Copter: add requires_position() to mode and rely on the EKF to inform us whether we can fly

Author: andyp1per

ArduCopter/AP_Arming_Copter.cpp

@@ -367,8 +367,18 @@ bool AP_Arming_Copter::gps_checks(bool display_failure)
     fence_requires_gps = (copter.fence.get_enabled_fences() & (AC_FENCE_TYPE_CIRCLE | AC_FENCE_TYPE_POLYGON)) > 0;
 #endif
 
+    // check if we only require position and the EKF thinks we are ok
+    const auto &ahrs = AP::ahrs();
+    char failure_msg[100] = {};
+    if (copter.flightmode->requires_position() && copter.position_ok() && !ahrs.pre_arm_check(true, failure_msg, sizeof(failure_msg))) {
+        check_failed(display_failure, "AHRS: %s", failure_msg);
+        return false;
+    }
+
     // check if flight mode requires GPS
-    bool mode_requires_gps = copter.flightmode->requires_GPS() || fence_requires_gps || (copter.simple_mode == Copter::SimpleMode::SUPERSIMPLE);
+    bool mode_requires_gps = copter.flightmode->requires_GPS() || fence_requires_gps || (copter.simple_mode == Copter::SimpleMode::SUPERSIMPLE)
+                            // skip GPS checks if we only require position and our position is ok
+                            || (copter.flightmode->requires_position() && !copter.position_ok());
 
     // call parent gps checks
     if (mode_requires_gps) {
@@ -647,7 +657,7 @@ bool AP_Arming_Copter::arm_checks(AP_Arming::Method method)
         return false;
     }
 
-    if (!ahrs.ensure_origin_is_set()) {
+    if (copter.flightmode->requires_position() && !ahrs.ensure_origin_is_set()) {
         check_failed(true, "No origin set");
         return false;
     }

ArduCopter/mode.h

@@ -126,6 +126,7 @@ class Mode {
     virtual void exit() {};
     virtual void run() = 0;
     virtual bool requires_GPS() const = 0;
+    virtual bool requires_position() const { return requires_GPS(); }
     virtual bool has_manual_throttle() const = 0;
     virtual bool allows_arming(AP_Arming::Method method) const = 0;
     virtual bool is_autopilot() const = 0;
@@ -991,6 +992,7 @@ class ModeFlowHold : public Mode {
     void run(void) override;
 
     bool requires_GPS() const override { return false; }
+    bool requires_position() const override { return true; }
     bool has_manual_throttle() const override { return false; }
     bool allows_arming(AP_Arming::Method method) const override { return true; };
     bool is_autopilot() const override { return false; }
@@ -1324,7 +1326,8 @@ class ModeLoiter : public Mode {
     bool init(bool ignore_checks) override;
     void run() override;
 
-    bool requires_GPS() const override { return true; }
+    bool requires_GPS() const override { return false; }
+    bool requires_position() const override { return true; }
     bool has_manual_throttle() const override { return false; }
     bool allows_arming(AP_Arming::Method method) const override { return true; };
     bool is_autopilot() const override { return false; }