Charts II: NGA - 2700 Charts

[recri]

A link on the stats page, NGA Charts project stats, that puts all the charts, irrespective of status or region, on one page would be helpful.

Some of the missing corner charts turned out to be a parsing error, but these charts:

25570 28201 29126 37166 44082 51261 51461 52060 52082 52164 52170 52281 53089 53130 53141 53201 53283 53302

are really missing corners. They probably have corners which aren't on the cutouts but the charts got marked as Rectangular, doable in phase 1.

[wdkester]

Originally Posted by recri

I processed the 489 charts in the Rectangular, Doable category about an hour ago.

I discarded all the charts with less than 5 digits in their chart numbers, all the charts which weren't MERCATOR, all the charts with missing corner coordinates, and computed the nautical miles/pixel ratio as described above.

There were 433 charts which were "square" to better than 9 parts per thousand, the ratio was greater than 0.991 and less than 1.009. The mean for those charts was 1.00436 with standard deviation of 0.00208.

I inspected all the charts outside the cutoff.

These 7 charts, all high latitude large scale, appear to be correct:

29002 29025 35000 37000 42046 43015 44000

These charts all have errors in corner coordinates:

24400 25400 44069 51002 51400 51460 52054 52262 53244 53281 71005 74002 81151

There are several places where 0, 6, and 9 got confused, there's one with the same longitude for east and west, and a couple where east ended up west of west or south north of north.

Great job recri, 24400 and 24500 have been corrected.

[recri]

Originally Posted by siff

To help somewhat, there is a pdf catalog of the charts for each region which shows the subsets. I found the region 2 at this place, but they are certainly somewhere on the nga site. It could be fine to put a link or a copy of them on the general nga status page

The catalog is very useful, in fact I need to go look at it now.

But the issue with region 2 is that every time you reload the region index to see if a new kap has been generated, the page has to load 618 other chart records before it refreshes to the location you're looking at. Breaking it into subpages with fewer charts would make subpages that loaded faster and generated less server load.

[recri]

I'm struggling to learn with 28201 - Puerto Morelos (Mexico).

It was one of the missing corner coordinate charts in region 2. Someone noted that it was in the wrong place and gave a rough correction but didn't enter much else.

So I entered the rest of the data, and it was in the wrong place. I applied the correction suggested by the commenter, and it's still in the wrong place.

There's a light at Puerto Morelos, but the next larger chart is 27120 - Yucatan Channel and it's way larger -- we're going from 1:18050 to 1:350000 -- so it's really hard to believe that they're lined up.

I really wish that opencpn could fade between chart resolutions. The charts at GeoGarage - Home fade between chart and google satellite imagery and I really like seeing how things match up. But I also get the impression that option requests for opencpn play a zero-sum game with our charting endeavor, so forget I wished for that.

So I guess the best thing to do is to lay down a route in opencpn along the coast at 1:18050, with a detour to the marked light, and then see how that route looks at 1:350000, and see if I can deduce the remaining correction. Or maybe decide that there is no further correction that can be justified given the charts I have.

[bcn]

Recri,

this is a really big help!

Originally Posted by recri

I processed the 489 charts in the Rectangular, Doable category about an hour ago.


These charts all have errors in corner coordinates:

.... 51002 51400 51460 52054 52262 53244 53281 .....

The values are now corrected but one: 53281 - there I have not found any error.
Perhaps somebody more should have a look on it too.

Hubert

[bcn]

Originally Posted by recri

A link on the stats page, NGA Charts project stats, that puts all the charts, irrespective of status or region, on one page would be helpful.

Some of the missing corner charts turned out to be a parsing error, but these charts:
... 51261 51461 52060 52082 52164 52170 52281 53089 53130 53141 53201 53283 53302 ....

are really missing corners. They probably have corners which aren't on the cutouts but the charts got marked as Rectangular, doable in phase 1.

This is right and it would be possible to get the missing corners working with GIMP. But as we are with a general problem (in the case of the charts I had a look on we are talking about 10% of the total) I would like to wait for a solution that is valid for everybody.

In the case corners/PLYs are missing there is a comment placed in the chart data.

Hubert

[paulr]

Originally Posted by recri

I'm struggling to learn with 28201 - Puerto Morelos (Mexico).

It was one of the missing corner coordinate charts in region 2. Someone noted that it was in the wrong place and gave a rough correction but didn't enter much else.

So I entered the rest of the data, and it was in the wrong place. I applied the correction suggested by the commenter, and it's still in the wrong place.

I don't know how others feel about this, but my understanding is that the work we are doing here should be replicable and verifiable by reference to the chart.

I would have thought that that exempts entering data from external sources.

If the chart has no datum note on it, then I expect to see "No DATUM NOTE given on chart" ticked.

How will we know what to do and why, when, for example, the chart is repulled from NGA because they have rescanned it and we want to recalibrate it?

