Imgkap - kap File Converter Tool

[HappySeagull]

denverdOn,
break it up if you like. You are making a rat-chart, but just check it out against a list of lights and other known positions to get a feel for the accuracy.
... The idea is to get a clear practical chart within it's scale of USE. All rasters (kaps) have some distortion so making a small scale chart bigger does not make you safer. The positions cannot all be as accurate as a large scale chart.


For a model, as to what we are saying, download some kaps from the US .See how they size them. It's a technique, that I don't say I've mastered, but I know it exists!

However, be that as it may, that you can't match my example, on your computer, is troubling. So, the next question will be, "What is your screen size in pixels?" My screen is 1024 x 768 across. (I would put on my creep hat, and deduce yours from a screen grab you posted, but I see you haven't one)

[cagney]

Originally Posted by denverd0n

I like the fact that it has a lot of detail, so I kind of hate to lose that. Do you think it would help to break it up into, say, four separate charts? But keep the current level of resolution in each?

.

The chart has not a lot of details, but is a good overview. It's not good enough to enter Gorda Sound for example (see pics below).
By going for a smaller size and lower resolution you will not loose any details. Check the NGA projects thread, this subject was discussed a lot.

Let's look at an example:


Entrance to Gorda Sound using your original. A zoom factor of 2.8.


The same thing with "my" smaller version.

As you ca see there is no loss in navigation details, but your version is slightly clearer. Note that both charts are a little over zoomed.
With your version you can zoom much more before noting pixilation, but that does not make the chart any more accurate. The accuracy of the chart is based on the original survey and has nothing to do with the size and resolution of the chart picture, as long as the picture is non pixilated at a zoomfactor of 2. Why just 2? Because normally any chart is based on a survey in twice the scale of the final chart. Read more about this subject in Nigel Calders excellent book "How to read a Nautical Chart", recently updated with a second edition.

My conclusion is still the same .

Thomas

[denverd0n]

Thanks again for all your help. I shrunk the original .png file down and recreated the .kap and now all seems to be okay. I guess OpenCPN just doesn't like files that are too big.

[HappySeagull]

naah. O likes big files ok. If your printed charts were four times the size they are now, you'd want smaller ones, I bet.

[Eric.]

Hi MdJ,

First off I really like what imgkap can do.

I have some global bathymetric data that I wanted to view on opencpn as a kap. However the code doesn't seem recognize the special case where lon0=lon1 to mean the globe rather than zero:

imgkap gda_world_70N_120E_70S_120E.png 70 120 -70 120

gedit imERROR - size of image is not correct
Extend widthin 6762 heightin 3723 to widthout 6762 heightout 0
ERROR - imgkap return 2

I was just curious is there a better way to specify this or does the code need some modification?

Thanks,
Eric

[nohal]

Eric...
I would probably cut the chart image in two (or even more to speed loading up) as a workaround. With quilting on, the resulting effect will be fine.

Pavel

[MdJ]

Hello Eric,

imgkap limit the latitude values ​​to +/-180°

Cut image seems to be the best solution.

Another solution is to generate kap file with -180/+180 and then change header with 120°

> Imgkap gda_world_70N_120E_70S_120E.png -70 -180 70 180
> Impgkap gda_world_70N_120E_70S_120E.kap header.txt

Change in header.txt -/+180 to 120 (PLY and REF)
> Imgkap gda_world_70N_120E_70S_120E.png header.txt

But same problem may arise for software display as OpenCPN

Alain

[HappySeagull]

I don't recall it being mentioned before in this thread so:

It's possible to extrapolate two diagonal corners from any two known positions. No calibration tool is needed. Just a useful image viewer to find x,y pixel positions of these Positions and some arithmetic to discover the positions of the diagonal corners of the chart image from these.
imgkap offers the correction values if you have it "wrong".
Resize image accordingly and run the command again.

[onehalfmoon]

Hi
I seem to hit a snag in convert GE images to KAP and I have not seem a similar post.

I am trying to build a series of GE images to cover a large bay. I have divided the bay into 4 images that share common edges. I convert "imgkap" each image separately and loading them in Open Cpn, the individual image load Ok and no problems. If I load any more than a single image (2, 3 or all 4) only one of the images is correct but the others are not.

