Below is the test harness I wrote a couple of weeks ago when I first started using GPSD on one of our products:
#include <stdio.h>
#include <string.h>
#include <stddef.h>
#include <errno.h>
#include <math.h>
#include "/usr/local/include/gps.h"
void main(void)
{
int ret;
struct gps_data_t gps_data;
ret = gps_open("localhost", "2947", &gps_data);
(void)gps_stream(&gps_data, WATCH_ENABLE | WATCH_JSON, NULL);
for (;;) {
/* Put this in a loop with a call to a high resolution sleep () in it. */
if (gps_waiting(&gps_data, 500)) {
errno = 0;
if (gps_read(&gps_data) == -1) {
printf("Read error\n");
exit(1);
} else {
if (gps_data.set) {
printf("\n--- GPS ---\n");
printf("gps_data.online: %10.0f\n", gps_data.online);
printf("gps_data.status: %d\n", gps_data.status);
printf("gps_data.satellites_used: %d\n", gps_data.satellites_used);
printf("gps_data.fix.mode: %d\n", gps_data.fix.mode);
printf("gps_data.fix.time: %10.0f\n", gps_data.fix.time);
printf("gps_data.fix.latitude: %f\n", gps_data.fix.latitude);
printf("gps_data.fix.longitude: %f\n", gps_data.fix.longitude);
printf("gps_data.fix.altitude: %f\n", gps_data.fix.altitude);
printf("gps_data.fix.speed: %f\n", gps_data.fix.speed);
printf("gps_data.fix.track: %f\n", gps_data.fix.track);
printf("gps_data.dop.pdop: %f\n", gps_data.dop.pdop);
}
}
}
}
}
the code is a life from the GPSD documentation and "just works"(tm) for me - YMMV.
Platform is ARM dual-core iMX6; Ubuntu 14.04.5 LTS Server, gcc 5
I'm using GPDS 3.19 built from source and installed in /usr/local/...
My test harness compiles:
cc -o test test.c -l:/usr/local/lib/libgps.so
and runs, thus:
address@hidden:~/vr2200/avld-ng/src/tests$ ./test
--- GPS ---
gps_data.online: 1509705893
gps_data.status: 0
gps_data.satellites_used: 0
gps_data.fix.mode: 0
gps_data.fix.time: nan
gps_data.fix.latitude: nan
gps_data.fix.longitude: nan
gps_data.fix.altitude: nan
gps_data.fix.speed: nan
gps_data.fix.track: nan
gps_data.dop.pdop: nan
--- GPS ---
gps_data.online: 1509705893
gps_data.status: 0
gps_data.satellites_used: 0
gps_data.fix.mode: 0
gps_data.fix.time: nan
gps_data.fix.latitude: nan
gps_data.fix.longitude: nan
gps_data.fix.altitude: nan
gps_data.fix.speed: nan
gps_data.fix.track: nan
gps_data.dop.pdop: nan
--- GPS ---
gps_data.online: 1509705893
gps_data.status: 0
gps_data.satellites_used: 0
gps_data.fix.mode: 0
gps_data.fix.time: nan
gps_data.fix.latitude: nan
gps_data.fix.longitude: nan
gps_data.fix.altitude: nan
gps_data.fix.speed: nan
gps_data.fix.track: nan
gps_data.dop.pdop: nan
--- GPS ---
gps_data.online: 1509705894
gps_data.status: 1
gps_data.satellites_used: 0
gps_data.fix.mode: 3
gps_data.fix.time: 1509705894
gps_data.fix.latitude: 52.230025
gps_data.fix.longitude: -2.188018
gps_data.fix.altitude: 43.450000
gps_data.fix.speed: 0.043000
gps_data.fix.track: 280.369300
gps_data.dop.pdop: nan
--- GPS ---
gps_data.online: 1509705895
gps_data.status: 1
gps_data.satellites_used: 0
gps_data.fix.mode: 3
gps_data.fix.time: 1509705895
gps_data.fix.latitude: 52.230026
gps_data.fix.longitude: -2.188018
gps_data.fix.altitude: 43.468000
gps_data.fix.speed: 0.040000
gps_data.fix.track: 307.944700
gps_data.dop.pdop: nan
--- GPS ---
gps_data.online: 1509705896
gps_data.status: 1
gps_data.satellites_used: 0
gps_data.fix.mode: 3
gps_data.fix.time: 1509705896
gps_data.fix.latitude: 52.230026
gps_data.fix.longitude: -2.188017
gps_data.fix.altitude: 43.568000
gps_data.fix.speed: 0.017000
gps_data.fix.track: 1.317500
gps_data.dop.pdop: nan
--- GPS ---
gps_data.online: 1509705896
gps_data.status: 1
gps_data.satellites_used: 14
gps_data.fix.mode: 3
gps_data.fix.time: 1509705896
gps_data.fix.latitude: 52.230026
gps_data.fix.longitude: -2.188017
gps_data.fix.altitude: 43.568000
gps_data.fix.speed: 0.017000
gps_data.fix.track: 1.317500
gps_data.dop.pdop: 1.380000
--- GPS ---
gps_data.online: 1509705897
gps_data.status: 1
gps_data.satellites_used: 14
gps_data.fix.mode: 3
gps_data.fix.time: 1509705897
gps_data.fix.latitude: 52.230026
gps_data.fix.longitude: -2.188016
gps_data.fix.altitude: 43.645000
gps_data.fix.speed: 0.030000
gps_data.fix.track: 43.908300
gps_data.dop.pdop: 1.380000
--- GPS ---
gps_data.online: 1509705898
gps_data.status: 1
gps_data.satellites_used: 14
gps_data.fix.mode: 3
gps_data.fix.time: 1509705898
gps_data.fix.latitude: 52.230026
gps_data.fix.longitude: -2.188016
gps_data.fix.altitude: 43.603000
gps_data.fix.speed: 0.008000
gps_data.fix.track: 177.232800
gps_data.dop.pdop: 1.380000
Hope this helps.
