Charts II: NGA - 2700 Charts

[AussieGeoff]

Ah, I see. It appears that most of the south coast is conspicuous by its absence. Looks like the east coast, down around the south to Melbourne, north coast and west coast are covered and so is Tassie. If you are going from the west coast to the east coast south of the continent, you are SOL.

Darn things must exist somewhere. Time to do some digging I guess.

Thanks...

Aussie Geoff

[recri]

I've looked at the following charts:

24123 - misprinted corner coordinate
23023 - error in corner coordinate entry
23145 - error in corner coordinate entry
71402 - error in corner coordinate entry
71400 - looks okay
71350 - looks okay
71330 - looks okay
71455 - minor adjustment to REF points
22531 - looks okay, no corner coordinates
22533 - looks okay
24121 - looks okay
24215 - looks okay
29325 - looks okay
63361 - looks okay
91407 - looks okay

[recri]

NGA 2700 chart summary for Sat Sep 24 17:11:25 GMT 2011
processed: 1419 charts
evaluated: 1279 charts
pxhoriz: mean 1.00000 stddev 0.00015
>5*sd: 24311 93032 55001
>4*sd: 36005 21182 53091 56190
>3*sd: 42740 44187 54085 400 51150 107 51022 108 20 29123 621
pxverti: mean 0.99999 stddev 0.00014
>4*sd: 53290 56190 53287 24319 53266 43340
>3*sd: 18766 14003 26001 21182 61190 92200 44342 55001 22036 57220
pxsquare: mean 0.99999 stddev 0.00017
>3*sd: 63354 24381 93032 703 52160 53203
ratio: mean 1.00492 stddev 0.00178
censored: skipped 115 charts: 11 62 70 105 106 121 124 125 126 145 301 520 521 522 524 526 532 622 623 701 707 800 21141 21161 21621 21641 22100 22314 22404 22440 22528 22531 22533 22541 22542 22549 23051 23121 24121 24152 24154 24159 24215 24444 24511 26125 29282 29322 29324 29325 42036 42046 54289 54303 57022 61003 63015 63361 71009 71012 71018 71036 71140 71330 71350 71400 71455 73034 74024 76201 81016 81127 81145 81303 81329 81427 81511 81563 81565 81576 81616 81729 81737 81791 81796 82025 82304 82384 82534 82564 83010 83020 83039 83052 83105 83218 83392 83495 83555 91020 91030 91060 91096 91314 91326 91407 92025 92030 92033 92040 92050 92140 92190 92560 96036
notmercator: skipped 25 charts: 14221 17421 18419 28164 29323 43064 43263 43344 43363 43371 43377 43378 43386 44192 44310 54362 54364 54368 55064 56191 76171 76181 81327 82071 91286
-----
Processed all charts with status:
+ 'Rectangular, doable'
+ 'Rectangular, partly doable - rectangular insets'
+ 'Rectangular, partly doable - non-rectangular insets'
+ 'Rectangular, not doable in Phase 1 because of special PLY's needed'
+ 'Chart done, checked and locked'
'processed' is the number of charts processed
'evaluated' is the number of processed charts that didn't get skipped
'pxhoriz' compares the lengths of the N and S edges, which should be equal
'pxverti' compares the lengths of the E and W edges, which should be equal
'pxsquare' compares the lengths of the NE-SW and NW-SE diagonals, which should be equal
'ratio' compares the aspect ratios of the REF point rectangle and the projected corner
+ coordinates, which should be equal
All those 'shoulds' are assuming a rectangular chart area in mercator projection.
'>n*sd' charts are greater than n standard deviations from the mean
'>5*sd' should be none
'>4*sd' should be none
'>3*sd' should be 3/1000 of the charts processed
All those 'shoulds' are assuming a normal distribution.
'censored' are outliers previously checked and looked 'okay',
+ there may still be a problem with data entry, or the chart may just be crooked.
'notmercator' are charts that aren't mercator or unknown

[HappySeagull]

..By the way,I noticed that Ze'ev and I are both doing the same thing with the charts that have bits sticking out beyond the borders....we are calibrating them completely so they can be downloaded as kaps but we are calling them "un-doable because Special Plys needed".
I think now this is the correct approach (because they can be easier "re-plyed" when the insets are?)but what does everyone else think?

PS:I wasn't doing this until halfway down in the 6000's so maybe I better go back...?oh looks like somebody did em-thanks!weren't many.

[recri]

Originally Posted by HappySeagull

..By the way,I noticed that Ze'ev and I are both doing the same thing with the charts that have bits sticking out beyond the borders....we are calibrating them completely so they can be downloaded as kaps but we are calling them "un-doable because Special Plys needed".
I think now this is the correct approach (because they can be easier "re-plyed" when the insets are?)but what does everyone else think?

PS:I wasn't doing this until halfway down in the 6000's so maybe I better go back...?

That's what I've been doing. I figure if you open the chart you may as well put in everything you can. And since the KAP can usually generated, you can check what you put in. I usually comment where the extra PLY's are required, by edge and corner.

[siff]

Originally Posted by HappySeagull

..By the way,I noticed that Ze'ev and I are both doing the same thing with the charts that have bits sticking out beyond the borders....we are calibrating them completely so they can be downloaded as kaps but we are calling them "un-doable because Special Plys needed".
I think now this is the correct approach (because they can be easier "re-plyed" when the insets are?)but what does everyone else think?

PS:I wasn't doing this until halfway down in the 6000's so maybe I better go back...?oh looks like somebody did em-thanks!weren't many.

I did the same in the serie 2, but i qoted them as rectangular doable to be able to use them. should i change the header ? I did not know that the kap could be generated when they were quoted as undoable ...

