GPS Parser

##GPS Parser Processing Class

Using the serial port wrapper (as Bluetooth supports serial port emulation [BlueTooth Serial Port Profile]), it is very fast and easy to parse bluetooth gps devices. GPS sensors actually have some specification for their output called NMEA. Only a subset of it was implemented, the GPRMC part to be precise. This is some formatted text only output looking for example like

"$GPRMC,081836,A,3751.65,S,14507.36,E,000.0,360.0,130998,011.3,E*62"

which has to be converted to Google maps coordinates.

The GPS sensor was developed using a GPSlim device but should be successfully used by any device following the NMEA specification. It was actually tested with a Nokia GPS device without any modification. The only small problem was the linkage of the Nokia GPS device which requires a passcode. It can be found deep down in the documentation and is 0000 by default.

###Connecting a GPS device to gpsd GPSD is a Linux daemon that monitors one or more GPS devices attached to a host computer through serial or USB ports. All data of the GPS devices is made available to be queried on TCP port 2947 of the host computer. With gpsd, multiple GPS client applications (such as navigational and wardriving software) can share access to GPS devices without contention or loss of data. Also, gpsd responds to queries with a format that is substantially easier to parse than the NMEA 0183 emitted by most GPS devices.

Supported by GPSD:

• NMEA 0183 protocol
• Rockwell binary protocol
• TSIP binary protocol
• SiRF protocol
• Garmin binary protocol
• Evermore binary protocol

###Using Bluetooth We are given a Bluetooth GPS device that we want to connect to a Linux host. In this tutorial, it's a HOLUX GPSlim 236.

• First, we need to start bluetooth services:

sudo /etc/init.d/bluetooth start

Now, let's scan for bluetooth devices:

hcitool scan

This should return a list of devices like

00:0B:0D:85:77:79 HOLUX GPSlim236
00:16:4E:D7:AE:5F Nokia N70
00:12:62:AF:C0:6E Nino
00:11:67:80:41:96 BT-GPS

As already mentioned, we are going to use the HOLUX GPSlim 236. We want to map the HOLUX GPSlim 236 to a emulated RS-232 serial port. To this end, we use the Bluetooth protocol RFCOMM. That's pretty simple and goes as follows. First we create a config file for the RFCOMM:

sudo nano /etc/bluetooth/rfcomm.conf

and add an entry for our HOLUX GPSlim 236 to this file

rfcomm0 {
	bind yes;
	device '00:0B:0D:85:77:79';
	channel 1;
	comment "Your comment here";
}

This way, we are mapping the HOLUX to a emulated RS-232 serial port

/dev/rfcomm0

by using the shell command

sudo rfcomm connect 0

We should get the following return

Connected /dev/rfcomm0 to 00:0B:0D:85:77:79 on channel 1
Press CTRL-C for hangup

Great, now we open a second terminal and connect the gpsd to our /dev/rfcomm0

sudo gpsd -b -N -D 4 /dev/rfcomm0

You can telnet into the gpsd to play around and check if it's working correctly

telnet localhost 2947

Cool, now we have a Bluetooth GPS device connected to a Linux host! A GSN server can use it to read the GPS data.