View source for HowTo Setup The NST System With A GPS (gpsd)

= Why Connect A GPS? =

The primary reason you would connect a GPS to a NST system is to geolocate systems based on WIFI transmissions.

* You connect a GPS to your NST system.
* You run the '''kismet''' process which will scan for systems using WIFI communications.
* You then view the locations of discovered WIFI systems in Google Earth.

This page provides information on getting a GPS properly connected to a NST system. For details on using '''kismet''' after you have your GPS connected, see: "[[HowTo Geolocate kismet Data]]".

= Selecting GPS Hardware =

It can be tricky in selecting GPS hardware that will be compatible with your NST system. Basically, you want to look for:

* GPS hardware which can put out the NMEA data such as the v2.1 GSA format.
* The necessary hardware and drivers to physically connect the GPS hardware to your NST system.

The [http://gpsd.berlios.de/hardware.html Compatible GPSes] list at the [http://gpsd.berlios.de/|gpsd web site] is probably a good place to start. However, GPS models change so frequently, you may find yourself searching for reader comments and feedback at on-line stores.

Here is a photo of a Magellan Meridian Color GPS with its RS-232 adapter and a serial to USB adapter which are known to work:

[[File:magellan-meridan-color.jpg|center|frame|Magellan Meridian Color GPS and serial to USB adapter]]

Unfortunately, the serial to USB adapter was purchased a long time ago (probably from http://www.cyberguys.com/). The only labeling on the serial to USB adapter shown above is a model number of ''GUC232''.


= Testing GPS Connection =

== Connecting a Serial GPS ==

Connecting and configuring your GPS hardware will vary based on your situation. The photo below shows a ASUS Eeee PC running NST v2.13.0. The Magellan Meridian Color GPS is then plugged into a serial to USB adapter which is then plugged into the ASUS Eeee PC.

[[File:asus-gps.jpg|center|frame|Magellan Meridian Color GPS and serial to USB adapter connected to a ASUS Eeee PC]]

== Configuring the GPS ==

You will need to configure your GPS device such that it sends data to your NST system. For the ''Magellan Meridian Color'' GPS, I needed to go through the setup panel, locate the ''NMEA'' menu and enable the ''v2.1 GSA'' output.

== Listing Serial Devices ==

The following command is useful in quickly showing what serial devices have been identified by the NST system:

 [root@cayenne ~]# ls -l /dev/tty*S*
 crw-rw---- 1 root dialout   4, 64 Sep 21 13:12 /dev/ttyS0
 crw-rw---- 1 root dialout   4, 65 Sep 21 13:12 /dev/ttyS1
 crw-rw---- 1 root dialout   4, 66 Sep 21 13:12 /dev/ttyS2
 crw-rw---- 1 root dialout   4, 67 Sep 21 13:12 /dev/ttyS3
 crw-rw---- 1 root dialout 188,  0 Sep 22 16:43 /dev/ttyUSB0
 [root@cayenne ~]# 

The ''/dev/ttyUSB0'' adapter entry tells me that there is only one serial to USB adapter plugged into the system. The other entries (''/dev/ttyS0'' - ''/dev/ttyS3'') indicate standard serial port entries. However, the ASUS Eeee PC does not have any physical serial ports which the GPS can be connected to, so I know that these serial entries are not being used by my GPS.

== Using '''gtkterm''' to View GPS Data ==

You can use the '''gtkterm''' utility to verify that the GPS is sending data to the NST system. You can launch this utility from the command line as shown below (you will need to run this as ''root'' or a user which belongs to the ''dialout'' group):

 [root@cayenne ~]# gtkterm &
 [root@cayenne ~]#

After launching the '''gtkterm''' application, you will need to open up the ''Configuration'' menu and specify the port settings. Again, this will vary based on your GPS. In the situation shown in the image below, the serial connection was set to 9600 baud, 8 data bits, no parity, and 1 stop bit. If 9600 baud doesn't work for you, try 4800 baud or check the settings of your GPS.

[[File:gtkterm-gps-nmea-data.png|center|frame|Using gtkterm to display data from a GPS]]

= Setting Up '''gpsd''' =

Once you've completed the above steps and know that your GPS is sending data to your NST system, you can then setup the [http://gpsd.berlios.de/|gpsd] daemon. The '''gpsd''' service is used to provide location information to other processes (like '''kismet''').

== Editing: ''/etc/sysconfig/gpsd'' ==

The first step in setting up the '''gpsd''' service is to edit its configuration file. Most likely you will only need to change the serial device which your GPS is connected to.

Here is the configuration I use for the Magellan Meridian Color GPS and serial to USB adapter hardware which I have:

<pre class="programlisting">
OPTIONS="-n"
DEVICE="/dev/ttyUSB0"
</pre>

See the man page for the '''gpsd''' process for additional configuration options.

== Starting The '''gpsd''' Service ==

Once you've updated the '''gpsd''' configuration file, you can start the '''gpsd''' service using the following command:

 [root@cayenne ~]# service gpsd start
 Starting gpsd:                                             [  OK  ]
 [root@cayenne ~]# 

= Testing '''gpsd''' Configuration =

After starting the '''gpsd''' service, you should verify that it is functioning.

== Using '''lsof''' ==

You can use the '''lsof''' command to make sure that the '''gpsd''' command is listening for TCP connections. For example:

 [root@cayenne ~]# lsof -i :2947
 COMMAND  PID   USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
 gpsd    3501 nobody    4u  IPv4 213907      0t0  TCP localhost.localdomain:gpsd (LISTEN)
 [root@cayenne ~]# 

The output above tells us that the '''gpsd''' process is listening for connections on port ''2947''. It should also be noted that it is only accepting connections from the localhost (127.0.0.1).


== Using '''telnet''' ==

We can '''telnet''' to the '''gpsd''' service and press the ''o'' key several times to get some information back from the '''gpsd''' service. To exit from the '''telnet''' connection, we will press ''Control-['' and then enter the word ''close''.

 [root@cayenne ~]# telnet 127.0.0.1 2947
 Trying 127.0.0.1...
 Connected to 127.0.0.1.
 Escape character is '^]'.
 GPSD
 GPSD,O=?
 GPSD,O=GSV 1285257413.870 0.005 39.953486667 -86.112073333 254.000 36.000 20.700 0.0000 0.000 0.000 ? 24001.74 ? 3
 GPSD,O=GSV 1285257415.850 0.005 39.953486667 -86.112073333 254.000 31.500 18.975 0.0000 0.000 0.000 ? 64.09 ? 3
 
 telnet> close
 Connection closed.
 [root@cayenne ~]# 


== Using ''xgps'' ==

You can use the ''xgps'' command to bring up a graphical interface to the '''gpsd''' service. Running:

 [root@cayenne ~]# xgps &
 [root@cayenne ~]# 

The '''xgps''' utility shows a lot of the information provided by the '''gpsd''' service. For example, in the image below, you can see what satellites were used by the GPS in forming a solution and the current location of the GPS.

[[File:xgps-check-gpsd.png|center|frame|Using xgps to show GPS information provided by the gpsd service]]