[recri]

Originally Posted by siff

I did the same in the serie 2, but i qoted them as rectangular doable to be able to use them. should i change the header ? I did not know that the kap could be generated when they were quoted as undoable ...

I corrected the west american charts that I did that way when I figured out the KAP's were generated in spite of being "Undoable". We eventually will need to know which charts need extra attention to be finished.

I just went through the comments to the region 2 charts and fixed 2 that were commented as needing PLY's but identified as "rectangular doable". They were 21121 (one of mine), and 28162.

[HappySeagull]

Originally Posted by siff

etc..I did not know that the kap could be generated when they were quoted as undoable ...

Siff,don't run back and hunt em down yet
they are hard to spot from the thumbnails so it takes too long and there won't be many.They'll pop up later anyways,if it really matters.And I don't know that it does
...I discovered it by accident.
That said,The ones with "thumbs" are as possible as the "doable with insets".It's really the same as a chart with insets except the insets are outside the chart.I'm betting both these will rely on the first calibration to finish,so,the only thing I'd change is undoable to doable.They still need some way to note them and return easily,when the tool exists to fix em.

[z.stadler]

72050 has a strange combination of two notes:

Datum Note:
Adjustments for plotting positions obtained from satellite navigation systems based on the World Geodetic System (WGS) cannot be determined for this chart

Note:
Later determinations indicate that all meridians on this chart should be shifted by approximately 18" westward; in effect decreasing coordinate values by 18" of longitude

There are several questions here:

1. Should the second note be considered as superseding the datum note?
   I assumes we should consider it
2. What's the datum for of the correction specified in the second note?
   I assumed WGS-84
3. If the meridians on the map should be moved westward, what does that mean for the shift of WGS-84 coordinates?
   I assumed they should be moved 0.3' eastward, 0.0' northward

Comments?

[HappySeagull]

Ze'ev,I'd use the latter and note that you did in the comments box.
and I'd do it as in
"0.3" (minutes) then "Westward" just as it says..
And then I'd download it and see if it is right with other better charts in the area for what that may be worth.(don't use cm93 charts unless they ARE KNOWN to be spot on...)

http://www.cruisersforum.com/forums/...tml#post768652

in a previous post,Cagney (Thomas) describes what process is used to make the kaps from these.Basically it does what you would do calibrating the image yourself-reversing our input -in a way,our entry describes what you'd do to the chart- notthe positioning .

And entering as it says is way easier on us.

[HappySeagull]

18" is a big correction!wow.That one could be checked with googlemaps,I bet.
here's Thomas's explain
http://www.cruisersforum.com/forums/...tml#post767215

[P_Dub]

What is the address for the finish product (.kap) file format? Or do we have to do it ourself for each one?
Regards
P_Dub

[paulr]

Originally Posted by z.stadler

72050 has a strange combination of two notes:

Datum Note:
Adjustments for plotting positions obtained from satellite navigation systems based on the World Geodetic System (WGS) cannot be determined for this chart

Note:
Later determinations indicate that all meridians on this chart should be shifted by approximately 18" westward; in effect decreasing coordinate values by 18" of longitude

There are several questions here:

1. Should the second note be considered as superseding the datum note?
   I assumes we should consider it
2. What's the datum for of the correction specified in the second note?
   I assumed WGS-84
3. If the meridians on the map should be moved westward, what does that mean for the shift of WGS-84 coordinates?
   I assumed they should be moved 0.3' eastward, 0.0' northward

Comments?

I think you've got it the wrong way round, i.e. I suspect that the "note" preceded the "datum note".

It's not that someone decided it couldn't be made WGS compatible and then realised it could, by adjusting the meridians.

Rather, it was realised at some time between 1907 and probably 1959 that the 18" correction was necessary to correct the chart to the originally intended datum (which could have been more or less anything).

The datum note would then have been added later, as on many other charts, to warn that you can't use this chart with a GPS.

So your assumption about WGS84 is unjustified, in my view. I've changed it to "unknown", which is what that option exists for. So, it's an unknown datum, corrected to an unknown datum, which is all that you can deduce from the chart.

Paul

[z.stadler]

Originally Posted by HappySeagull

18" is a big correction!wow.That one could be checked with googlemaps,I bet.
here's Thomas's explain
http://www.cruisersforum.com/forums/...tml#post767215

The "usual" datum note text, as given in Tomas's explanation, refers to the translation of WGS-84 coordinates to map coordinates.

The text of the note in this example, refers to the correction in the map coordinates ("all meridians on this chart") to some unknown datum. That's why I think it needs to make a reverse correction from WGS-84 to the map.

An any case, I'll take your advice and see if the correction is worthy.

[cagney]

Originally Posted by paulr

I think you've got it the wrong way round, i.e. I suspect that the "note" preceded the "datum note".

It's not that someone decided it couldn't be made WGS compatible and then realised it could, by adjusting the meridians.

Rather, it was realised at some time between 1907 and probably 1959 that the 18" correction was necessary to correct the chart to the originally intended datum (which could have been more or less anything).

The datum note would then have been added later, as on many other charts, to warn that you can't use this chart with a GPS.

So your assumption about WGS84 is unjustified, in my view. I've changed it to "unknown", which is what that option exists for. So, it's an unknown datum, corrected to an unknown datum, which is all that you can deduce from the chart.

Paul

I agree with your deductions. The 18" note is typical for corrections on pre WGS charts. No note today, would be made without reference to WGS (hopefully!).

My interpretation of NGA:s WGS datum note, is that it has been found impossible to bring this chart to agree with WGS84, with a single correction.
With reference to WGS 84 the chart is warped in some way.

Thomas

PS. To see some very old, similar notes, check 83225.