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Old 30-07-2017, 13:21   #1
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Feature Request: Set KAP file transparency

For weatherfax image files, Exported as KAP, I have set up a Chart-Wxfax directory, which I've added to the Charts paths and scanned db. Then I've added a Group for wxfax kap.

Now when I load those wxfax Kap (with a right click and select the wxfaxKAP group) I get about 10 - 15 chart buttons at the bottom.

I would like to be able to right click on a chart button and adjust the transparency of that KAP.

For the time being is there a way to adjust transparency by putting something in the header?
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Old 30-07-2017, 18:40   #2
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Re: Feature Request: Set KAP file transparency

[QUOTE=rgleason;2445013
I would like to be able to right click on a chart button and adjust the transparency of that KAP.
[/QUOTE]

I like this suggestion. I have previously used the GE2KAP program to make semi-transparent KAP charts where cm93 has depth information (fairly rare in my part of the world) that would show through the GE overlay image. What you propose would be a better solution.

Thanks, Terry
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Old 31-07-2017, 05:44   #3
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Re: Feature Request: Set KAP file transparency

kap files do not support transparency. kap files do a horrible job at compressing satellite imagery.

mbtiles can solve both of these problems and more, but it's not natively supported yet...
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Old 31-07-2017, 12:37   #4
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Re: Feature Request: Set KAP file transparency

I believe you Sean about mbtiles and it would be great if Opencpn supported it. How much time and resources would be required to accomplish that?

- I guess there's no point in asking because you may have decided that that is the best way to solve a number of things.
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Old 31-07-2017, 13:33   #5
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Re: Feature Request: Set KAP file transparency

Sean, what if we could get kap satellite files really easily.
Is there a way to turn them into MBTILES easily?

What if we were to have Weatherfax files that are exported as KAP, would there be a way to turn them into MBTILES easily?
Would we be able to control transparency so the underlying charts can be seen?

Thanks.
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Old 31-07-2017, 15:44   #6
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Re: Feature Request: Set KAP file transparency

As many have found, sasplanet or mapproxy already creates mbtiles from many sources including satellite image.


I wrote python scripts to convert to and from kap to mbtiles (http://github.com/seandepagnier/mbtiles-nautical-tools) It makes more sense to convert mbtiles to kap. This is why I don't have much priority to support mbtiles in opencpn, because you can just convert them to kap.

When you do, you lose transparency, and also the compression is much worse, and random access (mbtiles are tiles very efficient) is lost as well, as kap you must read the whole scanline.

If you convert kap to mbtiles you almost always lose data, or end up with a larger file, because mbtiles only supports specific zoom levels.
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Old 31-07-2017, 17:14   #7
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Re: Feature Request: Set KAP file transparency

So that leads me to the request to make Kap files transparent. I have to digest this a bit.

On another matter, can you use a python file that will download UK Met weatherfaxes with weatherfax_pi so we can get the UK Met files?
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