AP_Rally: tidy creation of Location from RallyLocation

libraries/AP_Rally/AP_Rally.cpp

@@ -122,18 +122,17 @@ bool AP_Rally::set_rally_point_with_index(uint8_t i, const RallyLocation &rallyL
 // helper function to translate a RallyLocation to a Location
 Location AP_Rally::rally_location_to_location(const RallyLocation &rally_loc) const
 {
-    Location ret = {};
-
-    // we return an absolute altitude, as we add homeloc.alt below
-    ret.relative_alt = false;
-
-    //Currently can't do true AGL on the APM.  Relative altitudes are
-    //relative to HOME point's altitude.  Terrain on the board is inbound
-    //for the PX4, though.  This line will need to be updated when that happens:
-    ret.alt = (rally_loc.alt*100UL) + AP::ahrs().get_home().alt;
+    //Relative altitudes are relative to HOME point's altitude:
+    Location ret {
+        rally_loc.lat,
+        rally_loc.lng,
+        rally_loc.alt * 100,
+        Location::AltFrame::ABOVE_HOME
+    };
 
-    ret.lat = rally_loc.lat;
-    ret.lng = rally_loc.lng;
+    // notionally the following call can fail, but we have no facility
+    // to return that fact here:
+    ret.change_alt_frame(Location::AltFrame::ABSOLUTE);
 
     return ret;
 }