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- <!-- Changed by: Harlan &, 31-Mar-2014 -->
+ <!-- Changed by: Pearly &, 04-Feb-2019 -->
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<h3>Generic NMEA GPS Receiver</h3>
<p>Last update:
- <!-- #BeginDate format:En2m -->31-Mar-2014 03:55<!-- #EndDate -->
+ <!-- #BeginDate format:En2m -->04-Feb-2019 07:30<!-- #EndDate -->
UTC</p>
<hr>
<h4>Synopsis</h4>
second insertion in UTC. To avoid problems mixing UTC and GPS
timescales, the driver disables processing of UTC sentences
once <tt>$GPZDG</tt> is received.
+ <br>
+ <strong>Caveat:</strong> Please see <a href="#talkerids">Talker
+ IDs</a> when using non-GPS or multi-system receivers.
</p>
<p>
The driver expects the receiver to be set up to transmit at least one
</tr><tr>
<td class="ttf">$GPZDG,GPSTIME,DD,MM,YYYY,AA.BB,V*CS<cr><lf></td>
<td>Accord</td>
- </tr>
+ </tr><tr>
+ </tr><tr>
+ <td class="ttf">$PGRMF,GWEEK,WTIME,DATE,UTC,LEAPS,LAT,LAT_REF,LON,LON_REF,TYPE,MODE,SPD,HDOP,TDOP*CS<cr><lf></td>
+ <td>Garmin</td>
+ </tr>
</tbody></table></p>
<p><table class="dlstable" border="1">
</tr>
<tr>
- <td class="ttf">UTC</td>
- <td>Time of day on UTC timescale. Hours, minutes and seconds [fraction (opt.)]. (hhmmss[.fff])</td>
- </tr><tr>
- <td class="ttf">POS_STAT</td>
- <td>Position status. (A = Data valid, V = Data invalid)</td>
+ <td class="ttf">ALT</td>
+ <td>Antenna Altitude</td>
</tr><tr>
- <td class="ttf">LAT</td>
- <td>Latitude (llll.ll)</td>
+ <td class="ttf">ALT_UNIT</td>
+ <td>Altitude Units (Metres/Feet)</td>
</tr><tr>
- <td class="ttf">LAT_REF</td>
- <td>Latitude direction. (N = North, S = South)</td>
+ <td class="ttf">DATE</td>
+ <td>Date (ddmmyy)</td>
</tr><tr>
- <td class="ttf">LON</td>
- <td>Longitude (yyyyy.yy)</td>
+ <td class="ttf">DD</td>
+ <td>Day of the month (1-31)</td>
</tr><tr>
- <td class="ttf">LON_REF</td>
- <td>Longitude direction (E = East, W = West)</td>
+ <td class="ttf">D_AGE</td>
+ <td>Age of last DGPS Fix</td>
</tr><tr>
- <td class="ttf">SPD</td>
- <td>Speed over ground. (knots) (x.x)</td>
+ <td class="ttf">D_REF</td>
+ <td>Reference ID of DGPS station</td>
</tr><tr>
- <td class="ttf">HDG</td>
- <td>Heading/track made good (degrees True) (x.x)</td>
+ <td class="ttf">FIX_MODE</td>
+ <td>Position Fix Mode (0 = Invalid, >0 = Valid)</td>
</tr><tr>
- <td class="ttf">DATE</td>
- <td>Date (ddmmyy)</td>
+ <td class="ttf">GEO</td>
+ <td>Geoid/Elipsoid separation</td>
</tr><tr>
- <td class="ttf">MAG_VAR</td>
- <td>Magnetic variation (degrees) (x.x)</td>
+ <td class="ttf">GPSTIME</td>
+ <td>Time of day on GPS timescale. Hours, minutes and seconds [fraction (opt.)] (hhmmss[.f])</td>
</tr><tr>
- <td class="ttf">MAG_REF</td>
- <td>Magnetic variation (E = East, W = West)</td>
+ <td class="ttf">GWEEK</td>
+ <td>Week number in the GPS time scale, modulo 1024 (0..1023)</td>
</tr><tr>
- <td class="ttf">FIX_MODE</td>
- <td>Position Fix Mode (0 = Invalid, >0 = Valid)</td>
+ <td class="ttf">G_UNIT</td>
+ <td>Geoid units (M/F)</td>
</tr><tr>
- <td class="ttf">SAT_USED</td>
- <td>Number of Satellites used in solution</td>
+ <td class="ttf">HDG</td>
+ <td>Heading/track made good (degrees True) (x.x)</td>
</tr><tr>
<td class="ttf">HDOP</td>
<td>Horizontal Dilution of Precision</td>
</tr><tr>
- <td class="ttf">ALT</td>
- <td>Antenna Altitude</td>
+ <td class="ttf">LAT</td>
+ <td>Latitude (llll.ll)</td>
</tr><tr>
- <td class="ttf">ALT_UNIT</td>
