AP_Common: use singleton to access AP_Terrain data

libraries/AP_Common/Location.cpp

@@ -7,8 +7,6 @@
 #include <AP_AHRS/AP_AHRS.h>
 #include <AP_Terrain/AP_Terrain.h>
 
-AP_Terrain *Location::_terrain = nullptr;
-
 /// constructors
 Location::Location()
 {
@@ -138,7 +136,11 @@ bool Location::get_alt_cm(AltFrame desired_frame, int32_t &ret_alt_cm) const
     float alt_terr_cm = 0;
     if (frame == AltFrame::ABOVE_TERRAIN || desired_frame == AltFrame::ABOVE_TERRAIN) {
 #if AP_TERRAIN_AVAILABLE
-        if (_terrain == nullptr || !_terrain->height_amsl(*this, alt_terr_cm, true)) {
+        AP_Terrain *terrain = AP::terrain();
+        if (terrain == nullptr) {
+            return false;
+        }
+        if (!terrain->height_amsl(*this, alt_terr_cm, true)) {
             return false;
         }
         // convert terrain alt to cm

libraries/AP_Common/Location.h

@@ -2,8 +2,6 @@
 
 #include <AP_Math/AP_Math.h>
 
-class AP_Terrain;
-
 #define LOCATION_ALT_MAX_M  83000   // maximum altitude (in meters) that can be fit into Location structure's alt field
 
 class Location
@@ -35,8 +33,6 @@ public:
     Location(const Vector3f &ekf_offset_neu, AltFrame frame);
     Location(const Vector3d &ekf_offset_neu, AltFrame frame);
 
-    static void set_terrain(AP_Terrain* terrain) { _terrain = terrain; }
-
     // set altitude
     void set_alt_cm(int32_t alt_cm, AltFrame frame);
 
@@ -134,7 +130,6 @@ public:
     static int32_t diff_longitude(int32_t lon1, int32_t lon2);
     
 private:
-    static AP_Terrain *_terrain;
 
     // scaling factor from 1e-7 degrees to meters at equator
     // == 1.0e-7 * DEG_TO_RAD * RADIUS_OF_EARTH