needle from magnetometer

flockompass.kv

@@ -27,6 +27,7 @@
             on_map_relocated: centermark.lat = mapview.lat; centermark.lon = mapview.lon
 
             MapMarker:
+                source: 'marker.png'
                 id: centermark
                 anchor_x: 0.2
                 anchor_y: 0.3
@@ -74,6 +75,48 @@
             Label:
                 text: str(root.z_calib) + ')'
 
+        Label:
+            text: app.gps_location
+
+        Label:
+            text: app.gps_status
+
+        BoxLayout:
+            size_hint_y: None
+            height: '48dp'
+            padding: '4dp'
+
+            ToggleButton:
+                text: 'Start' if self.state == 'normal' else 'Stop'
+                on_state:
+                    app.start(1000, 0) if self.state == 'down' else \
+                    app.stop()
+
+
+        FloatLayout:
+
+            canvas:
+                Color:
+                    rgb: .98, .98, .98
+                Rectangle:
+                    size: self.size
+        
+            Image:
+                source: 'rose.png'
+        
+            Image:
+                source: 'needle.png'
+        
+                canvas.before:
+                    PushMatrix
+                    Rotate:
+                        angle: root.needle_angle
+                        axis: 0, 0, 1
+                        origin: self.center
+        
+                canvas.after:
+                    PopMatrix
+                            
     # BoxLayout:
     #     orientation: 'vertical'
     #     canvas:
@@ -108,4 +151,3 @@
 
     #     Label:
     #         text: app.gps_status
-                    

main.py

@@ -7,7 +7,9 @@ from kivy_garden.mapview import MapView
 from plyer import gps
 from kivy.clock import mainthread
 from kivy.utils import platform
-
+from kivy.vector import Vector
+from kivy.animation import Animation
+from math import floor
 
 
 class MapScreen(Screen):
@@ -20,17 +22,39 @@ class CompassScreen(Screen):
     x_calib = NumericProperty(0)
     y_calib = NumericProperty(0)
     z_calib = NumericProperty(0)
+
+    needle_angle = NumericProperty(0)    
+
     def enable(self):
         self.facade.enable()
         Clock.schedule_interval(self.get_field, 1 / 20.)
+        gps.start(1000, 0)
 
     def disable(self):
         self.facade.disable()
         Clock.unschedule(self.get_field)
 
     def get_field(self, dt):
+        needle_angle = 7
         if self.facade.field != (None, None, None):
             self.x_calib, self.y_calib, self.z_calib = self.facade.field
+            x, y, z = self.facade.field
+
+            needle_angle = Vector(x, y).angle((0, 1)) + 90.
+
+        # fix animation transition around the unit circle
+        if (self.needle_angle % 360) - needle_angle > 180:
+            needle_angle += 360
+        elif (self.needle_angle % 360) - needle_angle < -180:
+            needle_angle -= 360
+        # add the number of revolutions to the result
+        needle_angle += 360 * floor(self.needle_angle / 360.)
+
+        # animate the needle
+        if self._anim:
+            self._anim.stop(self)
+        self._anim = Animation(needle_angle=needle_angle, d=.2, t='out_quad')
+        self._anim.start(self)
 
 
         
@@ -52,6 +76,20 @@ class FlockompassApp(App):
                              Permission.ACCESS_FINE_LOCATION],
                             callback)
 
+    def start(self, minTime, minDistance):
+        gps.start(minTime, minDistance)
+
+    def stop(self):
+        gps.stop()
+
+    def on_pause(self):
+        gps.stop()
+        return True
+
+    def on_resume(self):
+        gps.start(1000, 0)
+
+
     @mainthread
     def on_location(self, **kwargs):
         self.gps_location = '\n'.join([
@@ -78,7 +116,9 @@ class FlockompassApp(App):
 
         root = ScreenManager(transition=RiseInTransition())
         root.add_widget(MapScreen(name='map'))
-        root.add_widget(CompassScreen(name='compass'))
+        cs = CompassScreen(name='compass')
+        cs._anim = None
+        root.add_widget(cs)
 
         return root
 
@@ -96,4 +136,3 @@ if __name__ == '__main__':
         # Button:
         #     text: 'Use RiseInTransition'
         #     on_release: root.manager.transition = RiseInTransition()
-