Now this is the strange part. The incorrect loaded image(s) initially looks OK but as soon as I scroll the overall image, the GE image does not stay pin to the background image . As you can see from the attached screen shot.

Any suggestions??

Cheers Tom

[cagney]

Originally Posted by onehalfmoon

Hi
I seem to hit a snag in convert GE images to KAP and I have not seem a similar post.

I am trying to build a series of GE images to cover a large bay. I have divided the bay into 4 images that share common edges. I convert "imgkap" each image separately and loading them in Open Cpn, the individual image load Ok and no problems. If I load any more than a single image (2, 3 or all 4) only one of the images is correct but the others are not.

Now this is the strange part. The incorrect loaded image(s) initially looks OK but as soon as I scroll the overall image, the GE image does not stay pin to the background image . As you can see from the attached screen shot.

Any suggestions??

Cheers Tom

Check what opencpn.log has to say about your charts.

Thomas

[KyleYankan]

Hey HappySeagull,
I was hoping to use imgkap to generate a static image from kap files, based off my current location. As in a nautical version of the google chart on this page: Bad Wolf

However, while I can convert the .kap to a png as a whole, is there a way of doing it for only a specified location of the chart? Or do I have to read the headers myself, figure out the coordinates and distance/pixel, and use imagemagick to zoom in on the area?

[HappySeagull]

KyleYankan,
Using screen grabs....

Method 1 is simplest.
1)zoom to the level you want..
2)push the cursor into the corners of the chart and write down the two diagonal corner positions (O shows cursor position on the bottom)
3) screengrab and carefully crop the screengrab ...
4)offer it all to imgkap..

IF you get the positions-versus-pixels wrong, imgkap will tell you- in that case, if you are not far off,try a resize of the image as imgkap directs.I found I got pretty good at cropping pretty fast, so it mostly worked with no hiccups.

Tip: get O to use decimal degrees in the User Interface Tab...easier for this stuff,I find.

Method 2
1) you can just create a box route with O's route-manager being careful as to directions ie:90,then180,then270 then 360...(and O will ask, "Use the waypoint?" voila the box is closed.Now,IF you like, double-check the marks you made so that the box really is rectangular in the mercator way by editing the corner positions ...(in a clockwise-made box,upper left latitude =upper right latitude ,upper right long =lower right longitude,etc.) Do this so the crop works nicely even though you only need the two diagonal corners for imgkap
2) then make a screen-grab
3)carefully crop the screen-grab to the route- box and save it(...I try to bisect the route arrows)
4)use the (ahem) "route"'s positions of the corners you can read out of O's Route-Manager or, if you like, from an exported gpx...easier to copy and paste from these..
4)offer it all to imgkap..

there's sort of an example here: if you can get by the obsolete clucking http://www.cruisersforum.com/forums/...tml#post657151


There's a third way- finding lat/long of corner pixels by extrapolating from known positions on a screen grab OR a cropped chart image. I can't see any quality difference between screengrab and chart image but ...I'll explain it if you think you need it.

By the way, I think phiggins' GE2KAP can do this!

[HappySeagull]

...I'd say I prefer the route-crop method...just square up the box in the Waypoint Properties dialogues at each corner by copy+paste to the NEXT wpt...ie: copy upper left corner lat to upper right then copy upper right Long to lower right then copy lower right lat to lower left etc etc....You can also be pasting these into a .cmd or .bat file as you go, to save time.
Another tip...Use combination CTRL and + or - keys to finely control the area for the screen grab.
Took me total much less than 5 minutes. It is really easy. (I'm using irfanview)

[germainm]

i'm trying to extract the png from a .kap generated by imgkap but everytimes it says ERROR - Invalid index table in (null)
ERROR - imgkap return 3

could somebody help me? i put the kap file here : http://www.searchevolution.com/109.kap

[cagney]

Originally Posted by germainm

i'm trying to extract the png from a .kap generated by imgkap but everytimes it says ERROR - Invalid index table in (null)
ERROR - imgkap return 3

could somebody help me? i put the kap file here : http://www.searchevolution.com/109.kap

The problem is that you, probably, have edited the kap file without running "bsbfix" (part of libbsb) afterwards.
To fix this just run: $bsbfix 109.kap
Then you'll get the picture with:$imgkap 109.kap 109.png

Thomas