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Old 29-06-2011, 14:37   #1
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Chart Images NOAA 25609 BVI

Hi,

I was recently able to snag images of the NOAA British Virgin Islands chart #25609 "from various sources to 1986". It takes hours for me to stitch these together from publicly available images. It's not new, but it's a real high resolution chart image begging to be converted into RNC format through various wizardry. I wanted to get this out there in the hopes that it may be of use for planning passage times etc.

NOAA Chart 25609: British Virgin Islands
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Old 30-06-2011, 06:44   #2
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Re: Chart Images NOAA 25609 BVI

Correction: The botton of the chart reads "Copyright 1996 by the United States Government. No copyright claimed under title 17 U.S.C." So it's not *that* old.

I am going to try stitching together other charts as time permits. The only processing I do is conversion from hi-res JPEG to lossless PNG, specification of 600DPI, and color reduction to 8 bits per pixed, 64 color limit in total. That makes the chart look crisper with a compressed size reduction of 3 fold.

ImageMagick requires about 12hours.
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Old 30-06-2011, 15:10   #3
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Re: Chart Images NOAA 25609 BVI

This chart is available from NOAA in the online viewer, here: Index of /NGAViewer/25609
You can reassemble any image from online viewer by using one of the "dezoomify" scripts.
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Old 30-06-2011, 20:54   #4
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Re: Chart Images NOAA 25609 BVI

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Originally Posted by brak View Post
This chart is available from NOAA in the online viewer, here: Index of /NGAViewer/25609
You can reassemble any image from online viewer by using one of the "dezoomify" scripts.
Thanks, yes indeed, that is where I found that chart. I wrote my own dezoomify script in ruby and imagemagick that achieves pretty good compression by reducing the colors to a depth of 64, though 128 is almost the same. In fact I think the chart looks better when the number of colors are reduced. Where can I find the script you mention? I may combine elements of it into mine, maybe set it on a slow churn and eventually bundle all the chart images. Perhaps these charts could be bundled into torrents.

I was googling for this chart months ago with no luck.
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Old 30-06-2011, 21:25   #5
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Re: Chart Images NOAA 25609 BVI

I think other than this chart, pretty much all NOAA raster charts are already available as BSB files. No need to reassemble when you can just download them ready-made

I am guessing this chart is not available as BSB because it is so severely out of date.

When encoded as BSB, chart images use indexed colors. I wouldn't change colors much, rather I would run it through some filtering and then into indexed color mode to get a small palette (less than 32 colors would be good).

Of course a set of modern updated UKHO vector charts for BVI costs something like $30 (probably raster too)
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Old 01-07-2011, 10:41   #6
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Re: Chart Images NOAA 25609 BVI

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Originally Posted by allanpeda View Post
Thanks, yes indeed, that is where I found that chart. I wrote my own dezoomify script in ruby and imagemagick that achieves pretty good compression by reducing the colors to a depth of 64, though 128 is almost the same. In fact I think the chart looks better when the number of colors are reduced. Where can I find the script you mention? I may combine elements of it into mine, maybe set it on a slow churn and eventually bundle all the chart images. Perhaps these charts could be bundled into torrents.

I was googling for this chart months ago with no luck.
Thanks for starting this thread, and thanks to Brak for pointing out the NGA chart resource.
I found two scripts that I'm testing.
A ruby script:http://https://gist.github.com/59636
And a Python script: http://http://commons.wikimedia.org/...s/dezoomify.py

I think we need the OpenCPN community in on this. It is very similar to but, much bigger than the NZ chart picture repository.
I'm starting a new thread over in the OpenCPN forum.
Thomas
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Old 07-09-2012, 10:14   #7
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Re: Chart Images NOAA 25609 BVI

Appears that NOAA no longer has chart 25609 in their catalog. Too bad.
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Old 12-03-2013, 13:24   #8
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Re: Chart Images NOAA 25609 BVI

Actually, the chart is a product of the National GeoSpatial Intelligence Agency site.

They can be found at

Digital Nautical Chart
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Old 13-03-2013, 14:55   #9
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Re: Chart Images NOAA 25609 BVI

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Originally Posted by morewind View Post
Actually, the chart is a product of the National GeoSpatial Intelligence Agency site.

They can be found at

Digital Nautical Chart
You just replied to a Sept 2012 reply to a July 2011 post. Old news.

The NGA does not have charts available to non-government users. Unless I am missing a change somewhere, you cannot download DNCs from that site. Only DNC updates, not the base charts.

The NGA DID erroneously have a large chart collection veiwable by the public but learned to their chagrin that enterprising open source people might decide to download them all. The entire collection was downloaded by a team on this forum and after a massive effort, managed to calibrate almost all of them and create BSB charts from them. But, then the NGA politely asked us to cease and desist because many of the charts were owned by other countries. Being polite and reasonable people, we complied with their wishes. Liking our freedom may, or may not, have played a part in that decision.

For details, see the ==> 1289 post thread here

-dan
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