def waitForInitialState( self ):
        '''Before a command has been sent we wait for an observation of the world and a frame.'''
        # wait for a valid observation
        world_state = self.agent_host.peekWorldState()
        while world_state.is_mission_running and all(e.text=='{}' for e in world_state.observations):
            world_state = self.agent_host.peekWorldState()
        # wait for a frame to arrive after that
        num_frames_seen = world_state.number_of_video_frames_since_last_state
        while world_state.is_mission_running and world_state.number_of_video_frames_since_last_state == num_frames_seen:
            world_state = self.agent_host.peekWorldState()
        world_state = self.agent_host.getWorldState()

        if world_state.is_mission_running:
                
            assert len(world_state.video_frames) > 0, 'No video frames!?'
            
            obs = json.loads( world_state.observations[-1].text )
            self.prev_x   = obs[u'XPos']
            self.prev_y   = obs[u'YPos']
            self.prev_z   = obs[u'ZPos']
            self.prev_yaw = obs[u'Yaw']
            print('Initial position:',self.prev_x,',',self.prev_y,',',self.prev_z,'yaw',self.prev_yaw)
            
            if save_images:
                # save the frame, for debugging
                frame = world_state.video_frames[-1]
                image = Image.frombytes('RGB', (frame.width, frame.height), bytes(frame.pixels) )
                self.iFrame = 0
                self.rep = self.rep + 1
                image.save( 'rep_' + str(self.rep).zfill(3) + '_saved_frame_' + str(self.iFrame).zfill(4) + '.png' )
            
        return world_state
Before a command has been sent we wait for an observation of the world and a frame.