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Old 07-09-2012, 16:17   #1
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Resolution of Soundings in Vector Chart

Hi,

I'm a new user of OpenCPN (v. 3.0.2 on a Macintosh) and this is my first post.

I'm wondering if there is any way to round the decimal part of soundings in a vector chart. Decimal parts of a foot is way more resolution than I need and they make soundings hard to read.

I've attached a screenshot to show what I'm talking about (hope this works). Look at the soundings near the shore and you'll see values like "0.9" feet (although displayed in an idiosyncratic fashion: the decimal part is shown as a subscript on the whole number part). Is there any way to round this to "1", for example?

David
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Old 11-09-2012, 01:18   #2
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Re: Resolution of Soundings in Vector Chart

Quote:
Originally Posted by davidfay View Post
Hi,

I'm a new user of OpenCPN (v. 3.0.2 on a Macintosh) and this is my first post.

I'm wondering if there is any way to round the decimal part of soundings in a vector chart. Decimal parts of a foot is way more resolution than I need and they make soundings hard to read.

I've attached a screenshot to show what I'm talking about (hope this works). Look at the soundings near the shore and you'll see values like "0.9" feet (although displayed in an idiosyncratic fashion: the decimal part is shown as a subscript on the whole number part). Is there any way to round this to "1", for example?

David
Welcome aboard, David

There is nothing idiosyncratic about the way these soundings are displayed. There is a single official internationally recognized way to do it. Have a look at any textbook covering chart reading.
Rounding ? Who would tinker with the values given by some official hydrographic institution ? I wouldn't, 'cause I can't offer the lawyers' fees in case someone runs aground....
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Old 11-09-2012, 15:11   #3
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Perhaps the right answer is: if you don't care about soundings just turn them off (eg using the cool "s" shortcut coming in 3.2) to de-clutter the display. And if you care about them: the more accurate the better!
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Old 11-09-2012, 15:33   #4
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Re: Resolution of Soundings in Vector Chart

In theory all the data associated with vector charts is stored as data, and in theory it should be a trivial exercise for someone familiar with the chart format to extract the depths, round then (down, the next next shallowest whole foot for safety's sake) and then reload a modified chart with that data.

I expect the liability concerns would prevent any vendor from doing that, but in theory, the modification should be a piece of cake.
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Old 11-09-2012, 16:38   #5
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Re: Resolution of Soundings in Vector Chart

What confuses me is that BSB charts from the same area don't show decimal fractions for the soundings. I assume both are made from the same underlying data. That is, only one set of soundings exist for any given area. So if BSB charts are rounding the underlying data, why don't ENC charts do the same?

Obviously, there's lots I don't understand about charts. Maybe it's time for me to read Nigel Calder's "How to Read a Nautical Chart".

David
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Old 11-09-2012, 18:08   #6
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Re: Resolution of Soundings in Vector Chart

"So if BSB charts are rounding the underlying data, why don't ENC charts do the same?"

BSB charts are raster charts. That is, "paintings".
ENC charts are layers of data, vector charts that are plotted and presented on your screen in real time, subject to filtering rules. That's why you can display an ENC chart with "everything less than 10 feet, show as red" and make it happen. There are pros and cons to each. For instance, a BNB chart will show feet or meters or fathoms, whatever it was drawn with. And ENC chart will have the water depth encoded in the data, but given good software, you can display it in feet, meters, fathoms, or millimeters as you prefer. Which might require rounding errors or decimal points, again depending on software options. Remember, "you" are creating the ENC chart that you see to a large extent. You can make wrecks, cable crossings, bottom types, appear and disappear. Can't do that on a BNB raster chart, unless you've brought along the digital white-out. <G>

"How to read a nautical chart" or even the old "Chart Number One" will tell you how to read a chart, but I don't think either will tell you about the practical differences between raster and vector charting.
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Old 11-09-2012, 19:17   #7
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Re: Resolution of Soundings in Vector Chart

Actually, "How to Read a Nautical Chart" is very helpful -- it has lots of information on how paper, rasterized and vector charts are created. I haven't found an explicit discussion of why a raster chart would show, for example, 2 for a sounding while the vector chart would show 1.9 for the same sounding. But it has some hints.

Apparently, some modern paper charts are made from data collected in "vector format" (by that, I suppose Calder means "digital"). That same data can also be used to create a vector chart. Thus it's possible for the paper chart maker to decide to round the soundings to whole numbers while the vector chart maker makes a different decision.

David
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Old 11-09-2012, 21:19   #8
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Re: Resolution of Soundings in Vector Chart

The paper chart maker chooses and fixes information before it hits the paper.

The vector chart "maker" is actually the software that the user has chosen, set to the parameters the user has chosen, and subject to the limits of the vector data sets from the supplier.

It's the difference between buying a recording, and hiring a live band.
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Old 12-09-2012, 01:56   #9
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Yes vector is far superior and is the chosen method for IMO ECDIS on large ships.

Dave
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