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?
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.
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.