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sdk:gps-udp-client-gnsstogps [2019/07/08 14:13] fachet |
sdk:gps-udp-client-gnsstogps [2019/11/28 11:23] fachet |
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+ | ====== 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(multiple GNSS sources) | ||
+ | "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> | <code c gps-udp-client-gnsstogps.are> | ||
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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; | ||
} | } | ||
Line 126: | Line 172: | ||
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)); |
} | } | ||
/* skip all messages different from GPGGA | /* skip all messages different from GPGGA |