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Old 20-07-2006, 04:34   #16
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The satellite images I use have about 30 calibration points, and have been fine in comparison with the chart so far!
Having been in the land based map making business using aerial photos I can tell you that close is OK for what it is but it's not the same. 30 calibration points can't remove the distortion. The space between the calibration points is about as bad as it was before.

The idea that you could use a digital camera to scan charts is probably worse.
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Old 20-07-2006, 12:40   #17
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In the days before GPS we used to reckon a fix that was within a couple of hundred yds was good, now if it isnt pin point accuracy we complain!
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Old 20-07-2006, 13:44   #18
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Originally Posted by Pblais
The idea that you could use a digital camera to scan charts is probably worse.
Why? What problems could I possibly be missing? Why is a carefully calibrated camera setup different from a scanner? Other than being more of a pain in the butt of course
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Old 20-07-2006, 16:12   #19
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Originally Posted by Chris31415
Have you tried taking your setup out in your boat in an area that you know well (in good weather!) and trying it out?
I have. Since I am still in USA waters and all of the local charts are freely downloadable, I have done it as a test, but I haven't found any serious problems.

On the charts I have carefully checked I find a maximum error between the calibrated value indicated by the cursor and the underlying image of about 0.2 seconds or about 200 feet. (60 meters) on the largest harbor scale charts. On offshore scale sharts the error is proportionally similar, but, of course, larger in absolute terms.

For me this is quite good enough, and of the same order of uncertainty I would get in transfering a reading from a GPS to a paper chart. For someone who uses their chart program to dock their boat, it might not work

It may be that the argument is all over how good is good enough. I use my computer like I use papercharts. It's not in the cockpit and is used to plan, track, and log. We never steer the boat watching the screen like a video game.
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Old 21-07-2006, 02:59   #20
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Why would you want to introduce another small, indeterminable, error into the equation.

Navigational and steering errors are cumulative, and each small error will add (vectorially*) to become a larger, and difficult** to predict, total resultant error.

*Vectors are quantities which include a direction.
**The difficulty arises in calculating (trigonometrically) resultants from imprecise vectors, where neither the exact magnitude (quantity) and direction (angle) are precisely known.

Of course, I often use hand-drawn Sketch Charts, and “basic visual” piloting. I suppose I’m just being anal and argumentative ...
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Old 21-07-2006, 05:03   #21
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For me this is quite good enough, and of the same order of uncertainty I would get in transfering a reading from a GPS to a paper chart. For someone who uses their chart program to dock their boat, it might not work
What waters do you sail with these charts? Given you don't really use them in US waters it sort of makes the case that you wouldn't use them if you did niot have to.

The biggest error you will get is the error of tilt, radial distortion of the lens plus the imprecission of the digital focus. You can"generally" calibrate it but you can not remove those errors. You only move them around in tniy hideous ways. Where you calibrate can appear pretty good but what about the rest?

Now if you take the US chart for the eastern Pacific and calibrate the center of the Golden Gate Bridge and Cape Kumukahi. I'mll bet you could draw it by eye on the back of a napkin and go to Hawii and back no problem. I just wonder if you could hit San Deigo without calibrating Point Loma too. Large scal small scale same problem.

They don't make charts by optical reproduction any more for about the best reason I can think of - they don't have to. With a lot of training you might be able to sail around the world with the same maps Magellan had but even he would have taken a better map if he could get one. He took a few sea chests full of navigation gear.

Even the reduced scale chart books that Maptech sells are not made from optical reductions of paper charts. They make the master direct from the original digital data and load it directly to the printing press. All the work is done starting from orginal source materials.

It's one thing to pretend they work with charts you don't rreally neeed to use but why would you spend the many hours required to reprocuse the many charts you would eventually need for a long voyage. How many times might you screw up the calibration?

As Gord notes I too use hand drawn sketches (the Chesapeake Bay Guide has tons of them and are very valuable) to access difficult find anchorages but always in conjunction of a real chart. Sometikmes the tiny details of the chart make a difference in ways you can not foresee until you get there or someone tells you with a sketch. It's more than just a lot of way points. There are all the other places you may not intend to go but end up in that matter alot too.

There really is no reason not to take the best charts you can obtain and learn the skills to use them well.
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Old 21-07-2006, 10:52   #22
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I think in their enthusiasm to critique the scanning process I have used, people missed the point of my post. I use paper charts as my primary navigation tool.

As I pointed out in the beginning of the thread (which people commenting on recent messages seem to have not read) I insist on having a FULL set of paper charts on board. These are my PRIMARY navigation tool, and I just do not see the value of double spending (at least!) for a full set of electronic charts for an extended cruise through Central America and the South Pacific. Computer hardware is relegated entirely to what the military would call "non-mission critical uses".

On the other hand, if my sailing was to continue to be restricted just to San Francisco Bay and it local environs I would probably be all electronic with a set of paper charts moldering in the depths of the bilge "just in case".

By keeping my eyes and ears open I have been collecting used original charts of the planned cruising areas for US$4 to US$6. I can fill in any blanks with large format commercial photocopies for on the order of US$9. I am not going to spend thousands of extra dollars to buy a set of electronic charts for the area I intend to cruise, that's too big a chunk of the cruising kitty. I learned to navigate on paper, I enjoy and prefer using paper. And yes, I do have a sextant on board and know how to use it.

Do not forget, in many places around the world the registration between the charts and any known GPS datum is a bit dicey, at best. We are truly spoiled here where my GPS can literally tell me what pier of the marina I am docked at.

