Re: [gpsd-users] gpsd WATCH_RAW

[Roger Oberholtzer]

I have made a little test program that is reading from gpsd (started with 
gpsfake).


#include <stdio.h>
#include <gps.h>

main() {

        struct gps_data_t gpsdata;

        gps_open("localhost", DEFAULT_GPSD_PORT, &gpsdata);

        (void) gps_stream(&gpsdata, WATCH_ENABLE | WATCH_RAW, NULL);

        while (1) {

                if (gps_waiting (&gpsdata, 500)) {

                        if (gps_read (&gpsdata) == -1) {
                                // ...
                        } else {
                                printf("%s\n", gps_data(&gpsdata));
                        }
                }
        }

        (void) gps_stream(&gpsdata, WATCH_DISABLE, NULL);
        (void) gps_close (&gpsdata);

}


Why would gps_data() return some JSON headers at the start? I get this:

{"class":"VERSION","release":"3.10","rev":"3.10","proto_major":3,"proto_minor":9}
{"class":"WATCH","enable":true,"json":false,"nmea":false,"raw":2,"scaled":false,"timing":false,"split24":false,"pps":false}
","flags":1,"native":0,"bps":4800,"parity":"N","stopbits":1,"cycle":1.00}]}
{"class":"WATCH","enable":true,"json":false,"nmea":false,"raw":2,"scaled":false,"timing":false,"split24":false,"pps":false}
$GPGGA,094857.50,5055.59050842,N,00701.48761436,E,2,05,2.5,45.275,M,47.654,M,22.7,0100*4B
$GPGGA,094857.60,5055.58953121,N,00701.48716086,E,2,05,2.5,45.347,M,47.654,M,22.8,0100*4F
$GPGGA,094857.70,5055.58857263,N,00701.48667388,E,2,05,2.5,45.374,M,47.654,M,22.9,0100*45
$GPGGA,094857.80,5055.58760440,N,00701.48619977,E,2,05,2.5,45.401,M,47.654,M,23.0,0100*48
$GPGGA,094857.90,5055.58664631,N,00701.48571662,E,2,05,2.5,45.423,M,47.654,M,23.1,0100*4F


The GGA stuff is ok. The JSON is a mystery. Perhaps there is a flag in the 
gps_read() that tells the type of data so I can skip other than the real NMEA 
strings? But when I only said I wanted RAW, should I expect other stuff as 
well? Also, the JSON strings are always reported as shown here. The third line 
looks odd.

If I choose WATCH_JSON, I also get these strings at the start. But as they are 
JSON this seems less mysterious. Also, the third line looks odd here as well:

{"class":"VERSION","release":"3.10","rev":"3.10","proto_major":3,"proto_minor":9}
{"class":"WATCH","enable":true,"json":true,"nmea":false,"raw":0,"scaled":false,"timing":false,"split24":false,"pps":false}
Z","flags":1,"native":0,"bps":4800,"parity":"N","stopbits":1,"cycle":1.00}]}
{"class":"WATCH","enable":true,"json":true,"nmea":false,"raw":0,"scaled":false,"timing":false,"split24":false,"pps":false}
{"class":"TPV","tag":"GGA","device":"/dev/pts/7","mode":3,"time":"2009-04-01T09:49:28.200Z","ept":0.005,"lat":50.922154551,"lon":7.021976050,"alt":44.252,"speed":1049.000,"climb":-1.047}
{"class":"TPV","tag":"GGA","device":"/dev/pts/7","mode":3,"time":"2009-04-01T09:49:28.300Z","ept":0.005,"lat":50.922149416,"lon":7.021953345,"alt":44.250,"speed":16.956,"climb":-0.020}
{"class":"TPV","tag":"GGA","device":"/dev/pts/7","mode":3,"time":"2009-04-01T09:49:28.400Z","ept":0.005,"lat":50.922144627,"lon":7.021930506,"alt":44.248,"speed":16.920,"climb":-0.020}
{"class":"TPV","tag":"GGA","device":"/dev/pts/7","mode":3,"time":"2009-04-01T09:49:28.500Z","ept":0.005,"lat":50.922139731,"lon":7.021907576,"alt":44.246,"speed":17.018,"climb":-0.020}
{"class":"TPV","tag":"GGA","device":"/dev/pts/7","mode":3,"time":"2009-04-01T09:49:28.600Z","ept":0.005,"lat":50.922135037,"lon":7.021884639,"alt":44.245,"speed":16.953,"climb":-0.010}


Am I missing the docs for this? The libgps man page does not seem to have much 
to say about this access method.


Roger Oberholtzer

Ramböll RST

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