Add upside-down icon for NorthArrow

CityDoctorParent/Extensions/CityDoctorGUI/src/main/java/de/hft/stuttgart/citydoctor2/gui/MainWindow.java

@@ -237,6 +237,9 @@ public class MainWindow extends Application {
     @FXML
     private Label availableLabel;
 
+    private Image north;
+    private Image northFlip;
+
     private Group meshGroup;
 
     private Group world;
@@ -858,7 +861,8 @@ public class MainWindow extends Application {
         meshGroup = new Group();
         world.getChildren().add(meshGroup);
 
-        Image north = new Image(getClass().getResourceAsStream("icons/north.png"));
+        north = new Image(getClass().getResourceAsStream("icons/north.png"));
+        northFlip = new Image(getClass().getResourceAsStream("icons/north_flip.png"));
         northArrow = new ImageView(north);
         northArrow.setFitHeight(50);
         northArrow.setFitWidth(50);
@@ -940,8 +944,19 @@ public class MainWindow extends Application {
         double absRotZ = cameraZRotation.getAngle() - 360 * Math.floor(cameraZRotation.getAngle() / 360);
         double absRotX = cameraXRotation.getAngle() - 360 * Math.floor(cameraXRotation.getAngle() / 360);
 
-        double northRot = ((80 <= absRotX && absRotX <= 260) ?  360-absRotZ: (absRotZ+180)%360 );
-
+        double northRot;
+        if (80 <= absRotX && absRotX <= 260){
+           northRot =  360-absRotZ;
+            if (northArrow.getImage() != north){
+                northArrow.setImage(north);
+            }
+        } else {
+            //Camera is below horizon line -> flip north arrow horizontally
+           northRot = (absRotZ+180)%360;
+           if (northArrow.getImage() != northFlip){
+               northArrow.setImage(northFlip);
+           }
+        }
         northArrow.setRotate(northRot);
     }