There is an inherent DANGER in using ENC/vector charts.
You have to carefully note the 'magnification' of the original chart
and not exceed this limit as OVERMAGNIFICATION will result in some
pretty strange errors of 'resolution'.

One must remember that the 'basis' of many of the charts were leadline,
pelorous, etc. and to simply OVERMAGNIFY them can get you into serious
trouble real fast as the overmagnification is easy .... and very
foolish. Resolution errors are very easy to do on most of the NOAA
charts .... an example would be trying to read a 'yardstick' down to
0.001 inches. or reading a simple mercury theermometer to 0.01 degress.
You can do so with graphical magnification .... but the answer is
nearly ALWAYS wrong.



In article , Wayne.B
wrote:

On Thu, 14 Dec 2006 13:22:14 GMT, "Roger Long"
wrote:

The vector charts are also more difficult to
use, but that's a personal opinion. To me, vector charts just don't look
real; on my computer console a vector chart reminds me of a video game.

I agree with you on the appearance of vector charts but they have a
couple of advantages also that are not immediately obvious. For one,
they can be zoomed in or out to what ever degree of detail is
appropriate without becoming pixelated or having the type fonts
become too small. Another advantage is that they can be
electronically rotated and still have the fonts appear right side up.

Rich Hampel wrote:
... OVERMAGNIFICATION will result in some
pretty strange errors of 'resolution'.
....

I've not used the ENC charts but am very familiar with C-Map and
Transis vector charts. Over magnification with these systems produces
an image rendered with noticeable polygons. All of the chart rendering
programs I've used display warnings when over zoomed and some also
refuse to render over magnified charts. Anyway, I don't recall any
'strange errors of resolution.

One must remember that the 'basis' of many of the charts were leadline,
pelorous, etc. and to simply OVERMAGNIFY them can get you into serious
trouble real fast as the overmagnification is easy .... and very
foolish. ...

It would be nice if all the notes and diagrams that appear on paper
charts were always reproduced on the digital versions. If you are
looking at a chart that is based on a 19th century survey and has a
diagram of soundings that is mostly white then you are well advised to
keep a particularly good watch. I'm not sure that these kinds of
problems are more acute with digital media than with paper. However,
the digital chart error that I see getting most people into trouble is
using a non wgs correctable digital chart with a gps and has nothing to
do with magnification. Could you be more specific about the trouble
you have seen that has been caused by over magnification of vector
charts?

-- Tom.

On Thu, 14 Dec 2006 20:53:15 GMT, Rich Hampel
wrote:

ou can do so with graphical magnification .... but the answer is
nearly ALWAYS wrong.

Wrong is relative, and it depends on the chart. Most of my vector
charts for US waters with stable shorelines are accurate to within 50
or 60 feet. If you are 50 feet away from your charted position, is
that wrong? It depends. 99% of the time 50 feet is good enough to
bring you into line with a Mark I eyeball fix, and that's good enough
for me. For those areas with unstable inlets, shorelines and/or 1800s
survey data, the type of chart makes very little difference. They are
no better than a general guideline to get you started.

Here's what I think the OP is getting at:

http://home.maine.rr.com/rlma/Vector.jpg

CAD, which I also use a lot is vector based so lines are mathematically
thin. They don't get thicker as you zoom in. The view on the left, drawn
with CAD, is true scale so the boat is a comfortable distance from the
sounding line.

In the view on the right, the line is zoomed 1000 times. If the system
generated icon showing your boat doesn't scale at the same time as the view,
you get an image which makes it look like you are still a comfortable
distance off. But, it this view, the distance to the sounding line is only
a few inches. Throw in normal chart inaccuracy and, THUNK!

--
Roger Long

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.

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

Comments to several msg's in this thread without attribution:
1. The greatest advantage to paper charts over either vector or raster is
the zoom & pan speed.
2. Not disputing the definition of a vector, which indeed has no thickness.
But, every cad system that I've used, and there are quite a few, are capable
of drawing lines with thickness and the thickness does scale.
3. The NOAA ENC charts do seem to have thickness for their lines.
4. Fugawi limits the zoom scale on vector charts to 1000, whatever that
number means with respect to vectors. So, I can't fully test my line
thickness hypotheses.
5. Not 100% sure, more like 10%, but I'm of the impression that NOAA is
creating / recreating / updating the ENC charts from satellite surveys.
BF

"Roger Long" wrote in message
...
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

BF wrote:

2. Not disputing the definition of a vector, which indeed has no
thickness. But, every cad system that I've used, and there are quite
a few, are capable of drawing lines with thickness and the thickness
does scale.

Certainly, you can always draw or convert to a polyline and assign thickness
but this wasn't meant to be a discussion about CAD.
If vector chart systems use something similar, which would increase the data
storage file sizes significantly, then the OP must be talking about
something different than what I demonstrated.

--
Roger Long

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.

Thats precisely the argument.
If your chart is accurate to only 60 ft., if you apply a magnification
of 10X, the accuracy is STILL 60 ft. and not the (apparent) visual 6ft.
that would be the 'new resolution' at an increase of magnification @
10X.


In article , Wayne.B
wrote:

On Thu, 14 Dec 2006 20:53:15 GMT, Rich Hampel
wrote:

ou can do so with graphical magnification .... but the answer is
nearly ALWAYS wrong.

Wrong is relative, and it depends on the chart. Most of my vector
charts for US waters with stable shorelines are accurate to within 50
or 60 feet. If you are 50 feet away from your charted position, is
that wrong? It depends. 99% of the time 50 feet is good enough to
bring you into line with a Mark I eyeball fix, and that's good enough
for me. For those areas with unstable inlets, shorelines and/or 1800s
survey data, the type of chart makes very little difference. They are
no better than a general guideline to get you started.