Scale the compass based on the site area

When the compass has a fixed size, it is either too big for small sites,
or too small for big sites, when using fit view. So the compass adapts
to the ProjectedArea of the Site now.

src/Mod/Arch/ArchSite.py

@@ -282,6 +282,13 @@ class Compass(object):
     def setZOffset(self, offsetInMillimeters):
         from pivy import coin
         self.transform.translation.setValue(0, 0, offsetInMillimeters)
+    
+    def scale(self, area):
+        from pivy import coin
+        
+        scale = round(max(math.sqrt(area.getValueAs("m^2").Value) / 10, 1))
+
+        self.transform.scaleFactor.setValue(coin.SbVec3f(scale, scale, 1))
 
     def setupCoin(self):
         from pivy import coin
@@ -744,6 +751,7 @@ class _ViewProviderSite(ArchFloor._ViewProviderFloor):
 
         self.compass = Compass()
         self.updateCompassVisibility(self.Object)
+        self.updateCompassScale(self.Object)
         self.rotateCompass(self.Object)
 
         vobj.Annotation.addChild(self.compass.rootNode)
@@ -761,6 +769,8 @@ class _ViewProviderSite(ArchFloor._ViewProviderFloor):
             self.updateCompassVisibility(obj)
         elif prop == "CompassRotation":
             self.rotateCompass(obj)
+        elif prop == "ProjectedArea":
+            self.updateCompassScale(obj)
 
     def onChanged(self,vobj,prop):
 
@@ -856,6 +866,12 @@ class _ViewProviderSite(ArchFloor._ViewProviderFloor):
         zOffset = boundBox.ZMax = pos.z
 
         self.compass.setZOffset(zOffset + 1000)
+    
+    def updateCompassScale(self, obj):
+        if not hasattr(self, 'compass'):
+            return
+        
+        self.compass.scale(obj.ProjectedArea)
 
 
 if FreeCAD.GuiUp: