Charts II: NGA - 2700 Charts

[paulr]

Here's a type of input error to watch out for:

chart 82356

Soundings datum entered as
MHHW instead of LAT.

Not yet corrected.

[Tia Bu]

Originally Posted by paulr

Absolutely no doubt that this is a useful way of checking, but I would like to sound a note of caution. All the charts need checking manually too, and, I suggest, by at least one person other than the original calibrator.

I have found quite a few errors that cannot be picked up by computation, but which could have a serious impact on the credibility of the project.
54418 mentioned above is a case in point. The soundings datum is set to MHWS, not MLWS. Just by random checking, I've found and corrected half a dozen or more incorrectly specified soundings datums.

Whatever warnings we attach to these charts, people are still going to use them for navigation. Specifying fathoms instead of metres, for example, could have very serious consequences.

Paul

You're right, of course. But all of us who are working on this project can learn a lesson ourselves as navigators. I've been navigating boats in the ocean for 35 years now, I guess, and I've learned more about international charts from this one exercise than I ever knew: mainly-- they're UNRELIABLE! They need to be double, triple checked. Your assumptions as a navigator need to be questioned, tested, and double-checked. And you should never cut it close!

Of course, I've already left enough keel filings and bottom paint on enough reefs and sandbars all over half a hemisphere to have learned that lesson before. I just keep forgetting it. When that little red boat starts gliding over these shiny NGA charts on my computer screen, I bet I'll forget it again.

By the way, the charts themselves already have a good warning in red that we all ignore at our peril-- even in the GPS and computer chart plotter age.

[sinbad7]

Well said TiaBu.. it is the summa summarium of all kinds of situation information we receive which paints the final picture we scrutinize with a good deal of suspicion,allowing ample leeway.

Tore

[cagney]

Originally Posted by paulr

Here's a type of input error to watch out for:

chart 82356

Soundings datum entered as
MHHW instead of LAT.

Not yet corrected.

Thank for keeping your eyes open!
What you're doing is actually part of the open source quality check
Errors in sounding datums could actually be picked up by a script searching for an "H", which would raise a red flag and warrant manual checking.
Quite a few of the choices for sounding datums, should never have been there in the first place!
Many checks can be done using the status page just scanning down the different columns etc.
But you are right, we do need a lot of checks before any kind of release.
We are not even at a beta test stage yet!
After sifting through and correcting a few charts in the "other" category, I'm fully aware of errors and different judgments in details.
But as always, it's easier to detect others mistakes, than your own.
Just look at all the errors we find in the NGA charts themselves.

Thanks, and keep looking for, and correcting errors!

Thomas

[bcn]

Originally Posted by paulr

I have found quite a few errors that cannot be picked up by computation, but which could have a serious impact on the credibility of the project.
54418 mentioned above is a case in point. The soundings datum is set to MHWS, not MLWS. Just by random checking, I've found and corrected half a dozen or more incorrectly specified soundings datums
Paul

Paul,

thanks for the corrections. It's obvious that the inputs should be double-read and checked.
The datum for soundings is perhaps the most confusing concept I've found. No datum in a lot of cases. Other where you have to guess which concept is meant. Then it is very easy just to commit an error in the drop-down box (glasses on/off).

The question is how to implement a second view/check on the data submitted. Up yo now we don't have "check-box" to indicate that pass.

Keep your eyes open, please - and shout on us if necessary!

Hubert

[bcn]

Thomas,

if you - or anybody else as well - have examples or comments how to do it right or what to avoid, please publish the examples/experiences/learnings.

Originally Posted by cagney

Thank for keeping your eyes open!

After sifting through and correcting a few charts in the "other" category, I'm fully aware of errors and different judgments in details.

I will start in the next days with the next release for the manual - inputs are very welcome.

Call for a writer of a glossary to be included!

Hubert

[wdkester]

I have never worked on a project like this before. However, in a previous life, I looked at engineering drawings. The creator of the drawing signed and dated the drawing, any modifications were signed and dated, and finally a manager signed off on the drawing for production. Could we do a simple version of this. If we're worried about liability, perhaps the final check off destroys all initials.

[recri]

A colorful index to the complete NOAA/NGA chart catalog.

Current Nautical Charts: Main Index

I didn't realize that the NOAA US chart set drops right into the same numbering scheme.

