map: add altitude information to click data

MAVProxy/modules/mavproxy_map/mp_slipmap_ui.py

@@ -353,6 +353,8 @@ def __init__(self, parent, state):
         self.mouse_down = None
         self.click_pos = None
         self.last_click_pos = None
+        self.last_click_pos_used_for_text = None
+        self.last_terrain_height = None
         if state.elevation != "None":
             state.ElevationMap = mp_elevation.ElevationModel(database=state.elevation)
 
@@ -486,21 +488,56 @@ def update_position(self):
         if alt == -1:
             newtext += ' SRTM Downloading '
         newtext += '\n'
-        if self.click_pos is not None:
-            newtext += 'Click: %.8f %.8f (%s %s) (%s)' % (self.click_pos[0], self.click_pos[1],
-                                                      mp_util.degrees_to_dms(self.click_pos[0]),
-                                                      mp_util.degrees_to_dms(self.click_pos[1]),
-                                                      mp_util.latlon_to_grid(self.click_pos))
+
+        self.update_click_position_text()
+
+    def update_click_position_text(self):
+        if self.click_pos is None:
+            return
+        if self.click_pos == self.last_click_pos:
+            return
+
+        if self.click_pos == self.last_click_pos_used_for_text:
+            return
+
+        terrain_height = None
+        terrain_height_str = "?"
+        if self.state.elevation != "None":
+            terrain_height = self.state.ElevationMap.GetElevation(self.click_pos[0], self.click_pos[1])
+            if terrain_height is not None:
+                terrain_height_str = ' %.1fm' % (terrain_height,)
+
+        newtext = 'Click: %.8f %.8f %s (%s %s) (%s)' % (
+            self.click_pos[0],
+            self.click_pos[1],
+            terrain_height_str,
+            mp_util.degrees_to_dms(self.click_pos[0]),
+            mp_util.degrees_to_dms(self.click_pos[1]),
+            mp_util.latlon_to_grid(self.click_pos)
+        )
+
         if self.last_click_pos is not None:
+            # provide information about the differences between the
+            # previous click position:
             distance = mp_util.gps_distance(self.last_click_pos[0], self.last_click_pos[1],
                                             self.click_pos[0], self.click_pos[1])
             bearing = mp_util.gps_bearing(self.last_click_pos[0], self.last_click_pos[1],
                                             self.click_pos[0], self.click_pos[1])
             newtext += '  Distance: %.3fm %.3fnm Bearing %.1f' % (distance, distance*0.000539957, bearing)
-        if newtext != state.oldtext:
+            if terrain_height == "?":
+                self.last_terrain_height = None
+            else:
+                if self.last_terrain_height is not None:
+                    delta = terrain_height - self.last_terrain_height
+                    newtext += " (height %f)" % (delta, )
+        self.last_terrain_height = terrain_height
+
+        if newtext != self.state.oldtext:
             self.position.Clear()
             self.position.WriteText(newtext)
-            state.oldtext = newtext
+            self.state.oldtext = newtext
+
+        self.last_click_pos_used_for_text = self.click_pos
 
     def pixel_coords(self, latlon, reverse=False):
         '''return pixel coordinates in the map image for a (lat,lon)