Charts II: NGA - 2700 Charts

[HappySeagull]

Originally Posted by P_Dub

What is the full ftp site address for the finish product .kap file charts?
Regards
P_Dub

I actually don't know,myself P_Dub or even if there is one...I foresee the day when there might be one(and quite busy with constant downloads!..don't know who'll want to provide the bandwidth either!)

[recri]

Here are some chart corner coordinate examples for the manual:

The NE corner of 22082 specifies a longitude of 78d42'00.0" W, but the tick mark 12" west has the same label on it.

The NE corner of 61270 has a latitude of 8d55'00" N, but the corner label had a printing problem with the degrees.

There are no corner coordinates printed on 83495.

What to do in each case? I think the correct answer is fix the degrees on 61270, because it involves a repair to the most significant digit, and leave the other missing corner coordinates missing.

In any case, always leave a comment explaining what you did, and always note any errors or confusions in the charts in the comments.

[HappySeagull]

I think the correct answer is fix the degrees on 61270, because it  involves a repair to the most significant digit, and leave the other  missing corner coordinates missing.

I don't see why you'd leave it blank.Charts that have no corner positions written in can be figured out by just looking at the chart edge.It just takes a little longer than copying numbers.

[recri]

Originally Posted by HappySeagull

I think the correct answer is fix the degrees on 61270, because it  involves a repair to the most significant digit, and leave the other  missing corner coordinates missing.

I don't see why you'd leave it blank.Charts that have no corner positions written in can be figured out by just looking at the chart edge.It just takes a little longer than copying numbers.

First off, I didn't leave them blank I ended up filling them in, just like I tried to resolve the location of Puerto Morelos. But now I'm repenting, because some of them were harder to do, and some of the harder ones didn't turn out to be very convincing.

So on 61270 you could just read off the grid along the edge, and that would be fine. But on 22082 you have transfer a measurement across the chart to a marked grid.

Better to use other labeled points on the chart for georeferencing than to get into transferring measurements. If you supply a value that requires some work to come up with, then who ever wants to check it needs to do the same work.

[r.fairman]

I am guilty of calibrating chart no 54418 identified as having errors I checked the chart in OpenCPN and SeaClear and gave it the status of checked and locked. How to I go back in and correct my mistakes. Perhaps we should suspend the locking facility until recri has finished his error checking

Regards

An embarrassed Richard

[nohal]

Originally Posted by r.fairman

I am guilty of calibrating chart no 54418 identified as having errors I checked the chart in OpenCPN and SeaClear and gave it the status of checked and locked. How to I go back in and correct my mistakes. Perhaps we should suspend the locking facility until recri has finished his error checking

Regards

An embarrassed Richard

Richard,
unlocked the chart for you...
Just don't set this status yet, it's already turned on for the special cases when we need to do something manually in the database, that would be immediately lost if someone used the web form on the same chart.

Pavel

[bcn]

Originally Posted by recri

First off, I didn't leave them blank I ended up filling them in, just like I tried to resolve the location of Puerto Morelos. But now I'm repenting, because some of them were harder to do, and some of the harder ones didn't turn out to be very convincing.

So on 61270 you could just read off the grid along the edge, and that would be fine. But on 22082 you have transfer a measurement across the chart to a marked grid.

Better to use other labeled points on the chart for georeferencing than to get into transferring measurements. If you supply a value that requires some work to come up with, then who ever wants to check it needs to do the same work.

Recri,

I second this.
Typos should be corrected and if the data can be recovered without calculations we should do so as well.

Edit: when a method to generate PLYs comes up, that might be handy for those cases as well - giving Lat/Lon from pixels offsets from a know georeference

In any case a comment should be placed - recovering or not.

Is there a possibility to report the errors found to NGA?

Hubert

[cagney]

Originally Posted by bcn

Thomas, Pavel,

- the question of the hierarchy of chart types is still open.
If there is a 90 deg skewed chart which insets or corners out of range, how shall we categorize that chart: 90 deg skewed?

- rectangular charts with insets "on the water" are treated in non uniform way:
as "doable with insets" and as "special PLYs required"
Your idea?

Hubert

The way I see it, after a bit of "re"-thinking. Mind you, Nohal is the man actually doing the coding.

The categories are all just a help to prioritize the work. So as we just have one choice, I suggest that you pick them in this order. Note that this means that a chart may change status down the line.

1 If the corners are not visible, this must be fixed first. In odd cases this may mean manual calibration.

2 If the pic is skewed 90or 180, this must be done first before proceeding.

3 Next is inserts. I would imagine that Nohal/Gunther comes up with an interface to handle these. The result will be a "few" more "normal" charts to handle.