Finally, here is the rule I use for what is required to take with me on long cruises: If I was in a remote anchorage and the device in question failed, would I consider myself stranded there until a replacement could be obtained? If my paper charts disappeared I'd find a way to replace them before heading out on the ocean. If I lost all capability for making a GPS fix, I'd replace it when it was convenient. If my computer/chartplotter died, I'd sail on and not miss it very much.

And I promise; I’ll write nothing else in this thread, so if you want the last word, have at it!
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Old 22-07-2006, 00:27   #23
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I'm with you. Anything to make navigation cheaper and easier.
I cannot see how scanned and corrected charts could be any less accurate than the old paper charts.
Go for it.
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Old 07-08-2006, 16:17   #24
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I have a coughpiratedcough copy of Cmaps ECS (that seems particularly ubiquitous amongst the budget conscious yachties). I run it on a cheap laptop on-board, but I also have it loaded onto a desktop PC. I often make myself "deck charts" (i.e charts that I can use on deck so that I don't need to go below) by setting my screen resolution to maximum, and taking "print-screens" which I can dump into a standard paint package and then print at A3, and laminate. This makes a handy, waterproof chart that you can even draw on with a fiber-tip pen.
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Old 07-08-2006, 17:23   #25
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I think you have a quite functional system, though RayMarine let go the format because it was easy to pirate. Actually VERY easy. It's why it no longer really acknowledges that the old C-Map format exists.

Personally I like digital maps with 8 1/2 X 11 deck copies myself. They are good enough to plot on for most purposes.
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Old 07-08-2006, 18:02   #26
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Laminated is good, if you use them often enough and have a laminator around. But there are also synthetic "papers" made of Tyvek and latex especially for inkjets (and some for lasers as well) that are great for damp use. The ink is always another question <G> but cheap hair spray makes a good lacquer coat too.
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Old 08-08-2006, 03:05   #27
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I have seen the old C-Map ECS and although I liked the charts, the plotter was very basic. However, If you can "purchase" a copy of Maxsea version 10 (preferably 10.3) this overcomes some of the worst aspects of the C-Map (including that irritating need to go to 128 colours).
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Old 08-08-2006, 18:07   #28
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Quote:
Originally Posted by GreatKetch
Are there any navigation programs other than the free-ware SeaClear (www.seaclear.net) that allow you to use self-scanned papercharts in electronic navigation?

I am (slowly) being dragged into the 21st century by the benefits of computer aided navigation, but INSIST on paper charts on board. Right now there seem to be three ways of doing it:

* Buying a full set of paper charts AND a full set of electronic charts. Very Expensive!
How about buying paper backup charts for selected locations along the way? You don't need every chart and there could be a cost savings. The only problem is when you electronic chart system dies. Pencils and paper always work. How about swapping charts or buying used ones?

Quote:
* Buying a full set of electronic charts and printing them all out. Time consuming and still not cheap, and without a big and expensive printer, you end up with marginal paper copies.
Size and image accuracy would be a prime problem. There is no way to verify that your printer/program will reproduce exactly what the chart contains to the ppi accuracy you may need unless you can do a one-on-one comparison before leaving. You're also stuck with a huge printer, the requirement to stock paper for your printer (not all stores outside where you live may stock paper you use - e.g. US letter is not the same as A4) and another power and storage hog. Finally, there is the problem of moisture. You'd have to seriously consider water-tolerant paper and inks and the cost/sheet is way above the bulk paper prices you're probably thinking about.

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* Buying a full set of paper charts and scanning them in to the computer. Time consuming and cheap(er).
The smallest charts I've seen that I'd even consider using are 24x30" and the largest are 34x46". To my knowledge I know of no pro/consumer scanner that would scan the entire image. That means you must overlap and then stitch the images together into one large image, convert it to a format that's acceptable to your chart software, and then verify that the import is 100% complete. That means playing with scanning resolutions, depths of color, and other factors. Then you have to decide if the file size is something you and your system can work with.Way too much work and possiblity of error for a few dollars saved.

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I have had good success "scanning" charts with my high-end digital camera. Am I missing something an alternative?
For my circumnavigation I'm looking at paper charts, guides, and electronic charts. The further you go afield, the higher the costs to travel there. I grumbe when the best chart for an area is USD40 and current (WGS84) as opposed to a 4th-generation photocopy of a survey made in 1849. But I have a far better sense of security knowing the data presented is more accurate. And I rejoice when I can get Admiralty chart photocopies for a few dollars. I am not a fan of B&W charts and have spent days coloring land and shallow water areas in with colored pencil.

I'd consider finding additional charts for the next area your heading a priority. I've been able to borrow current versions of guides, and for the cost of dinner and comradery, update my older ones to reflect the latest changes. I've found out-of-print charts and guides at book swaps or from other sailors. I've even borrowed guides and had the relevant sections photocopied so I'd have additional information. I belong to SSCA and their monthly Commordores Bulletins is about as current as it gets. I have the last 6 years on CD and I can use that as a reference. Areas you may be considering may have charterboat operations and they usually have a good guide of places to go.

My $0.02 worth: navigation references are too important to drop too far down the cost/item list. Pay the money, get what makes you the most secure, work another month, or shorten your cruise.

Doug
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Old 22-10-2006, 22:54   #29
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Fugawi can upload scanned maps and calibrate them. Take a look at their website: http://www.fugawi.com/web/

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Old 28-10-2006, 13:05   #30
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I don't understand. You'll pay one quarter of a million dollars for a boat, but want the cheapest navigational tools to protect you and it. Do you also use old tires for fenders and polypropylene line from Wal-Mart?
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