On Fri, 15 Dec 2006 14:57:34 +0000, Roger Long wrote:

Being in the business of drawing stuff, it makes sense to me.

Raster charts are machine images of the "gold standard" the NOAA paper
charts. Conversion to vector is a massive process that requires tracing
every feature. It's too large a job for incorporating human judgement on
every detail but requires too much human judgement and pattern recognition
for a machine to be entrusted with the whole task. The result is an
overwhelming number of places for errors to creep in.

I've tried several methods of converting raster scans of my old hand drawn
plans into vector CAD. It takes almost as long to clean them up as to have
just traced them from scratch. Until NOAA starts drawing the charts in
vector form from the get go, I don't see any way that vector charts are
going to be as reliable in any probable economic scenario.

I don't know if they've started yet, but the new "gold standard" will
be the raw database of soundings, GPS points, etc., from which the new
vector charts will be drawn. The beauty of this is that charts can more
readily be updated by simply updating the database, or just parts of it
(for the stuff that actually changes). Also, more layers of information
can be included, and displayed (or not) as desired. Finally, if you want
a raster chart or a paper copy, it's easy enough to print one from the
master vector format, though not the other way around (as you've
discovered.)

There was a pretty good basic article about all this in Sail magazine a
couple of years ago, but unfortunately, the marine "press" has not kept up
with the reporting. Government websites are always byzantine and running
way behind too. The information may be there, but unless you know about
it ahead of time and know where to look, you'll never find it. The
government is not very good with information about their information, so
to speak.

Matt O.