[FOSS-GPS] RTKLIB, uBlox LEA-6T. PPP-Static to 10 cm. Is it real?

Josh Leighton leighton.josh at gmail.com
Thu Jan 23 12:03:30 PST 2014

While I haven't used RTKLIB's PPP mode much, I have played around with some
ublox NEO-6P modules and their built in PPP.  We observed stationary
precision on the order of ~30cm in a fairly noisy environment with less
than ideal sky visibility, and also using an inexpensive puck antenna.
 Based on this, your results don't seem unreasonable.

Of course that's only when stationary.  Once we started moving the
receivers the PPP-enabled transmitter performed worse than the two other
ublox units without it.

On Thu, Jan 23, 2014 at 2:39 PM, jbeale1 <beale at bealecorner.com> wrote:

> After taking advantage of the $35 deal on the SSR-6Tr board from Synergy
> Systems, I have my u-blox LEA-6T-0 logging RXM-SFRB, and at 5-second
> intervals RXM-RAW messages. Antenna is a $6 puck from Ebay sitting flat on
> the peak of a metal tile roof, with a clear sky view in nearly all aziumuth
> directions down to 10 degrees elevation, and signal going through about 130
> feet of RG-6/U coax into a 3-way 2GHz CATV splitter (for possible
> comparison
> with other units, although I'm not doing that now).
> I am using RTKCONV & RTKPOST version 2.4.2 in "PPP Static" mode with
> "Combined" fwd/back filter, 35 dB/Hz cutoff on all elevations and GPS+SBAS.
> Ignoring a few obvious single-point outliers (phase slips?) over a 24 hour
> time period, the solution ground track fits into a box 10 cm (E/W) x 6 cm
> (N/S). STD=E: 0.0295m N: 0.0205m U: 0.0900m
> The following day, a second 24 hour data set gives me a track 15 cm x 5 cm
> and STD=E: 0.0526m N: 0.0131m U: 0.0303m and the two days' results differ
> overall by about 6 cm.  I played with doing 0, 5, 10 and 15 degree cutoffs,
> but found I got the best (lowest deviation) results using the whole sky.
> So this gives the appearance of a consistent solution at the 10 cm level.
> This seems almost too good to believe. Note I am not using any external
> data, just what is broadcast and logged directly by a single LEA-6T
> receiver. Is this performance expected of PPP mode from a cheap L1-only
> system?
> I haven't tried observing at a known geodetic reference point so I can only
> speak to apparent precision, not absolute accuracy. If my solution is good,
> the google maps satellite image appears to be about 50 cm off at my
> location
> in San Jose, CA.
> I also tried a Static solution pairing with CORS base station but the
> closest one is about 25km away and the result was a very scattered cloud of
> points about 5 m in diameter, so probably I am doing something wrong.
> --
> View this message in context:
> http://open-source-gps-related-discussion-and-support.1099874.n2.nabble.com/RTKLIB-uBlox-LEA-6T-PPP-Static-to-10-cm-Is-it-real-tp7572802.html
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