4 PLY adjustments. Some kind of interface. Maybe just a simple one where users can enter, the complete set of edited PLY:s. We have to issue special instructions exactly how to do this. It's not so difficult, but a bit time consuming and fiddly.

5 A few errors and adjustments will in the end not be worth while coding, and will need manual editing. The big category here is probably charts and insert plans without positions in the corners, and charts/plans with irregular shape.

Thomas

[bcn]

Thomas,

for me 90/180/270 degree would be the first to be categorized/resolved.

And as you observe, then the chart status has to be set to "zero" and the play rectangle/insets/missing corners/PLYs starts again.

BTW: what does "PLY" stand for?

Hubert

[nohal]

Originally Posted by bcn

Thomas,

for me 90/180/270 degree would be the first to be categorized/resolved.

And as you observe, then the chart status has to be set to "zero" and the play rectangle/insets/missing corners/PLYs starts again.

This one's easy, just takes some time, so I don't want to repeat it many times. I'm still waiting before doing it as there's enough charts left to process.

BTW: what does "PLY" stand for?

Hubert

PLY comes from polygon - it's the set of points (lat/lon pairs) defining the shape of the chart area (=what you see when quilting is on)
Solution is on the way. I expect to have it done today or tomorrow.

Pavel

[cagney]

Originally Posted by bcn

An updated version of the manual is available:

ftp://ftp.rr-consult.com.es

user: ftpuser
Pw: ftpuser

Thanks everybody for the suggestions!

Thanks for writing the documentation, very valuable.
For some reason, I can't reach your ftp address, might be a DNS issue with my ISP, so I have to wait for dacust...
I'll put a link to the documentation here: NGA Charts Status at OpenCPN.info (English)

A few notes.
Chart types. The "INTERNATIONAL" designation should be used for charts in the international IHO series. There is an INTXXX printed on the chart as well as the local NGA chart number. Almost all the charts concerned are in the "Region Miscellaneous". Typical example is Chart 10

Projection.
If no projection is stated, it s fairly safe to assume "Mercator", that is the way OpenCPN treats all charts that are not Transversal Mercator or Polyconic ,anyway. If the chart created passes the QA, then it is a Mercator.

Geodetic datum adjustment. It is a bit unfortunate that we can't enter values given in seconds, but have to first convert them to minutes of arc .We loose some accuracy that way. The reason for this, is that I had never seen this correction given in seconds when I advised (nohal/netsurfer) on how to treat these corrections.
Note that it is only corrections for WGS72/84 that should be entered here.

When is WGS, WGS 84 and when is it WGS 72?
The best answer I can find is that charts issued before June 28, 1994, should be designated WGS 72 and charts issued later should be called WGS 84. More details here National Geodetic Survey - Frequently Asked Questions

Thomas.

[kubek]

Hi,

I do two maps 44461 & 44430,
but I see think that I mark it incorrectly
as "Chart done, checked and locked"
but I see that most of the maps have status
"Rectangular, doable in Phase 1"
I have downloaded this maps and I've checked it
with OpenCPN and it's looks fine.

Could You unlock this maps that more people can verify it.

Best regards,

Pawel.

P.S. I try to do more maps in my region but I cannot set all REF point,
because one of margin is to big and tool cannot allow to set it correctly.
See map 44465 - upper margin.

[bcn]

Originally Posted by kubek

Hi,

.......
P.S. I try to do more maps in my region but I cannot set all REF point,
because one of margin is to big and tool cannot allow to set it correctly.
See map 44465 - upper margin.

Pavel,

please put as Chart status "Rectangular, not doable in Phase 1 because the corners are not visible on cutouts" in this case. There quite a lot of those type of charts that will be tackled later on.
Please enter the rest of the values despite of the status. It helps to advance the process for the future.

Hubert

[nohal]

Originally Posted by cagney

Thanks for writing the documentation, very valuable.
For some reason, I can't reach your ftp address, might be a DNS issue with my ISP, so I have to wait for dacust...
I'll put a link to the documentation here: NGA Charts Status at OpenCPN.info (English)

The latest version is also at https://github.com/ngacharts/ngacharts/downloads

Pavel

[bcn]

Originally Posted by nohal

This one's easy, just takes some time, so I don't want to repeat it many times. I'm still waiting before doing it as there's enough charts left to process.

Pavel

Great,

in Region 5 all skewed charts should be identified now.

Hubert