KAP Files Help appreciated

[HappySeagull]

I read bcn's pdf and apparently maptech likes to have GD=eclectic too (section 5.2 "Image file parameters" but that is dumb.If it bugs you that wgs84 grid doesn't match the drawn lines of lat and long, the drawing's refs are on the picture itself.

,.

OR the nav program should ignore GD as a reference to plotting.

[moseriw]

Originally Posted by HappySeagull

Attachment 118053

Wow, thank you seems to fit but I have to dive deeper in it as I want to make 30 of them + a lot of harbour charts.

Will report my efforts here for followers.

Many questions... chart size is 1:10000 yours is different - will find it out
sizeing... is there a percentage to add?
DU=254, scan is 300
IS DX,DY essential?

btw:
Bessel 1841 is agreed by scientists as the best chart datum ever - don't ask me why I foregot it. Bessel was an Austrian and the politics...

Nowadays it is simply stupid (maybe expensive) to convert to WGS 84 so the official charts are Bessel 1841

Thank you very much for your help... I go digging

[moseriw]

btw. the reason why the chart was not north up was OpenCPN. I had to reboot for another reason and then all OCPN settings were gone. So I uninstalled and installed 4.0 again and the chart was north up and in position.
Well not exactly but nearly. Think I have to cheat with the REF points.

Funny things happen.

[HappySeagull]

Originally Posted by moseriw

Wow, thank you seems to fit but I have to dive deeper in it as I want to make 30 of them + a lot of harbour charts.

Will report my efforts here for followers.

Many questions... chart size is 1:10000 yours is different - will find it out
sizeing... is there a percentage to add?
DU=254, scan is 300
IS DX,DY essential?

btw:
Bessel 1841 is agreed by scientists as the best chart datum ever - don't ask me why I foregot it. Bessel was an Austrian and the politics...

Nowadays it is simply stupid (maybe expensive) to convert to WGS 84 so the official charts are Bessel 1841

Thank you very much for your help... I go digging

Well, the bessel 1841 probably isn't hurting anything because opencpn isn't using it and the chart is apparently calibrated to wgs 84 anyways...But it's a peeve of mine is all and could be trouble for someone else (as in "Seaclear" program)

I ended up editing all my so-called NAD27 charts to wgs84. I got sick of O whimpering about it in the logfile. It didn't take long with Notetab as a batch operation using "find and replace" and a macro but with your longer "Bessel 1841" you will need experiment with bsbfix or add carefully some spaces to keep it right per hex. You can't remove characters without some practise.
and of course, now you are messing with "originals" and you should say so some where in it or never pass your charts off to someone else, because they won't care.

imgkap set the scale,DU and whatever else. I just offered a blank ".png" image of your original size (per your header) and gave imgkap the two diagonal corners from your header.
sometimes though, imgkap will balk and throw an error about image size without proceeding. If that happens, I resize the image as imgkap suggests in the error. yes, there is also a formula that can be used ..I recall degrees longitude should be spaced per cosin of the images mid latitude. so rougly speaking it is to say a chart showing 1 degree of latitude and 1 degree of longitude at 30 degree latitude will be proportioned half as wide as it is long....usually, charts don't look so thin but you can see where I'm going with this, I hope.... it's a way to resize any image correctly if you know how many pixels height there are per degrees latitude included in the image and how many pixels width per longitude included
But it's easier believing imgkap! whichever, I resize the image with irfanview or xnview and save as png.
Tip: xnview has a plugin to view "kap" files. Very handy.
another Tip: png files are not lossy and limited to 256 colours- an easy good idea. Kaps have limited palettes, so a reduced palette speeds things along, versus churning through 16 million colour jpegs! where only 16 colours can be fine.

add: don't forget that making a kap file from an image is a compression operation...change to a new image format.Are you are making kaps from scanned charts? if so, Whatever you are using to "render" these from the scanned images is "doing things".

Scale is too much for me to make up an explanation about here though I have copious notes-to-self"stached somewhere!) but simply, have a look at real charts and compare to image size using xnview.

add: or use this. Just drag the kap onto it. (rename as .cmd, put it in the folder with imgkap and the kap file) Works for me- hopefully others too.

DRAGKAPontothis-andExtract.txt

if not, the command is

imgkap.exe "whatever.kap" EX.txt EX.png

to get two files; picture and header text named EX.txt and EX.png. you can change those if you want.

The quote marks are useful if your kap name has spaces in it. but better to avoid spaces.

[DavidBurch]

There is much online here on related topics, but since it still took me a while to make this work for weather maps, I have posted a note with detailed steps and video illustrations on converting weather maps to BSB format to read in OpenCPN. The next step is to make another post showing why this is valuable. See Converting Images to BSB echarts with MapCal_2, mc2bsbh, and imgkap

[DavidBurch]

it marks the beginning of a comment line.

[HappySeagull]

oh gee. I mean 60 deg lat.(cos60=.5)

it is to say a chart showing 1 degree of latitude and 1 degree of longitude at 30 degree latitude will be proportioned half as wide as it is long

[HappySeagull]

Originally Posted by DavidBurch

it marks the beginning of a comment line.

