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<a name="timing"></a>
<h2>PPS and GPSD:</h2>

<p>Many GPS receivers offer a 1PPS (one pulse per second) output that
  GPSD is capable of passing along to <code>ntpd</code> for use as an
  extremely accurate clock source.  The "Claimed Accuracy" are taken
  from manufacturers' data sheets, and have not been independently
  verified.</p>

  <p>Where specified, NTP time offsets have been measured by
  comparison with the NTP time service and reported by
  <code>gpsd</code>.</p>

  <p>Note that a direct RS-232 connection is required for optimal PPS
timing. Typical gpsd/PPS users report ntp clock stability on the order
of 1uS. GPS that use a RS-232 to USB converter that passes the PPS signal
are reported to be stable on the order of 1mS.GPS that are native USB are
not PPS capable but gpsd can still extract time information from the
serial data accurate to about 250mS.</p>

<div>&nbsp;</div>

<table border='1'>
<tr>
<th>Receiver</th>
<th>Claimed<br/>Accuracy</th>
<th>NTP time offset</th>
<th>Notes</th>
</tr>
<tr>
<td>SigNav TM3-01</td>
<td align="center">10ns</td>
<td align="center">-</td>
<td align="center">-</td>
</tr>
<tr>
<td>Trimble Thunderbolt E</td>
<td align="center">15ns</td>
<td align="center">-</td>
<td align="center">-</td>
</tr>
<tr>
<td>Trimble Resolution-T</td>
<td align="center">15ns</td>
<td align="center">-</td>
<td align="center">-</td>
</tr>
<tr>
<td>Motorola<br/>iLotus<br/>Synergy-GPS M12M</td>
<td align="center">20ns<br/>6ns corrected</td>
<td align="center">-</td>
<td align="center">-</td>
</tr>
<tr>
<td>NavSync CW25-TIM</td>
<td align="center">25ns</td>
<td align="center">-</td>
<td align="center">-</td>
</tr>
<tr>
<td>NavSync CW12-TIM</td>
<td align="center">30ns</td>
<td align="center">-</td>
<td align="center">-</td>
</tr>
<tr>
<td>Motorola OnCore UT+</td>
<td align="center">50ns</td>
<td align="center">-</td>
<td align="center">-</td>
</tr>
<tr>
<td>Trimble Lassen iQ</td>
<td align="center">50ns</td>
<td align="center">0.675sec</td>
<td align="center">-</td>
</tr>
<tr>
<td>Trimble Copernicus</td>
<td align="center">50ns</td>
<td align="center">-</td>
<td align="center">-</td>
</tr>
<tr>
<td>ublox Antaris</td>
<td align="center">50ns</td>
<td align="center">-</td>
<td align="center">-</td>
</tr>
<tr>
<td>ublox Antaris4</td>
<td align="center">50ns</td>
<td align="center">-</td>
<td align="center">-</td>
</tr>
<tr>
<td>ublox Antaris4T</td>
<td align="center">50ns<br/>15ns compensated</td>
<td align="center">-</td>
<td align="center">-</td>
</tr>
<tr>
<td>ublox Antaris 5</td>
<td align="center">50ns<br/>50ns</td>
<td align="center">-</td>
<td align="center">-</td>
</tr>
<tr>
<td>Novatel SuperStarII</td>
<td align="center">200ns</td>
<td align="center">-</td>
<td align="center">-</td>
</tr>
<tr>
<td>Thales AC12</td>
<td align="center">250ns</td>
<td align="center">-</td>
<td align="center">-</td>
</tr>
<tr>
<td>Garmin GPS18/LVC</td>
<td align="center">1usec</td>
<td align="center">0.125sec</td>
<td align="center">Must be outside with a clear sky view.<br>At 19200bps; drops to 0.525 at 4800bps</td>
</tr>
<tr>
<td>Rockwell Jupiter</td>
<td align="center">1usec</td>
<td align="center">-</td>
<td align="center">-</td>
</tr>
<tr>
<td>SiRFstar2</td>
<td align="center">1usec</td>
<td align="center">-</td>
<td align="center">-</td>
</tr>
<tr>
<td>SiRFstar3<br>(GlobalSat MR-350P)</td>
<td align="center">1usec</td>
<td align="center">-</td>
<td align="center">May work inside wood frame buildings.</td>
</tr>
<tr>
<td>Jackson Labs Firefly</td>
<td align="center">50ns</td>
<td align="center">-</td>
<td align="center">GPS-disciplined oscillator, so the 1PPS output stays accurate even if GPS receiption is lost.</td>
</tr>
</table>

<a name="raw"></a>
<h2>Raw Measurements and GPSD:</h2>

<p>All gpses require "raw" measurements internally to compute a navigation
  solution. The ability for users to postprocess these measurements is then
  a function of firmware and protocol support.</p>

<div>&nbsp;</div>

<table border='1'>
<tr>
<th>Receiver</th>
<th>Raw</th>
<th>Notes</th>
</tr>
<tr>
<td>NavSync</td>
<td align="center">No</td>
<td>I asked them about raw measurements and they told me that a custom firmware build ($$$!) would be required, and that I probably wasn't authorized to get that data.</td>
</tr>
<tr>
<td>SiRF</td>
<td align="center">Partial</td>
<td>sirfstar1 has raw data in message 5, sirfstar2 has raw data in message 28, sirfstar3 has some raw data in message 28 but carrier phase is not available. rumor has it that carrier phase is available as a premium feature in superstar3.</td>
</tr>
<tr>
<tr>
<td>ublox</td>
<td align="center">Partial</td>
<td>The RXM-RAW message contains raw data. This is implemented in all Antaris chips. This is only implemented in the timing versions of Antaris4. In ublox5 it is "only available with premium feature raw data".
</td>
</tr>
<tr>
<td>Novatel SuperStarII</td>
<td align="center">Partial</td>
<td>Message #23 contains raw measurements in carrier-phase-enabled firmwares.</td>
</tr>
<tr>
<td>Fastrax</td>
<td align="center">Yes</td>
<td>The "PSEUDO" message contains raw measurements</td>
</tr>
<tr>
<td>Trimble</td>
<td align="center">Yes</td>
<td>Packet 0x5a contains raw measurements</td>
</tr>
<tr>
<td>Thales AC12</td>
<td align="center">Yes</td>
<td>The PASHR,MCA message contains raw measurements.</td>
</tr>
</table>

</div>

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