- <td>Altitude Units (Metres/Feet)</td>
+ <td class="ttf">LAT_REF</td>
+ <td>Latitude direction (N = North, S = South)</td>
</tr><tr>
- <td class="ttf">GEO</td>
- <td>Geoid/Elipsoid separation</td>
+ <td class="ttf">LEAPS</td>
+ <td>Leap seconds or difference between GPS time scale and UTC</td>
</tr><tr>
- <td class="ttf">G_UNIT</td>
- <td>Geoid units (M/F)</td>
- </tr><tr>
- <td class="ttf">D_AGE</td>
- <td>Age of last DGPS Fix</td>
+ <td class="ttf">LON</td>
+ <td>Longitude (yyyyy.yy)</td>
</tr><tr>
- <td class="ttf">D_REF</td>
- <td>Reference ID of DGPS station</td>
+ <td class="ttf">LON_REF</td>
+ <td>Longitude direction (E = East, W = West)</td>
</tr><tr>
- <td class="ttf">GPSTIME</td>
- <td>Time of day on GPS timescale. Hours, minutes and seconds [fraction (opt.)]. (hhmmss[.f])</td>
+ <td class="ttf">MAG_REF</td>
+ <td>Magnetic variation (E = East, W = West)</td>
</tr><tr>
- <td class="ttf">DD</td>
- <td>Day of the month (1-31)</td>
+ <td class="ttf">MAG_VAR</td>
+ <td>Magnetic variation (degrees) (x.x)</td>
</tr><tr>
<td class="ttf">MM</td>
<td>Month of the year (1-12)</td>
+ </tr><tr>
+ <td class="ttf">POS_STAT</td>
+ <td>Position status. (A = Data valid, V = Data invalid)</td>
+ </tr><tr>
+ <td class="ttf">SAT_USED</td>
+ <td>Number of Satellites used in solution</td>
+ </tr><tr>
+ <td class="ttf">SPD</td>
+ <td>Speed over ground. (knots) (x.x)</td>
+ </tr><tr>
+ <td class="ttf">UTC</td>
+ <td>Time of day on UTC timescale. Hours, minutes and seconds [fraction (opt.)] (hhmmss[.fff])</td>
+ </tr><tr>
+ <td class="ttf">WTIME</td>
+ <td>GPS week time, seconds since start of GPS week (0..604799)</td>
</tr><tr>
<td class="ttf">YYYY</td>
<td>Year</td>
</tbody></table></p>
+ <h4><a name="talkerids"/>NMEA Talker IDs</h4>
+
+ <p>
+ GNSS receivers use a distinct talker ID for the GNSS they
+ process. Recivers capable of tracking different systems at the same time
+ can emit <tt>$GPRMC</tt> (GPS), <tt>$GLRMC</tt> (GLONASS),
+ <tt>$GARMC</tt> (Galileo), <tt>$GNRMC</tt> (generic/combined) and others
+ all in one data stream.
+ </p><p>
+ The driver supports this to a certain degree by ignoring the
+ talker ID on the standard sentences RMC, GLL, GGA, ZDA and ZDG. (It
+ possibly should not do that on the latter, but for now, that's the way
+ it is.) So whenever <tt>$GPRMC</tt> is mentioned in this document,
+ substitute any possible talker ID your receiver might emit -- it will
+ still match.
+ </p><p>
+ This approach has a drawback. It is easy to use for single-system
+ receivers, but it cannot separate the data streams for multi-system
+ receiver modules. It is therefore undefined which GNSS actually
+ provides the data, and this can lead to strange behavior. This is
+ especially true if the different GNSS provide very different signal
+ quality to the receiver; the driver is not able to cherry-pick the best
+ source and might actually end up in using the worst available. It is
+ therefore recommended to set up such a receiver to either use just a
+ single GNSS (which would defeat its purpose) or to emit only the
+ combined data, which usually has the <tt>GN</tt> talker ID defined by
+ the NMEA standard.
+ <p>
+
+
<h4>The 'mode' byte</h4>
<p>
<td align="center">0</td>
<td align="center">1</td>
<td align="center">1</td>
- <td>process <tt>$GPMRC</tt></td>
+ <td>process <tt>$GPRMC</tt></td>
</tr><tr>
<td align="center">1</td>
<td align="center">2</td>
projects / thirdparty / ntp.git / commitdiff
