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Old 30-03-2019, 14:02   #1
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Raster or Vector charts or BOTH?

In another thread (http://www.cruisersforum.com/forums/...ts-215681.html), there were comments from some folks about how they prefer raster charts, compared to vector.

In this article "How to use vector charts safely https://www.yachtingmonthly.com/sail...s-safely-33747" from a few years ago, Tom Cunliffe makes a good case why relying on vector charts alone can lead to unhappy endings.

As well as all the other data sources required for safe navigation, I'm now persuaded that vector charts should be supplemented by raster charts for any of the areas I currently or intend to sail. Using OpenCPN, it is simple to have both ENC and RNC installed and flip back and forth as required.

Lots of good, solid common sense in that article. Interested in your thoughts...
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Old 30-03-2019, 14:19   #2
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Re: Raster or Vector charts or BOTH?

Horses for courses.


Vector for your chart plotter -- for pilotage, not navigation. You can zoom smoothly; the picture is more appropriate on a small screen. I have one raster chart set for my nav system -- it is definitely more awkward and much less satisfactory than the Navionics vector ones.


Raster for navigation and passage planning, on a big screen. Vector is not good for this. If you look in the archives, you will find striking screenshots showing the remarkable difference in the level of detail possible in a zoomed out view, something you need for passage planning. Using a raster chart on a large screen is similar to using a paper chart.


For UK and European Atlantic coasts, the brilliant VisitMyHarbour sets of raster charts, officially "for navigation", and hundreds of up to date charts for what you would pay for 3 or 4 paper charts. I wish they published them for other areas.



For US waters, I guess you can get them free from NOAA.
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Old 31-03-2019, 04:10   #3
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Re: Raster or Vector charts or BOTH?

We use both raster and vector, one each on the plotter and at least one handheld back-up device, and even sometimes simultaneously on the plotter too. Instant zoom on both.

-Chris
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Old 31-03-2019, 09:38   #4
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Re: Raster or Vector charts or BOTH?

Note this article...

https://www.workboat.com/news/coasta...utical-charts/

Says a couple interesting things. One is that vector charts are updated before raster charts. (Didn't know that; in fact, though it was the other way round.)

The other is that vector charts will show continue to show controlling (observed) depths, while raster charts will gradually be changed to show project depths.

I interpret that to mean depths on raster and vector charts won't always agree.

-Chris
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Old 31-03-2019, 11:09   #5
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Re: Raster or Vector charts or BOTH?

Quote:
Originally Posted by ranger42c View Post
Note this article...

https://www.workboat.com/news/coasta...utical-charts/

Says a couple interesting things. One is that vector charts are updated before raster charts. (Didn't know that; in fact, though it was the other way round.)

The other is that vector charts will show continue to show controlling (observed) depths, while raster charts will gradually be changed to show project depths.

I interpret that to mean depths on raster and vector charts won't always agree.

-Chris

The link in that article to the official NOAA announcement has even more details https://www.nauticalcharts.noaa.gov/updates/?p=171708.

Quote:
Over the next few years, mariners will see continued improvement in the extent and detail of ENC coverage, while there will be a reduction in RNC and paper chart coverage and service.
Looks like the writing is on the wall for RNCs and paper. Seems unfortunate, since RNCs provide a different view and even additional information not present in ENCs.
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Old 31-03-2019, 13:22   #6
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Re: Raster or Vector charts or BOTH?

Quote:
Originally Posted by Shawanaga View Post
Looks like the writing is on the wall for RNCs and paper. Seems unfortunate, since RNCs provide a different view and even additional information not present in ENCs.
I think you're right. I don't know why the maritime community doesn't demand that all the data from the raster charts be digitized, and correctly, before phasing them out.

I get why agencies would want to go with only one format, but I find it unfathomable that they would leave so much data behind in the old format, and leave so many errors from the digitizing process in the new format.
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Old 31-03-2019, 15:54   #7
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Re: Raster or Vector charts or BOTH?

