DPRG mailing list archives: [DPRG] Re: WAAS success on GPS...

Thu May 22 22:06:26 CDT 2008

Jeff & DPRG,

I have some raw data to share with you related to the recent restart into
the robotics hobby and the work on GPS that Jeff got me restarted in...

The first two data sets come from this past fall/early winter before I had
differential GPS working.  The really interesting part is to compare group 3
and group 4.

Module: 32-Channel Etek GPS (from Spark Fun)  The OEM module used in this
product is the EB85 radio module with integral SiRF III chipset.

Group 1
Legacy Data: Data collected without Differential GPS, without ground plane.
Data sets collected for 24 continuous hours (all roughly consistent
weather), data sets collected (7), Unit stationary, indoors downstairs,
minimum satellites in calculation (7), minimum number of satellites in view
(10), Worst Error 288ft*, average error 60ft-SSE.
*Error cloud not symmetrical, Each of the 7 runs had a significantly
different centeroid, so the average error here is not really telling.

Group 2
Legacy Data collected without differential GPS, this time a ground plane
~6in square is added.
Data sets collected for 24 continuous hours drastic weather conditions, data
sets collected (4), Unit stationary, indoors, downstairs, minimum satellites
in calculation (7), minimum number of satellites in view (9), worst Error
58ft, average error 10ft-SSE.
*Error cloud not symmetrical, Each of the 4 runs had a different centeroid,
two of them were only different by ~4ft, the other two were further out..

Group 3
Data collected with differential GPS and ground plane ~6in square.
Data Sets collected for 24 continuous hours, extreme weather conditions
(lightning storms (2x), Hail, etc), data sets collected (6) Unit stationary,
indoors, downstairs, minimum satellites in calculation (6), minimum number
of satellites in view (8), worst error 26ft*, average error 2ft.
*Error cloud almost symmetrical forming an roughly even ellipse around the
actual position,  The error centeroid between each of the 6 data sets only
deviated by ~5 feet.

Group 4
Data collected with differential GPS and the ground plane removed
Data sets collected for 24 continuous hours, extreme weather conditions,
lightening storms (1x), torrential rain & interspersed sunshine, data sets
collected (7) Unit stationary, indoors, downstairs, minimum satellites in
calculation (6), minimum number of satellites in view (7), worst error
24ft*, average error 0ft.
*Error cloud symmetrical forming an ellipse around the actual position.  The
error centeroid between each of the 7 runs deviated by only ~2 ft.

Next steps:  Add variables to track largest rate of change, largest single
change between data points, largest change over 5min, 10min and 1hr rolling
windows.  I still haven't finished off the code to dump the raw data back to
the PC yet either for analysis with Excel or other for more in-depth
analysis.

The observations that Jeff and the group may be interested in are the very
similar results for this particular module once in DGPS mode with and
without ground plane.  Where might this kind of data accuracy be applicable?
Driving around the block (my block) which is 3/4mile in circumference, or in
DPA's challenge #5.  He may not know it yet but that one is on the scale of
miles not hundreds of feet where the error of 6ft / 1000ft may come into
play.   Am I truly suggesting such a competition, no not really, just making
an observation on the scale of the error.

-Kenneth

-----Original Message-----
From: dprglist-bounces at dprg.org [mailto:dprglist-bounces at dprg.org]On
Behalf Of Jeff Sampson
Sent: Sunday, May 04, 2008 3:35 PM
To: Kenneth Maxon
Cc: dprglist at dprg.org
Subject: [DPRG] Re: WAAS success on GPS...

Kenneth Maxon wrote:
> Jeff,
>

> I'd like to report Success in (after all this time) getting WAAS signaling
> back from the SMIRF(III) chipset.

Great! It will be interesting to see how much improvement you will get
with the WAAS turned on.

--
Jeff Sampson
http://tcrobots.org/members/jsamp.htm
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