Re: [gpsd-users] New FAQ question

[Eric S. Raymond]

John W. Nicholson <address@hidden>:
> Q: How to determent if WAAS is working and active while gpsd is running? If 
> WAAS is not working, how to make it work?

<h1 id='waas'>How can I tell if WAAS/EGNOS is working?</h1>

<p>In your skyview, look for GPS sats with numbers 120 and above;
those are the WAAS/EGNOS birds. For U.S. users 138 is the most likely
PRN to show up. If your GPS receiver can see them at all, it can
probably use them for correction when you're within range of a
WAAS/EGNOS ground station. But you can't be sure of this unless
they're marked as part of the satellite set for a fix. On the other
hand, some receivers may use them <em>without</em> marking the WAAS/EGNOS
satellites as part of the fix set. Vendor documentation in this area
tends to be murky or nonexistent.</p>

<p>If your receiver emits the NMEA GGA sentence, look at field 6 right
after the E or W qualifier for the latitude.  This is the GPS fix
quality indicator field. 2 indicates that the receiver is getting and
using differential-GPS corrections.  On a consumer-grade GPS this
usually means WAAS/EGNOS is in use.</p>

<p>Note that for WAAS to work, you need to be within 500 miles of a
WAAS ground station.  At present (2013) coverage is only available
in the U.S., Europe, and the near ocean waters of these regions.</p>

<p>Unfortunately, the mere presence of "WAAS" in your receiver's
feature list is not a guarantee that WAAS is actually supported.  This
feature causes significant additional power usage, and OEMs sometimes
condition it out of their firmware builds without documenting that
fact.</p>

<p>It has been found that while SiRF-II chips generally had WAAS
working, SiRF-III support varies by firmware level.</p>

> Q: How to have 4 GPS units working at the same time on one computer? 

Just plug them all into USB ports. GPSD should find and report fixes
from them all.  It won't do averaging or smoothing, though. You'll
have to customize your application to do that.
-- 
                <a href="http://www.catb.org/~esr/";>Eric S. Raymond</a>