Quote:
Originally Posted by ranger42c View Post
Note this article...

https://www.workboat.com/news/coasta...utical-charts/

Says a couple interesting things. One is that vector charts are updated before raster charts. (Didn't know that; in fact, though it was the other way round.)

The other is that vector charts will show continue to show controlling (observed) depths, while raster charts will gradually be changed to show project depths.

I interpret that to mean depths on raster and vector charts won't always agree.

-Chris

It's logical, if you think about it. Raster charts are digitized charts made by human cartographers. Naturally they are updated more slowly, because the new information goes through human hands. That is at the same time the weakness and the great strength of raster charts -- they are real charts, showing data interpreted by real cartographers applying actual judgement.


Vector charts, on the other hand, are a computer-generated picture (generated right by your own chart plotter) made out of a bunch of data. It's easy to update because you just dump the data in -- no need for any interpretation.


It will be a great shame if raster charts are discontinued by NOAA. Vector charts are not a substitute. I hope that this will not happen anytime soon in Europe. The British Admiralty charts are works of art, and a great pleasure to use, even in electronic form (which preserves all the detail, even the notes).
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We must have a turn together . . . . I undress . . . . hurry me out of sight of the land,
Cushion me soft . . . . rock me in billowy drowse,
Dash me with amorous wet . . . . I can repay you."
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Old 31-03-2019, 16:05   #8
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Re: Raster or Vector charts or BOTH?

Each seems to serve a different need, we have both.
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Old 31-03-2019, 16:06   #9
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Re: Raster or Vector charts or BOTH?

I’m used to Admiralty charts, but we are fortunate here in NZ that the hydrographic office have elected to provide all the raster charts for country free online, regularly updated with a monthly download pack. Using SeaIQ on an iPad these are fabulously smooth and quick to zoom to any level. My fourth-emergency-chart-plotter uses Navionics vector charts, which are laughably bad by comparison.

One of my main concerns preparing for a trip around the South Pacific is what to do about good up to date electronic charts. I’m not even sure whether good electronic raster charts are easily available. Can someone tell me where the best source of these is?
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Old 31-03-2019, 16:28   #10
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Re: Raster or Vector charts or BOTH?

Quote:
Originally Posted by Dockhead View Post
It's logical, if you think about it. Raster charts are digitized charts made by human cartographers. Naturally they are updated more slowly, because the new information goes through human hands. That is at the same time the weakness and the great strength of raster charts -- they are real charts, showing data interpreted by real cartographers applying actual judgement.
Are they? Seems like you would expect but a quick google...

What is the difference between a raster chart and a vector chart
Hints that it's the same data >
Quote:
ENCs are vector charts or "smart charts" and are coded with additional information not available in paper or raster charts.
https://catalog.data.gov/dataset/noa...harts-rnc7af22
And again >
Quote:
The charts are currently available as Lithographically printed paper charts, Electronic Raster Nautical Charts (RNCs), up-to-date paper charts (printed with print on demand technology), and are now offered as Digital Vector Electronic Nautical Charts (ENC).
No mention of extra care taken for raster charts.

Anyone know of any examples of data being "more correct" on a raster chart than the equivalent vector chart. Istr reading that raster charts are created from the exact same vector chart data tweaked to make it look nice. But could be wrong..
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Old 31-03-2019, 16:32   #11
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Re: Raster or Vector charts or BOTH?

Quote:
Originally Posted by Tillsbury View Post
One of my main concerns preparing for a trip around the South Pacific is what to do about good up to date electronic charts. I’m not even sure whether good electronic raster charts are easily available. Can someone tell me where the best source of these is?
Are there any up to date charts for many areas like that? Google satellite images can be gold dust for a lot of places. And marinetraffic density overlay well worth checking as well.

As for either/or..... YES!!!. Anything and everything available! So much simpler these days with opencpn and mbtiles.
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Old 31-03-2019, 17:13   #12
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Re: Raster or Vector charts or BOTH?

