

libraries/AC_WPNav/AC_WPNav.cpp

@@ -75,6 +75,14 @@ const AP_Param::GroupInfo AC_WPNav::var_info[] = {
     // @User: Standard
     AP_GROUPINFO("JERK",   11, AC_WPNav, _wp_jerk, 1.0f),
 
+    // @Param: TER_MARGIN
+    // @DisplayName: Waypoint Terrain following altitude margin
+    // @Description: Waypoint Terrain following altitude margin.  Vehicle will stop if distance from target altitude is larger than this margin (in meters)
+    // @Units: m
+    // @Range: 0.1 100
+    // @User: Advanced
+    AP_GROUPINFO("TER_MARGIN",  12, AC_WPNav, _terrain_margin, 10.0),
+
     AP_GROUPEND
 };
 

libraries/AC_WPNav/AC_WPNav.h

@@ -52,6 +52,9 @@ public:
     // get terrain's altitude (in cm above the ekf origin) at the current position (+ve means terrain below vehicle is above ekf origin's altitude)
     bool get_terrain_offset(float& offset_cm);
 
+    // return terrain following altitude margin.  vehicle will stop if distance from target altitude is larger than this margin
+    float get_terrain_margin() const { return MAX(_terrain_margin, 0.1); }
+
     // convert location to vector from ekf origin.  terrain_alt is set to true if resulting vector's z-axis should be treated as alt-above-terrain
     //      returns false if conversion failed (likely because terrain data was not available)
     bool get_vector_NEU(const Location &loc, Vector3f &vec, bool &terrain_alt);
@@ -240,6 +243,7 @@ protected:
     AP_Float    _wp_accel_cmss;         // horizontal acceleration in cm/s/s during missions
     AP_Float    _wp_accel_z_cmss;       // vertical acceleration in cm/s/s during missions
     AP_Float    _wp_jerk;               // maximum jerk used to generate scurve trajectories in m/s/s/s
+    AP_Float    _terrain_margin;        // terrain following altitude margin. vehicle will stop if distance from target altitude is larger than this margin
 
     // scurve
     SCurve _scurve_prev_leg;            // previous scurve trajectory used to blend with current scurve trajectory