Regards
Mike
On 11/3/2017 5:10 AM, David Huichen Dai
wrote:
Hi all,
I have gpsd and libgps installed on my Ubuntu 14.04 using the apt-get install command. The gpsd version is 3.9 (Ubuntu software center does not have gpsd updated to the latest version).
I use the following code (from stackoverflow) to get the coordinates (latitude and longitude). This code uses socket to communicate with the gpsd daemon process, generally it works well.But I often find that the gps_waiting function returns false, and after that even I re-run this code, the coordinates can no longer be obtained (still fail at gps_waiting). I tried several methods, like killing the gpsd process and restart it, removing the /var/run/gpsd.sock, all didn't work. The only thing I can do is to reboot the computer. I have got two questions:
1. How to avoid this problem.2. This is only a toy program. In my project, I need to have the latest coordinates immediately whenever I want, I dont want to wait for any time before I can have the coordinates, also not in a loop as in this toy program. How could I achieve this?
I am very happy to see some sample code in real projects. Your help are very much appreciated. Thank you!
Best wishes,David
#include <gps.h> #include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <math.h> int main() { int rc; struct timeval tv; struct gps_data_t gps_data; if ((rc = gps_open("localhost", "2947", &gps_data)) == -1) { printf("code: %d, reason: %s\n", rc, gps_errstr(rc)); return EXIT_FAILURE; } gps_stream(&gps_data, WATCH_ENABLE | WATCH_JSON, NULL); while (1) { /* wait for 2 seconds to receive data */ if (gps_waiting (&gps_data, 2000000)) { /* read data */ if ((rc = gps_read(&gps_data)) == -1) { printf("error occured reading gps data. code: %d, reason: %s\n", rc, gps_errstr(rc)); } else { /* Display data from the GPS receiver. */ if ((gps_data.status == STATUS_FIX) && (gps_data.fix.mode == MODE_2D || gps_data.fix.mode == MODE_3D) && !isnan(gps_data.fix.latitude) && !isnan(gps_data.fix.longitude)) { //gettimeofday(&tv, NULL); EDIT: tv.tv_sec isn't actually the timestamp! printf("latitude: %f, longitude: %f, speed: %f, timestamp: %ld\n", gps_data.fix.latitude, gps_data.fix.longitude, gps_data.fix.speed, gps_data.fix.time); //EDIT: Replaced tv.tv_sec with gps_data.fix.time } else { printf("no GPS data available\n"); } } } else printf("waiting failed.\n"); } /* When you are done... */ gps_stream(&gps_data, WATCH_DISABLE, NULL); gps_close (&gps_data); return EXIT_SUCCESS; }
--
==================================================
David Huichen Dai, PhDResearch assistant
Lab of Broadband Network Switching Technology and Communication
Dept. of Computer Science and Technology
Tsinghua University, Beijing, P.R. China, 100084
Tel: 86-010-6277-3441
Email: address@hidden; address@hidden
==================================================
--
Michael
J Tubby B.Sc MIET / Technical Director
address@hidden / +44 (0)7973 225144
Thorcom
Systems Ltd
Office: +44 (0)1905 756 700
/ Fax: +44 (0)1905 755 777
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Blackpole Trading Estate West, Worcester, WR3 8TJ Registered in England
& Wales 2704696 / VAT number GB 487 9256 81
www.thorcom.co.uk