Better handling a mission altitude default

* If new Survey is set to altitude fixed value then use mission default
altitude
* If the user applies a new altitude to the entire mission change
surveys to fixed altitude and apply altitude

src/MissionManager/SurveyMissionItem.cc

@@ -14,6 +14,8 @@
 #include "QGCGeo.h"
 #include "QGroundControlQmlGlobal.h"
 #include "QGCQGeoCoordinate.h"
+#include "SettingsManager.h"
+#include "AppSettings.h"
 
 #include <QPolygonF>
 
@@ -117,6 +119,11 @@ SurveyMissionItem::SurveyMissionItem(Vehicle* vehicle, QObject* parent)
         _turnaroundDistFact.setRawValue(5);
     }
 
+    // We override the grid altitude to the mission default
+    if (_manualGridFact.rawValue().toBool() || _fixedValueIsAltitudeFact.rawValue().toBool()) {
+        _gridAltitudeFact.setRawValue(qgcApp()->toolbox()->settingsManager()->appSettings()->defaultMissionItemAltitude()->rawValue());
+    }
+
     connect(&_gridSpacingFact,                  &Fact::valueChanged,                        this, &SurveyMissionItem::_generateGrid);
     connect(&_gridAngleFact,                    &Fact::valueChanged,                        this, &SurveyMissionItem::_generateGrid);
     connect(&_gridEntryLocationFact,            &Fact::valueChanged,                        this, &SurveyMissionItem::_generateGrid);
@@ -1361,6 +1368,7 @@ double SurveyMissionItem::_turnaroundDistance(void) const
 
 void SurveyMissionItem::applyNewAltitude(double newAltitude)
 {
+    _fixedValueIsAltitudeFact.setRawValue(true);
     _gridAltitudeFact.setRawValue(newAltitude);
 }