Do you mean the exclamation mark in the " ! - DTM/0.60,16.80"
that bcn spotted? that seems a good possibility .

There is much online here on related topics, but since it still took me a while to make this work for weather maps, I have posted a note with detailed steps and video illustrations on converting weather maps to BSB format to read in OpenCPN. The next step is to make another post showing why this is valuable. See Converting Images to BSB echarts with MapCal_2, mc2bsbh, and imgkap

I can't see anything here at the link...but it reminds me to mention the opencpn weatherfax plugin that can convert weathermaps (and other maps too) to kaps. Worked pretty well for me on a few clumsy tests but I haven't "certified" myself to operating it.

[DavidBurch]

Originally Posted by HappySeagull

Do you mean the exclamation mark in the " ! - DTM/0.60,16.80"
that bcn spotted? that seems a good possibility .





I can't see anything here at the link...but it reminds me to mention the opencpn weatherfax plugin that can convert weathermaps (and other maps too) to kaps. Worked pretty well for me on a few clumsy tests but I haven't "certified" myself to operating it.

First, yes !, but DTM is a real parameter

DTM

Datum Shift Record

3.4.2.12

Horizontal datum shift to WGS84
i have just been using DTM/0.0,0.0

Second, not sure why the link does not work. This is it written out: David Burch Navigation Blog: Converting Images to BSB echarts with MapCal_2, mc2bsbh, and imgkap

References: the bottom of this note on the header file lists the best links to BSB format i have found David Burch Navigation Blog: Weather Maps to eCharts—Making the Header File

[moseriw]

Report of findings:

The DTM is important! you can home in to an exact position comparing the new chart with an existent, in my case CM93.

MapCal_2.exe >> mc2bsbh.exe >> imgkap.exe gave me errors so I skipped it.

By now I will experiment with the pixels as the chart itself is not converted correctly. S is ok with DTM but N is N -0,38 E +100m off.

I am sure the problem is with the pixelsizes.

Will post a conclusen when it fits perfect.

[HappySeagull]

Originally Posted by moseriw

Report of findings:

The DTM is important! you can home in to an exact position comparing the new chart with an existent, in my case CM93.

MapCal_2.exe >> mc2bsbh.exe >> imgkap.exe gave me errors so I skipped it.

By now I will experiment with the pixels as the chart itself is not converted correctly. S is ok with DTM but N is N -0,38 E +100m off.

I am sure the problem is with the pixelsizes.

Will post a conclusen when it fits perfect.

You would know best , however as a point of opinion that might save intense trouble fitting an image to suit cm93....
I would not trust cm93 so far as that. They are ok, but are themselves based on various raster charts and you don't know which exactly.... Personally, I would prefer up-to-date, official "Lightlists" over cm93- these have the positions per wgs84 .They are usually free, I think..?

I would say, DTM is easy when calibrating points use the map image's lat and long scale. And sometimes it works fine, depending on whatever map image you are using there....(I've tried to calibrate some pretty iffy scanned maps on occasion- the grid never got straight)) But if you use wgs84 positions (favouring the centre of the chart if possible) or adjust the calibration points to be wgs 84 compliant, DTM can be made as 0,0. ... it's still not really a wgs84 Chart (per the old survey of shorelines and rocks) but at least the lighthouses and navigation marks are as wgs84 compliant as you can get without visiting them with a gps in hand.

I would at least also test your charts against known wgs 84 positions and not just cm93.

[moseriw]

Thank you for the input and the infos about CM93. I really thought they are accurate I have the list of lights - of course.

Just to mention
NW REF1
NE REF2
SE REF3
SW REF4

the howto at OpenCPN is incorrect. DTM is not a good solution as it moves rhe chart out of the border frame. So I will set the border to the chart's positions and experiment with the REF's to find the exact matches with real coordinates.

btw. If you set the border and REF's to the same coordinates and the chart does not match the frame... I measured the chart and difference in NM's built a percentage and resized the chart's pixels.

[rgleason]

MoserIw

the howto at OpenCPN is incorrect. DTM is not a good solution as it moves rhe chart out of the border frame. So I will set the border to the chart's positions and experiment with the REF's to find the exact matches with real coordinates.

Would you mind helping others since you think the "How to" is incorrect?
First - Where is this How to?
Second - How would you change it?
Third - If you have registered on the opencpn.org website here
you can edit the user manual yourself.

The user manual is here OpenCPN User Manual | Official OpenCPN Homepage
I assume you are talking about some part of the user manual being incorrect.

For instructions about how to edit the user manual please refer to this page.
Edit the User Manual | Official OpenCPN Homepage

Thank you.

[moseriw]

how to edit the user manual.

Thank you for the hints. Once I am through with the damned charts I will update the imgkap and the kap file | Official OpenCPN Homepage page but it will take some time.

[rgleason]

Moseriw, thankyou so much. That will help everyone.