Rover: attempt to set home position regardless of GPS lock

The AHRS may be supplying as a home position through mechanisms other
than a GPS lock.  Don't assume in the caller to update_home().

Rover: fold update_home_from_EKF back into sole caller

This method is confusingly similarly named to update_home - and they do
pretty much the opposite thing.

Rover: remove incorrect and misleading comments on set_home_to_current_location

Rover: rewrite update_home to not set home if no origin set

Also checks that home is set before using values from it

Rover: zero stack variables when updating home

If these are a problem we have significant problems through the code

APMrover2/APMrover2.cpp

@@ -164,8 +164,10 @@ void Rover::ahrs_update()
     // update position
     have_position = ahrs.get_position(current_loc);
 
-    // update home from EKF if necessary
-    update_home_from_EKF();
+    // set home from EKF if necessary and possible
+    if (!ahrs.home_is_set()) {
+        set_home_to_current_location(false);
+    }
 
     // if using the EKF get a speed update now (from accelerometers)
     Vector3f velocity;
@@ -281,10 +283,8 @@ void Rover::one_second_loop(void)
     // cope with changes to mavlink system ID
     mavlink_system.sysid = g.sysid_this_mav;
 
-    // update home position if not soft armed and gps position has
-    // changed. Update every 1s at most
-    if (!hal.util->get_soft_armed() &&
-        gps.status() >= AP_GPS::GPS_OK_FIX_3D) {
+    // attempt to update home position and baro calibration if not armed:
+    if (!hal.util->get_soft_armed()) {
         update_home();
     }
 

APMrover2/Rover.h

@@ -406,7 +406,6 @@ private:
     void update_mission(void);
 
     // commands.cpp
-    void update_home_from_EKF();
     bool set_home_to_current_location(bool lock);
     bool set_home(const Location& loc, bool lock);
     void update_home();

APMrover2/commands.cpp

@@ -1,21 +1,8 @@
 #include "Rover.h"
 
-// checks if we should update ahrs home position from the EKF's position
-void Rover::update_home_from_EKF()
-{
-    // exit immediately if home already set
-    if (ahrs.home_is_set()) {
-        return;
-    }
-
-    // move home to current ekf location (this will set home_state to HOME_SET)
-    set_home_to_current_location(false);
-}
-
-// set ahrs home to current location from EKF reported location or GPS
+// set ahrs home to current location from inertial-nav location
 bool Rover::set_home_to_current_location(bool lock)
 {
-    // use position from EKF if available otherwise use GPS
     Location temp_loc;
     if (ahrs.have_inertial_nav() && ahrs.get_position(temp_loc)) {
         if (!set_home(temp_loc, lock)) {
@@ -40,12 +27,6 @@ bool Rover::set_home(const Location& loc, bool lock)
         return false;
     }
 
-    // check if EKF origin has been set
-    Location ekf_origin;
-    if (!ahrs.get_origin(ekf_origin)) {
-        return false;
-    }
-
     const bool home_was_set = ahrs.home_is_set();
 
     // set ahrs home
@@ -79,20 +60,27 @@ bool Rover::set_home(const Location& loc, bool lock)
     return true;
 }
 
-/*
-  update home location from GPS
-  this is called as long as we have 3D lock and the arming switch is
-  not pushed
-*/
+// called periodically while disarmed to update our home position to
+// our current location
 void Rover::update_home()
 {
-    if (!ahrs.home_is_locked()) {
-        Location loc;
-        if (ahrs.get_position(loc)) {
-            if (get_distance(loc, ahrs.get_home()) > DISTANCE_HOME_MAX) {
-                ahrs.set_home(loc);
-            }
-        }
+    if (ahrs.home_is_locked()) {
+        // we've been explicitly told our home location
+        return;
     }
+
+    Location loc{};
+    if (!ahrs.get_position(loc)) {
+        return;
+    }
+
     barometer.update_calibration();
+
+    if (ahrs.home_is_set() &&
+        get_distance(loc, ahrs.get_home()) < DISTANCE_HOME_MINCHANGE) {
+        // insufficiently moved from current home - don't change it
+        return;
+    }
+
+    ahrs.set_home(loc);
 }

APMrover2/defines.h

@@ -109,7 +109,7 @@ enum fs_ekf_action {
     FS_EFK_HOLD = 1
 };
 
-#define DISTANCE_HOME_MAX 0.5f  // Distance max to home location before changing it when disarm
+#define DISTANCE_HOME_MINCHANGE 0.5f  // minimum distance to adjust home location
 
 enum mode_reason_t {
     MODE_REASON_INITIALISED = 0,