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sdk:gps-udp-client-gnsstogps [2019/07/08 13:56] – fachetsdk:gps-udp-client-gnsstogps [2021/10/08 10:22] (current) – [SDK Script gps-udp-client-GNSStoGPS.are] dodenhoeft
Line 1: Line 1:
 +====== Background ======
 +GPS was the first Global Navigation Satellite System (GNSS) and the term GPS is often used as a synonym for GNSS.
 +
 +Older software often only checks for NMEA 0183 sentences starting with <nowiki>"$GP"</nowiki> (= GPS only) instead of looking for  all GNSS systems.
 +
 +Newer GNSS receivers often use multiple GNSS systems and therefore <nowiki>"$GN"</nowiki> is used (<nowiki>"$GNRMC..."</nowiki>) if it recives a combination of GPS, Galileo and GLONASS signals.
 +
 +It would be better to us instead of <nowiki>"$GPRMC"</nowiki> either <nowiki>"$G.RMC"</nowiki> ("." = anychar) for using GPS, Galileo and/or GLONASS (GNSS) or even <nowiki>"$..RMC"</nowiki> which means any source.
 +
 +<code>
 +NMEA 0183 sentence "$XXYYY..." explanation:
 +
 +"$" = Start 
 +"XX" = Source device (https://de.wikipedia.org/wiki/NMEA_0183#Ger%C3%A4te-IDs)
 + BD = Beidu
 + GA = Galileo
 + GL = GLONASS
 + GP = GPS
 + GN = GNSS position fix from more than one constellation (eg. GPS + GLONASS)
 +"YYY" = Record
 + RMC = Recommended Minimum Sentence C (used in most cases)
 + GGA = Global Positioning System Fix Data
 + GNS = GNSS fixed data
 + GLL = Geographic Position - Latitude/Longitude
 + ...
 +
 +Source: https://de.wikipedia.org/wiki/NMEA_0183
 +</code>
 +
 ====== SDK Script gps-udp-client-GNSStoGPS.are ====== ====== SDK Script gps-udp-client-GNSStoGPS.are ======
 +<code c gps-udp-client-gnsstogps.are>
 /* DESC: This script sends the local GPS NMEA stream to a remote UDP server. /* DESC: This script sends the local GPS NMEA stream to a remote UDP server.
 * DESC: It checks for the correct CR/LF end of line characters and convert messages $GN to $GP  * DESC: It checks for the correct CR/LF end of line characters and convert messages $GN to $GP 
Line 22: Line 52:
  
  nb_config_set("gpsd.0.status=0");  nb_config_set("gpsd.0.status=0");
- sleep(3);+                do { 
 +                                sleep(3); 
 +                } while ( nb_config_done() != 0) 
 +     
  nb_config_set("gpsd.0.status=1");  nb_config_set("gpsd.0.status=1");
- sleep(5); +                do { 
 +                 sleep(5); 
 +                } while ( nb_config_done() != 0)
  return 0;  return 0;
 } }
- 
 int gpsd_connect () int gpsd_connect ()
 { {
Line 38: Line 71:
  exit(-1);  exit(-1);
  }  }
- for (attempt = 0; attempt <= 5; attempt++) { + for (attempt = 0; attempt <= 15; attempt++) { 
- sleep(3);+ sleep(15);
  
  if (connect(gpsd, local_ip, local_port) < 0) {  if (connect(gpsd, local_ip, local_port) < 0) {
  nb_syslog("Could not connect to daemon");  nb_syslog("Could not connect to daemon");
- if (attempt == 3) {+ if (attempt == 12) {
  nb_syslog("Unable to connect, restarting daemon");  nb_syslog("Unable to connect, restarting daemon");
  gpsd_restart();  gpsd_restart();
Line 52: Line 85:
  }  }
  nb_syslog("Connected to daemon, requesting NMEA");  nb_syslog("Connected to daemon, requesting NMEA");
- send(gpsd,"R=1\n");+ send(gpsd, "R=1\n");
  
  nb_syslog("Processing NMEA");  nb_syslog("Processing NMEA");
  
  return gpsd;  return gpsd;
 +}
 +
 +string checksum(string s)
 +{
 + pos = strchr(s, "*");
 +
 +  if (is_void(pos))
 + return s; /* no checksum to correct */
 +
 + cs = 0;
 + chars = explode(s);
 +        for (i = 1; i < pos; i++) { /* skip $ and *XX */ 
 +     c = ord(chars[i]);
 +            cs ^= c;
 +        }
 +        r = sprintf("%s%02X%s", substr(s, 0, pos + 1), cs, substr(s, pos + 3));
 + return r;
 } }
  
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 /* open UDP server socket */ /* open UDP server socket */
 server = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP); server = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
-if(server < 0) {+if (server < 0) {
  nb_syslog("Unable to open socket");  nb_syslog("Unable to open socket");
  exit(-1);  exit(-1);
Line 104: Line 154:
  data = recv(gpsd);  data = recv(gpsd);
  len = strlen(data);  len = strlen(data);
- printf("received %d\n", len); 
  /* Check for correct framing: CR+LF */  /* Check for correct framing: CR+LF */
  if(len > 2) {  if(len > 2) {
Line 123: Line 172:
  }  }
  /* Convert message $GN to $GP for backward compatibility */  /* Convert message $GN to $GP for backward compatibility */
- printf("vor %s\n", data); 
  if(strstr(data, "$GN") == 0) {;  if(strstr(data, "$GN") == 0) {;
  a_arr = explode(data);  a_arr = explode(data);
  a_arr[2] = "P";  a_arr[2] = "P";
- data = implode(a_arr);+ data = checksum(implode(a_arr));
  }  }
- printf("nach %s\n", data); 
  /* skip all messages different from GPGGA   /* skip all messages different from GPGGA 
  * if(strstr(data,"$GPGGA")==())  * if(strstr(data,"$GPGGA")==())

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sdk/gps-udp-client-gnsstogps.1562594218.txt.gz · Last modified: 2019/07/08 13:56 by fachet