I’m thinking that google earth may well be a primary source. Has anyone collated good sets of kap or similar files for some areas, or do we just get on with it ourselves?
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Old 31-03-2019, 17:38   #13
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Re: Raster or Vector charts or BOTH?

Quote:
Originally Posted by conachair View Post
Are they? Seems like you would expect but a quick google...

What is the difference between a raster chart and a vector chart
Hints that it's the same data >


https://catalog.data.gov/dataset/noa...harts-rnc7af22
And again >


No mention of extra care taken for raster charts.

Anyone know of any examples of data being "more correct" on a raster chart than the equivalent vector chart. Istr reading that raster charts are created from the exact same vector chart data tweaked to make it look nice. But could be wrong..

More than you ever wanted to know about it explained here:


https://chersoft.com/Resources/CherS...sterVector.pdf


"The key difference between raster and vector charts is in the way in which they are rendered, where rendering is process of translating the chart data into an image which can then be displayed on the screen. The screen is always raster display, that is, it is made up of dots. So:


"A raster chart is early rendered. The source data is analysed by a hydrographic office and the chart is drawn by a cartographer. The final image is decided by a cartographer and this image is captured for display on a computer screen.


"A vector chart by contrast is late rendered. In this case the hydrographic office collates a set of (vector) data which can be used to generate a chart image. However, the image is drawn by the computer and this is not actually done until just before it is displayed on the screen.

. . . .



"Early rendering means basically letting the cartographer do his job. This work is not only highly skilled but also time consuming. It is not unknown for a cartographer to literally spend all day looking at a new edition of a chart just to make sure that the layout and labelling and detail and myriad other factors are all just so; just right to make the chart clear, concise, uncluttered and useful for the navigator."



So, as I said, raster charts are images of human-drawn charts, whereas vector charts are computer-drawn charts based on databases of data pulled out of raster charts.



The human-drawn charts represented in paper or raster charts are discrete views interpreted by real cartographers -- these views are absolutely invaluable for passage planning -- there is a lot of advice and discretion embodied in them -- the cartographer is showing what his professional knowledge tells him you need to know -- he's talking to you. Each view (which corresponds to a separate paper chart) has the right amount of detail for that view; you don't have the "zoom problem" of vector charts and you generally have far too much information to display useably on a small screen but just the right amount of information to visualize a whole passage and different significant parts of it.


Vector charts are created on the fly by a computer, and according to the exact zoom level you need, so are not limited to a limited set of views as are raster charts, but the views are mechanistically created and always lack important detail when zoomed out. This makes them better for pilotage and for use in chart plotters. But they are dreadful for passage planning, with regularly fatal results, which is why on my boat there is always a vector chart in the plotter at the helm and boat nav system, and a raster chart on a large 4k monitor at the nav table, rendered by OpenCPN, or else a paper chart.


Except in Danish waters, where I don't have any vector charts other than CM93, so I use an NV Charts raster chart chip, which doesn't work very well in the B&G Zeus nav system.



Read the linked white paper for more information.
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"You sea! I resign myself to you also . . . . I guess what you mean,
I behold from the beach your crooked inviting fingers,
I believe you refuse to go back without feeling of me;
We must have a turn together . . . . I undress . . . . hurry me out of sight of the land,
Cushion me soft . . . . rock me in billowy drowse,
Dash me with amorous wet . . . . I can repay you."
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Old 31-03-2019, 17:40   #14
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Re: Raster or Vector charts or BOTH?

This is also an excellent resource:


Marine Chartplotters... Raster vs Vector explained : by VisitMyHarbour [Overview-VMH products and downloads] - VisitMyHarbour articles
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I behold from the beach your crooked inviting fingers,
I believe you refuse to go back without feeling of me;
We must have a turn together . . . . I undress . . . . hurry me out of sight of the land,
Cushion me soft . . . . rock me in billowy drowse,
Dash me with amorous wet . . . . I can repay you."
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Old 31-03-2019, 17:45   #15
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Re: Raster or Vector charts or BOTH?

Another good explanation:
https://mytimezero.com/raster-vs-vector
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