Derwynd's Weblog

GPS on Linux

Compile kernel with usb-modem feature

Connect the GPS to usb port ….

Check /var/log/messages

$ tailf /var/log/messages

Jun 20 22:26:39 localhost kernel: usb 6-2: new full speed USB device using uhci_hcd and address 3
Jun 20 22:26:40 localhost kernel: usb 6-2: configuration #1 chosen from 1 choice
Jun 20 22:26:40 localhost kernel: cdc_acm 6-2:1.0: ttyACM0: USB ACM device

Device created is ttyACM0

This should give you a continuous stream

$ cat /dev/ttyACM0

$GPRMC,071601.00,A,1907.09660,N,07252.30735,E,0.029,235.62,130711,,,A*67
$GPGGA,071601.00,1907.09660,N,07252.30735,E,1,09,2.21,33.2,M,-62.8,M,,*40
$GPGSV,3,1,12,13,82,086,34,20,11,177,35,19,43,072,35,10,25,274,*77
$GPGSV,3,3,12,07,40,343,15,11,20,137,31,08,25,316,10,28,32,250,*7A
$GPZDA,071601.00,13,07,2011,00,00*60

Now that the device is detected lets install the rpms required

$ yum install -y gpsd gpsd-clients

Incase Not created Please create

Created startup script

$ cat /etc/init.d/gpsd
#!/bin/sh
#
# gpsd Service daemon for mediating access to a GPS
#
# chkconfig: – 44 66
# description: gpsd is a service daemon that mediates access to a GPS sensor \
# connected to the host computer by serial or USB interface, \
# making its data on the location/course/velocity of the sensor \
# available to be queried on TCP port 2947 of the host computer.
# processname: gpsd
# pidfile: /var/run/gpsd.pid

case “$1″ in
start|stop|restart)
$1
;;
force-reload)
restart
;;
status)
status $prog
;;
try-restart|condrestart)
if status $prog >/dev/null ; then
restart
fi
;;
reload)
status $prog >/dev/null || exit 7
# If config can be reloaded without restarting, implement it here,
# remove the “exit”, and add “reload” to the usage message below.
action $”Service $prog does not support the reload action: ” /bin/false
exit 3
;;
*)
echo $”Usage: $0 {start|stop|status|restart|try-restart|force-reload}”
exit 2
esac

$ echo “/etc/init.d/gpsd start ” >> /etc/rc.local
Or start it via services

Graphic front end
$ /usr/bin/xgps

Running cgps utility, I can obtain the following (You will know where I am by interpreting the Lat/Lon). cgps runs on serial or console terminal and connects to local port 2947, which is the default port that gpsd listened to for serving queries from client programs:

$ cgps localhost 2947

CGPS Test Client
┌───────────────────────────────────────────┐┌─────────────────────────────────┐
│ Time: 2011-07-13T06:27:43.00Z ││PRN: Elev: Azim: SNR: Used: │
│ Latitude: 19.118427 N ││ │
│ Longitude: 72.871813 E ││ │
│ Altitude: 50.3 m ││ │
│ Speed: 0.0 kph ││ │
│ Heading: 356.4 degrees ││ │
│ HPE: 8 m ││ │
│ VPE: 13 m ││ │
│ Climb: 0.0 m/min ││ │
│ Status: 3D FIX ││ │
│ Change: 0 secs ││ │
│ ││ │
│ ││ │
└───────────────────────────────────────────┘└─────────────────────────────────┘
┌───────────────────────────────────────────┐
│Command: │
└───────────────────────────────────────────┘
GPSD,O=GGA 1310538463.00 0.005 19.118427 72.871813 50.30 ? ? 356
.4500 0.011 0.000 ? ? ?
GPSD,O=GSA 1310538463.00 0.005 19.118427 72.871813 50.30 8.32 13.20 356.4500
0.011 0.000 165.6961 16.64 ?

There are two more native way to interact with gpsd for retrieving GPS data – by telnet or gpspipe. Since gpsd listen to port 2947, you can just “telnet” to it. Once connect, type ‘p’ or ‘d’ followed by return will query for position and time respectively

$ telnet localhost 2947
Trying 127.0.0.1…
Connected to localhost.
Escape character is ‘^]’.
p
GPSD,P=19.118280 72.871878
d
GPSD,D=2011-07-13T06:33:19.00Z

$ gpspipe -r localhost 2947
GPSD,R=1
$GPGSV,4,2,14,10,25,287,14,32,05,165,,06,16,048,33,23,63,124,48*70
$GPGSV,4,3,14,03,29,054,35,07,36,330,,16,08,039,,08,20,305,29*74
$GPGSV,4,4,14,11,15,147,,28,25,239,26*7B
$GPGLL,1907.09502,N,07252.31343,E,065047.00,A,A*6C
$GPZDA,065047.00,13,07,2011,00,00*61

Setting up time via gps

#!/bin/bash
#setup time via gps
i=0;
while [ "$i" -lt 5 ];
do
sleep 5
(echo d ; sleep 1; echo d; sleep 1; echo d) | (nc localhost 2947) > /tmp/gps_time &
TEST=$!
sleep 4
kill -s SIGINT $TEST
i=$(($i+1))
date=$`cat /tmp/gps_time | tail -n 1`
year=$(echo $date | sed ‘s/.*D=\([0-9]*\)-.*/\1/’)
[ "$year" -gt 2004 ] && break
done;
echo “slept $i times while waiting gps lock..”

echo “Setting date $date”
export TZ=UTC
date $(echo $date | sed ‘s/GPSD,D=\([0-9]*\)\(.*\):.*/\2\1/’ | sed ‘s/[^0-9]//g’)
sleep 2
export TZ=”/usr/share/zoneinfo/Asia/Calcutta”
add3sec=`date –date=’3 seconds’`
date -s “${add3sec}”
date
hwclock –systohc
hwclock

Getting Location via bash
#!/bin/bash
#setup time via gps
i=0;
while [ "$i" -lt 5 ];
do
sleep 5
(echo dp ) | (nc localhost 2947) > /tmp/gps_location &
TEST=$!
sleep 1
kill -s SIGINT $TEST
i=$(($i+1))
echo $i
done;
echo “slept $i times while waiting gps lock..”

cat /tmp/gps_location| \
awk -F “P=” ‘{ print $NF}’ | \
awk ‘{ print “Latitude: ” $1 ” Longitude: ” $2}’

July 17, 2011 - Posted by derwynd | Uncategorized