On 26 June, 14:29, IanM wrote:
alt.sailing.asa xpost dropped in the hope of having a reasoned technical
discussion :-)



John Navas wrote:
On Fri, 25 Jun 2010 08:38:28 -0400, in
s.com, "Wilbur
Hubbard" wrote:

"Tim Thornton" wrote in message
....

TeamSurvis a project to help create better charts of coastal waters,
by getting sailors to log GPS and depth data - seewww.teamsurv.eufor
more information. For example, in Britain the UKHO states that only
50% of Britain's coastal waters are adequately surveyed, and they
concentrate on areas used by commercial shipping. JoinTeamSurvand
help update the charts and fill in the gaps.
...
What an IGNORANT idea. What you're trying to do is make a Wikipedia Charts
system. In other words, something any inept fool can contribute to and make
the entire effort something that can't be relied upon.

Bad idea - an example of stupid liberal thinking. Sailing by a committee of
amateurs and wannabes!

AMEN!

Done well, this could be very good. *Done poorly, it would be no worse
than the quality of 'local knowlage' to be gained in the bar from the
club bore or wannabe.

Lets assumeTeamSurvhave done their homework:

1. Prefer vessels based in locked marinas. * Reason: passing over the
lock sill allows the data sequence to be checked for incorrect GPS datum
and the depthsounder offset to be calibrated.

2. Discard sequences where the track/depth data cannot be reconciled
with recently surveyed features. * Reason: Depth sounder calibration and
anti-tamper precautions

3. Encrypt the data sequences and store ALL available NMEA data + logger
local time. *Reason: Anti-tamper precaution - Anyone reasonably
competent can fake a NMEA position sentence + bogus depth data, but to
successfully tamper with the whole dataset for a voyage would be much
harder.

4. Compare the data sets from multiple voyages and vessels to 'rate'
each data set and even each vessel for accuracy.

At the very least this could be used to highlight areas that urgently
need re-surveying *and I can think of half a dozen shoals or bars that
tend to move in winter storms in my *usual sailing area that I would be
glad to have even one recent track with depths over.

Its a high tech version of following the yacht in front of you, but at
least you know its not a *Southerly with the keel cranked up!

--
Ian Malcolm. * London, ENGLAND. *(NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk
[at]=@, [dash]=- & [dot]=. *Warning* HTML & 32K emails -- NUL:

Ian,
We work along much of what you say.
For point 1, we require each boat that joins to go through a
calibration porocedure before we process their data
We don't do 2 explicitly, but as part of the QA we compare results
against bathymetric survey data where possible or, failing that,
against chart data
3 - we do record all NMEA data, both for security and also it gives us
better accuracy, e.g. temperature helps feed in to speed of sound
corrections, and heading is better than COG to correct for the
displacement between GPS antenna and depth transducer.
4 - we will do this as we get a high enough density of data in areas.
Tim