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Old 02-13-2011, 08:56 PM   #15
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By the way, is there a particular digital chart brand/system which is more accurate for the Pacific islands, in particular those farther from the beaten track? I suspect not, but would welcome opinions from people who´ve been using that kind of stuff there.

Thanks,

José Truda & Nalu
I don't know the answer to that one. I suspect that, as SeaVenture noted, the digital charts are only as good as the paper charts and would expect that to mean that if a reef is missing or in the wrong location it will be the same for all chart programs. Hopefully someone else can opine on this shortly.

Fair winds,
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Old 02-13-2011, 09:43 PM   #16
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Well, the answer to that one is yes and no.

Yes, they can be as good as the official paper charts and, in some cases, are simply the scanned version of the official charts. However, they can contain errors that the official charts do not have. Unless the chart maker has access to his own surveys the digital charts can never be better than the official ones.

What digital charts can do is programme in the WGS 84 offset so in thhat respect they are easier to work with than some paper charts.

Aye // Stephen
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Old 02-14-2011, 11:21 AM   #17
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Many thanks for your comments! Seems there´s a consensus on digital charts x paper charts being more an issue of user common sense than trust in accuracy.

Cheers,

José & Nalu
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Old 02-18-2011, 04:26 PM   #18
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No matter what: official paper charts are best concidering the point of actuality at low costs.

Meanwile it is no problem any more to get up to date *chart correction services offered by almost all national hydrografic offices online and for free.*

Well, it takes some time to apply the chart corrections on a chart that is outdated for, let's say 4 years, but with a little patience it should be accomplished. But most or us can not correct a digital chart this easy (maybe computer/programming gigs can...).

And except in tidal swept wadden seas with a fast change in topography and when major man made changes in water ways took place, the number of changes per chart are not as much as to keep charts updated over many years. *It's just *for example loading down the last weekly

notices to mariners

*- here I chose the UKHO, as they still cover alot ouf our planet, even the Pacific as far as it is covered by the British Admirality charts. (Click on WEEKLY and just choose *a pdf and select/download a week's content!).*

I was not yet in the need of the correction services by other major hydrografic servics in the Pacific area, but *there are *similar services in * * *Australia * , * NZ* , Japan and maybe other nations. *

So, with some patience and time *it is no problem at all to have up to date paper charts world wide. Download the free pdf s, draw/write the small changes into your chart (like new lighting characters of buoys) or print out the small chartlets with the more complex changes and glew them into your chart. If using a laser printer the correction is even as water resistant, as paper charts can be.*

Uwe

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Old 03-21-2011, 01:14 PM   #19
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On the subject of chart errors and accuracy, some of you may be interested in the TeamSurv project (www.teamsurv.com).

This is a crowd sourcing project to create more up to date and accurate charts, using depth and GPS data logged by boats.

Using a hardware or software data logger, you collect data whilst doing your normal sailing activities, then upload the data to the web. There, tide height and other corrections are applied, and you can see the results online.

We are just proceeding to the next stage, where charts will be available for download in areas where we have sufficient data.
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Old 03-21-2011, 06:17 PM   #20
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On the subject of chart errors and accuracy, some of you may be interested in the TeamSurv project (www.teamsurv.com).

This is a crowd sourcing project to create more up to date and accurate charts, using depth and GPS data logged by boats.

Using a hardware or software data logger, you collect data whilst doing your normal sailing activities, then upload the data to the web. There, tide height and other corrections are applied, and you can see the results online.

We are just proceeding to the next stage, where charts will be available for download in areas where we have sufficient data.
Cloud sourcing and cloud data is all very interesting. However, the result is going to have a great deal of uncertainty in it. Given enough data in a particular location, you will have a reasonable picture of what is going on. However, it will take huge numbers of data points to get a chart reliable enough for use in navigation.

What sort of corrections to GPS data? Are you collecting which GPS system and what triangulation/sat's are in play when the data is being collected? Depth--how will you actually know that the boater is providing you with accurate depth information rather than simply depth below the transducer?

Again, cloud sourcing is a wonderful way to get large and helpful/useful datasets. It isn't necessarily a good way to pin point something with accuracy or precision.
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Old 03-21-2011, 08:09 PM   #21
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Cloud sourcing and cloud data is all very interesting. However, the result is going to have a great deal of uncertainty in it. Given enough data in a particular location, you will have a reasonable picture of what is going on. However, it will take huge numbers of data points to get a chart reliable enough for use in navigation.

What sort of corrections to GPS data? Are you collecting which GPS system and what triangulation/sat's are in play when the data is being collected? Depth--how will you actually know that the boater is providing you with accurate depth information rather than simply depth below the transducer?

Again, cloud sourcing is a wonderful way to get large and helpful/useful datasets. It isn't necessarily a good way to pin point something with accuracy or precision.
It seems to me that this is a good way to find places where more than usual caution is required. If you have a series of hints that a rock may be a mile north-east of it's charted location, for example, you may choose to take all chart data near it as a hint rather than a fact.

OTOH, a health mistrust of charts is a good idea lots of times anyway.

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Old 03-22-2011, 01:27 AM   #22
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That series of hints if it came via GPS may simply be an indicator that the GPS datum isn't quite right for the location you're cruising in. If you cruise exclusively using GPS, well then indicators that GPS is "off" in a particular area is good to know.

I have a "healthy mistrust" of people's ability to navigate using GPS. Oftentimes, we are shown via GPS to be quite a distance away from known visible things that I can see: shoreline (GPS has shown me sailing along ON shore many times), channel marker, rock, etc.

What is better, IMHO, is to become good with the paper charts and dead reckoning. But hey, that's just me.
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Old 03-22-2011, 05:16 PM   #23
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...

What is better, IMHO, is to become good with the paper charts and dead reckoning.**But hey, that's just me.
You are perfectly right and not alone!

This is what we love about sailing: doing the navigation work on real paper charts.

We don't even have a GPS street navigator in our car!

Uwe

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