needle from magnetometer

flockompass.kv

@@ -14,9 +14,9 @@
                     title: 'Social Cycling'
                     with_previous: False
                 ActionButton:
-                    important: True    
+                    important: True
                     text: 'we ride together'
-                    on_press: root.manager.current = 'compass'                    
+                    on_press: root.manager.current = 'compass'
 
         MapView:
             id: mapview
@@ -25,14 +25,15 @@
             zoom: 15
 
             on_map_relocated: centermark.lat = mapview.lat; centermark.lon = mapview.lon
-            
+
             MapMarker:
-                id: centermark    
+                source: 'marker.png'
+                id: centermark
                 anchor_x: 0.2
                 anchor_y: 0.3
                 lat: 28.89335172
                 lon: 76.59449171
-                
+
 
 
 <CompassScreen>:
@@ -73,9 +74,51 @@
                 text: str(root.y_calib) + ','
             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'        
+    #     orientation: 'vertical'
     #     canvas:
     #         Color:
     #             rgb: .98, .98, .98
@@ -86,9 +129,9 @@
     #         source: 'rose.png'
 
     #     Image:
-    #         source: 'needle.png'                    
+    #         source: 'needle.png'
-        
+
-        
+
     #     ActionBar:
     #         pos_hint: {'top':1}
     #         ActionView:
@@ -97,9 +140,9 @@
     #                 title: 'Social Cycling'
     #                 with_previous: False
     #             ActionButton:
-    #                 important: True    
+    #                 important: True
     #                 text: 'set destination'
-    #                 on_press: root.manager.current = 'map' 
+    #                 on_press: root.manager.current = 'map'
 
 
 
@@ -108,4 +151,3 @@
 
     #     Label:
     #         text: app.gps_status
-                    

main.py

@@ -7,33 +7,57 @@ 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):
     hue = NumericProperty(0)
     mapview = MapView(zoom=11, lat=50.6394, lon=3.057)
 
-    
+
 class CompassScreen(Screen):
     hue = NumericProperty(0)
     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)
+
+
+        
 class FlockompassApp(App):
 
     gps_location = StringProperty()
@@ -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([
@@ -60,8 +98,8 @@ class FlockompassApp(App):
     @mainthread
     def on_status(self, stype, status):
         self.gps_status = 'type={}\n{}'.format(stype, status)
-        
+
-    
+
     def build(self):
 
         try:
@@ -75,11 +113,13 @@ class FlockompassApp(App):
         if platform == "android":
             print("gps.py: Android detected. Requesting permissions")
             self.request_android_permissions()
-        
+
         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()
-