GPS Data with iPhone (GPS2IP)

An overview of the utilization of the iPhone for more accurate GPS data

Brandon J. Lacy

Overview

The utilization of GPS data on a robot is a common requirement within projects. However, a majority of hardware components that can be configured with the robot produce lackluster results. The iPhone uses sophisticated technology to produce more accurate GPS data, which makes it a prime candidatee for situation in which a robot is in need of accurate information. The application, GPS2IP, uses the technology of the iPhone and communicates it over the internet. Through this application and the iPhone technology an accurate vehicle to produce GPS data is obtained.

GPS2IP

The application is solely available on iOS. No research was conducted on applications on Android that produce similar functionality. There are two versions of the application on the App Store: GPS2IP ($8.99) and GPS2IP Lite (Free). The free version only allows transmission for 4 minutes before automatically turning off. The paid version has no restrictions.

Walkthrough

iPhone Configuration

Turn Off Auto-Lock

Settings > Display & Brightness > Auto-Lock > Never

GPS2IP Configuration

Enable GPS2IP

Open GPS2IP > Toggle On "Enable GPS2IP" Switch

NMEA Message Type

Open GPS2IP > Settings > NMEA Messages to Send > Only Toggle On "GLL" Switch

Python Code

#!/usr/bin/env python

'''
A module with a GPS node.

GPS2IP: http://www.capsicumdreams.com/gps2ip/
'''

import json
import re
import rospy
import socket

from std_msgs.msg import String

class GPS:
    '''A node which listens to GPS2IP Lite through a socket and publishes a GPS topic.'''
    def __init__(self):
        '''Initialize the publisher and instance variables.'''
        # Instance Variables
        self.HOST = rospy.get_param('~HOST', '172.20.38.175')
        self.PORT = rospy.get_param('~PORT', 11123)

        # Publisher
        self.publisher = rospy.Publisher('/gps', String, queue_size=1)

    def get_coords(self):
        '''A method to receive the GPS coordinates from GPS2IP Lite.'''
        # Instantiate a client object
        with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
            s.connect((self.HOST, self.PORT))
            # The data is received in the RMC data format
            gps_data = s.recv(1024)

        # Transform data into dictionary
        gps_keys = ["message_id", "latitude", "ns_indicator", "longitude", "ew_indicator"]
        gps_values = re.split(',|\*', gps_data.decode())[:5]
        gps_dict = dict(zip(gps_keys, gps_values))

        # Cleanse the coordinate data
        for key in ['latitude', 'longitude']:
            # Identify the presence of a negative number indicator
            neg_num = False

            # The GPS2IP application transmits a negative coordinate with a zero prepended
            if gps_dict[key][0] == '0':
                neg_num = True
            
            # Transform the longitude and latitude into a format that can be utilized by the front-end web-client
            gps_dict[key] = float(gps_dict[key]) / 100

            # Apply the negative if the clause was triggered
            if neg_num:
                gps_dict[key] = -1 * gps_dict[key]

        # Publish the decoded GPS data
        self.publisher.publish(json.dumps(gps_dict))


if __name__ == '__main__':
    # Initialize a ROS node named GPS
    rospy.init_node("gps")

    # Initialize a GPS instance with the HOST and PORT
    gps_node = GPS()

    # Continuously publish coordinated until shut down
    while not rospy.is_shutdown():
        gps_node.get_coords()