Paul

[bcn]

Paul,

completely agree.

Maintenance is an open point for sure. And a difficult one in a community project. One can volunteer to nurse a range of charts, but obviously we can't avoid that somebody gets tired about it or disappears.

Charts re-loaded or updated should be highlighted perhaps.

Hubert

[paulr]

1. Is there a hierarchy of non-doable statuses? Setting the right status might facilitate the next phase. For instance, how to classify a 90-degree skewed chart, with non-visible cutouts, and consisting of non-rectangular charts? Is it better to classify it as 'non-rectangular charts' so it gets shunted to the back of the queue, or as '90-degree skewed', so that it at least gets deskewed early on (on the assumption that deskewing is next in line)?

2. The Soundings datum dropdown has a slightly annoying 21 items in it, so it has to scroll by one item. I imagine this may be browser-defined. Given that, could we perhaps add a few other abbreviations (or the full text) of datums that there are a reasonable number of: Indian Spring(s) Low Water, Equinoctial Spring Low Water

3. It's still early days, but it will soon be useful to be able to filter the Region status pages, to hide/show only the completed ones, to show only the untouched ones, etc. Is that on the cards?

4. Having the 'doable' status and kap generation time and date visible on the status pages is already very useful. A quick indicator of the number of data items unentered for each chart record would also be handy. For instance, some of the non-doable charts have had just their non-doable status set, while others are missing only the few data items that make them non-doable. It would be useful to be able to distinguish between these. For anyone who is familiar with the interface, even just having the traffic lights replicated at the status screen level would be useful, when it comes to picking off the stragglers.

5. Lastly, in case you infer from the above that I'm dissatisfied with the interface, the opposite is true - I think it is superb!

Paul

[HappySeagull]

Recri,don't struggle.I agree with paulr
28201 is from a Mexican survey of 1905...so that's using a timepiece+sextant....and nobody's done much since.(Much of the landgrid of North America from the east coast to the western prairie was also "inaccurate" for the same reason....)
I'd just go from the info on it,without guessing HERE.No point recalibrating using iffy charts around it....?
My idea for these and other ones that seem to be OK but local knowledge knows are not is to, later,
have a place to put recalibrated +opinionated charts .

[HappySeagull]

...and by the way.Just because the best of these (the easiest!) old charts have been apparently recalibrated to WGS84 and they look fine to us from here...that doesn't mean they are Good Charts.the coastline could be drawn wrong,rivers shifted..all sorts of mistakes come into chartmaking.

[wdkester]

I'm having a problem with the chart validation tool. I'm using Chrome because it has more useable screen space. After calibrating about 10 charts, in the Ref Points section, the NE corner, I can't enter lattitude seconds or E/W, and of course, can't save the entry so far. Restarting the browser fixes the problem but loses the data entered.

[recri]

Originally Posted by HappySeagull

Recri,don't struggle.
28201 is from a Mexican survey of 1902...so that's using a timepiece+sextant....and nobody's done much since.(Much of the landgrid of North America from the east coast to the western prairie was also "inaccurate" for the same reason....)
I'd just go from the info on it,without guessing HERE.No point recalibrating using iffy charts around it....?
My idea for these and other ones that seem to be OK but local knowledge knows are not is to, later,
have a place to put recalibrated +opinionated charts .

Thanks Happy --

My project to reconcile Puerto Morelos and Yucatan Channel ended when I discovered that the two nav markers which appear on both charts are not the same distance apart. So how to resolve? Pick one? Split the difference? Rescale the chart? It was interesting to work through the puzzle and find no sound solution.

I see the NTM for this chart has 5 new lights, but no mention of any correction to the chart position. Plotting the lights on the chart, as the chart is labeled, puts them well offshore in deep water.

So what do you do when you find your chart plotter locating you on this chart? Will the plotter let you enter a locally determined correction? Or do you have to apply the correction in your head?

[recri]

Originally Posted by wdkester

I'm having a problem with the chart validation tool. I'm using Chrome because it has more useable screen space. After calibrating about 10 charts, in the Ref Points section, the NE corner, I can't enter lattitude seconds or E/W, and of course, can't save the entry so far. Restarting the browser fixes the problem but loses the data entered.

My only problems with Chrome (dev release on Ubuntu) have been that the server decides I'm not logged in and won't let me open a chart, or it decides I have a chart already open and need to close it before continuing. I need to logout, close windows, and discard cookies, sometimes more than once, before I can get back to chart editing. The trigger seems to be the amount of time that I've been logged in doing nothing.

[wdkester]

I'm looking at 26030 which has a datum note that reads (approximately) "Positions obtained by satellite nav systems (WGS72) must be moved by .06 min S and .01 min W"

Does mean we enter .08 SOUTHWARD .01 WESTWARD ?

his char has a corners problem so isn't of immediate concern. I just want to know if Irun across another like it.