[Doek]

Hi Guys, I am now free to work on these charts as well. Do you need any help and where do I start? Is there a specific post that describes the procedure that works best at this point in time?
Don

[bcn]

Originally Posted by quackedo

Hi Guys, I am now free to work on these charts as well. Do you need any help and where do I start? Is there a specific post that describes the procedure that works best at this point in time?
Don

Great Don,

welcome on board!

Please have a look at
NGA Charts Status at OpenCPN.info (English)

Here you will find the actual manual for calibrators (a beta version as the whole process).
Region 7 and 9 are those that might need a helping hand.
And checking the already done charts is also an important task.

The NZ part of Region 7 is very well covered by a different project already.

And with any questions or doubts please come back to the list!

Hubert

[Viking Sailor]

Originally Posted by recri

A colorful index to the complete NOAA/NGA chart catalog.

Current Nautical Charts: Main Index

I didn't realize that the NOAA US chart set drops right into the same numbering scheme.

Firstly, a very well earned thank you to everyone who has helped in the NGA chart conversion effort. This is truly an amazing accomplishment.

The above quoted post illustrates the fact that the NOAA/NGA charts are organized for use as paper charts. This has been bothering me for sometime. Here are some thoughts that I hope will be helpful if it is determined that a better way to organize these charts for use with OpenCPN is needed.

As an example of charts organized for use in a electronic chart display system are the CM93 charts. These charts are organized in a hierarchal file structure by latitude and longitude. This allows OpenCPN to display the charts with a minimum of processing.

It seems to me that there are several ways to accomplish the reorganization of the NOAA/NGA charts.

One way would be the direct route where the charts are renamed in a way similar to the CM93 charts. This would require a complicated chart updating process where a single .kap file may need to be copied into several locations in the file structure.

Another, would be to make a CM93 like file structure with pointers or links to the appropriate charts. This method would require a lot of inefficiently used disk storage and a lot of extra disk accesses.

Perhaps the simplest way would be to just create a text file of the CM93 like file structure with relative links to the NOAA/NGA charts that could be loaded into memory. This text file would be located in the same directory as the .kap files. This last method would minimizes disk storage, chart database processing, and simplify the chart updating process.

Again, thank you one and all.

Paul

[HappySeagull]

Originally Posted by bcn

Thomas,

if you - or anybody else as well - have examples or comments how to do it right or what to avoid, please publish the examples/experiences/learnings.




I will start in the next days with the next release for the manual - inputs are very welcome.

Call for a writer of a glossary to be included!

Hubert

Question..
looking at the manual,(at least the one I'm looking at)I don't see what the user would do with a datum "WGS" as it's not in the drop down list....but it's very common on the charts.
My answer=WGS84.
Reason:as I've seen it,WGS=WGS84.

"Adindan"
for one source...also given GPS accuracy anyways

[HappySeagull]

...that said,a cool tool is GeoTrans2,also available from the NGA..."Geodetic" is your easiest way-in as opposed to "Mercator"

[wdkester]

Chart 26128 Kingston Harbor. Opencpn's Long. grid lines don't match the chart. I believe that the corner marks for long. are about 0.5" off This is an error of abt 30mtrs. Not much, but this is a harbor chart. So? For my own use, if I thot that I were going to Kingston, I would "correct" the chart in my files.

I added a comment noting the error in the database.

[Tia Bu]

Hey guys:

I was just working on the charts. I changed a few charts that somebody else started. And I noticed some folks have changed a few charts that I previously started (and some I previously had "finished").

And in all those cases, the changes seem to have improved the product.

It occurs to me that what we may have inadvertently begun building here is a chart Wiki. Is that where this project ought to wind up going? Studies show that Wikipedia is more accurate than Encyclopedia Brittanica, even though anybody in the world can change Wikipedia anytime they want to. Could we end up with a site that allows people to append these charts with up-to-date soundings, updates from Notices to Mariners, and other data gathered in the field?

Then the warning on the charts might be-- hey, this is a Wiki chart from a group Internet effort. Be careful! Use it wisely.

Would that be more valuable in the long run? I kind of get the feeling that we're giving some of these charts more careful attention than they've gotten in a long time.

Just a (very) half-baked thought. For what it's worth.