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

jbeale1 beale at bealecorner.com
Thu Jan 23 11:39:58 PST 2014

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 CORS
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

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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