disable min loiter altitude

src/modules/navigator/mission.cpp

@@ -1131,8 +1131,17 @@ Mission::do_abort_landing()
 	// loiter at the larger of MIS_LTRMIN_ALT above the landing point
 	//  or 2 * FW_CLMBOUT_DIFF above the current altitude
 	float alt_landing = get_absolute_altitude_for_item(_mission_item);
-	float alt_sp = math::max(alt_landing + _param_loiter_min_alt.get(),
-				 _navigator->get_global_position()->alt + (2 * _param_fw_climbout_diff.get()));
+
+	// ignore _param_loiter_min_alt if smaller then 0 (-1)
+	float alt_sp;
+
+	if (_param_loiter_min_alt.get() > 0.0f) {
+		alt_sp = math::max(alt_landing + _param_loiter_min_alt.get(),
+				   _navigator->get_global_position()->alt + (2 * _param_fw_climbout_diff.get()));
+
+	} else {
+		alt_sp = math::max(alt_landing, _navigator->get_global_position()->alt + (2 * _param_fw_climbout_diff.get()));
+	}
 
 	_mission_item.nav_cmd = NAV_CMD_LOITER_UNLIMITED;
 	_mission_item.altitude_is_relative = false;

src/modules/navigator/mission_block.cpp

@@ -571,9 +571,15 @@ MissionBlock::mission_item_to_position_setpoint(const struct mission_item_s *ite
 		break;
 
 	case NAV_CMD_LOITER_TO_ALT:
+
 		// initially use current altitude, and switch to mission item altitude once in loiter position
-		sp->alt = math::max(_navigator->get_global_position()->alt,
-				    _navigator->get_home_position()->alt + _param_loiter_min_alt.get());
+		if (_param_loiter_min_alt.get() > 0.0f) { // ignore _param_loiter_min_alt if smaller then 0 (-1)
+			sp->alt = math::max(_navigator->get_global_position()->alt,
+					    _navigator->get_home_position()->alt + _param_loiter_min_alt.get());
+
+		} else {
+			sp->alt = _navigator->get_global_position()->alt;
+		}
 
 	// fall through
 	case NAV_CMD_LOITER_TIME_LIMIT:

src/modules/navigator/mission_params.c

@@ -61,15 +61,16 @@ PARAM_DEFINE_FLOAT(MIS_TAKEOFF_ALT, 2.5f);
  * Minimum Loiter altitude
  *
  * This is the minimum altitude the system will always obey. The intent is to stay out of ground effect.
+ * set to -1, if there shouldn't be a minimum loiter altitude
  *
  * @unit m
- * @min 0
+ * @min -1
  * @max 80
  * @decimal 1
  * @increment 0.5
  * @group Mission
  */
-PARAM_DEFINE_FLOAT(MIS_LTRMIN_ALT, 1.2f);
+PARAM_DEFINE_FLOAT(MIS_LTRMIN_ALT, -1.0f);
 
 /**
  * Persistent onboard mission storage