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.


Jeff wrote:
Submitted for your approval:

Here are two pics taken from Coastal Explorer using raster and vector
charts of Vineyard Haven. The photo is superimposed, merged in about
50%.

http://www.sv-loki.com/VHVectorPhoto.jpg
http://www.sv-loki.com/VHRasterPhoto.jpg

Note that in the Vector version, many of the features are mis-aligned.
In particular, the breakwater falls short about 100 feet, which
could cause an embarrassing situation in the fog.

These charts were what "came" with the system, there was no special
effort to setup certain charts - I simply zoomed on on one of my
favorite spots and selected vector and then raster charts only.

The raster chart is 1:10,000 "HARBOR" type, 4/1/06
The vector chart is also listed as "HARBOR" but is only 1:40,000.
If you click on the correct info panel, it shows the following in red:

"WARNING! The data in this area is incomplete. Dangers to
navigation exist in this area and are not included. The mariner
is advised to use the corresponding largest scale raster or paper
chart to navigate in this area."

So I looked around for another chart of the area and found one that
was also 1:40,000 but included more detail:

http://www.sv-loki.com/VHVector2Photo.jpg

This did not have the same "short breakwater" problem but its hard to
say it was more accurate.

As much as I like reviewing vector charts in the comfort of my home,
or down below, I still happy to use paper as my primary reference in
the cockpit.

--
Roger Long