Charts

[sinbad7]

Now, if we can find a nice Mercator worldview, we may be able to use it.

It is on my list to improve the current blue WorldVectorShoreline rendering. I agree that it takes too many cycles zoomed out.

Thanks
Dave

How about this clear and simple world map in Mercator projection?

Can be downloaded in 127 color tif here:

[manimaul]

Thanks guys,

OK, we can reproject as mercator:

gdalwarp -t_srs +proj=merc 189313rgb.TIFF bathy_merc.tiff
convert bathy_merc.tiff -colors 127 warp2.tiff
tif2bsb bathy_merc.kap.txt bathy_merc_127c.tiff BATHY.KAP

Use at your own risk:
BATHY.KAP
It appears to be spot on.

Will

[manimaul]

GPSMarco, Perhaps you could use gdal to fix some of your lambert projected charts.

gdalwarp -of GTiff -s_srs +proj=lcc t_srs +proj=merc <file.KAP> <new_file.TIFF>

edit KAP header and re-feed through libbsb

Will

[GPS-Marco]

Originally Posted by manimaul

GPSMarco, Perhaps you could use gdal to fix some of your lambert projected charts.

gdalwarp -of GTiff -s_srs +proj=lcc t_srs +proj=merc <file.KAP> <new_file.TIFF>

edit KAP header and re-feed through libbsb

Will

Wow! I'll try this way. Lambert projection is defined by at least the 2 meridians where the projection cone intersects the earth. There should be a way tso tell gdalwap those 2 meridians for a correct reprojection.

Ciao, Marco.

[sinbad7]

Marco..

Can I ask you to please check out a new World .kap conversion I made based on the last template you sent me. I just changed the geo locs but somehow it doesn't work. I had to enter the template separately.

The basic 127 color WorldMercator.tif file is in my dropbox. and the template used is as follows:

VER/2.00
BSB/NA=World-Mercator,NU=,RA=1503,810,DU=60
KNP/SC=150000000,GD=WGS84,PR=MERCATOR,PP=53.0,PI=0.0,S P=
SK=0.0000000,TA=00,UN=METERS,SD=MEAN LOW WATER SPRINGS
DX=5.0,DY=5.0
CED/SE=2002,RE=1,ED=2009
REF/1,445,743,-51.6907,-59.8242
REF/2,50,425,19.6150,-155.4785
REF/3,472,297,46.5991,-53.0859
REF/4,879,170,68.1076,45.3516
REF/5,1147,428,19.1521,109.6729
REF/6,1300,694,-42.3802,146.7188
PLY/1,-63.3786,-169.2740
PLY/2,79.0422,-165.2650
PLY/3,80.8003,-160.6431
PLY/4,-61.1108,-166.8467

Not sure why it does not work.

The scale is estimated to be 1:150 mill

[manimaul]

Opencpn crew,

Ok, I've been expirimenting with this overview/world chart. Dave, is this something that could actually replace those blue vector lines? I'm trying to make it look somewhat native to existing rasters. Does anyone have any thoughts. Labels, country borders, etc ... other handy features.

Thoughts?

[bdbcat]

Manimaul....

We could implement some KAP file as a default georeferenced background instead of the WVS blue lines.

I played with BATHY.KAP. We are working on some new algorithms for georeferencing of very small scale charts, and I guess this applies

For the new algorithm to work, we need the chart scale in
KNP/SC and the DU in BSB/DU to be pretty close to right and self-consistent.

I calculate the the scale of BATHY.KAP is about 1:127,900,000. Pretty small.

Here is how to calculate scale for a converted BSB chart:

1. Calculate a value for pixels-per-meter in the horizontal direction. You can get this from the REF values.

For BATHY, the chart extends 360 degrees in 3132 pixels horizontally.

Using WGS earth semi-major diameter of 6378137.0 meters, then

pix-per-meter = (3132 pixels horizontal) / ( 6378137.0 * 2 * PI)

For BATHY, I get about 7.8153 x 10e-5. pixels-per-meter

2. Then, chart scale is:

chart_scale = DU * 39.3701 / pix_per_meter;

For BATHY: scale = 254 * 39.3701 / (7.8153 x 10e-5) = 127,953,351

I think we can do a pretty good job of georef on these very small scale charts if we have accurate scale values in the KAP header.

Of course we could figure this all out in opencpn directly from the REF points. But I think we want the KAP to be as complete and accurate as possible....

Also note that the KAP header SC value is not used except as text info for charts with scale greater than 1: 5,000,000. So, those working on tif conversions for medium and large scale charts don't need to worry so much about the above calculation.

I'll think about how to use a world KAP as background paper.....

Dave

[sinbad7]

Marco..Dan... ref my #170

Having re-checked all my header data and the worldmercator.tif file again this morning and created another worldmercator.kap file,I find that the file created is only 185 kb whilst the worldmercator.tif file is over 1 MB,there is obviously something wrong.

Running tif2bsb it created the worldmercator.kap file WITHOUT the header which I added manually using a hex editor.

I am using the normal command line:
tif2bsb -c 127 worldheader.kap worldmercator.tif WorldMercator.kap

I have used the EXACT header template as advised by Marco with the addition of two extra REF points. The worldmercator.tif file is also correct with 127 colors.

[sinbad7]

Don't ask me how but here's MY preferred World Mercator projection I have put as my default chart in OpenCPN. With and without AIS targets.

Doesn't look quite right far up North by Norway. The cursor reading of the geo loc corresponds with the geo locs displayed in the query box.

[dacust]

I've been busy on other things, but here is what I got on the terraserver images.

The large rectangles are the small scale topo charts.
The little blocks of tiny rectangles are the large scale B&W photos I've shown before.

Click here for full size




And here is a topo chart in action:

Click here for full size




As you can see they don't EXACTLY line up. I think I know why and may have a fix.

Next I'll work on the large scale topos and the small scale photos. The only work is just figuring out the break points to break up the charts up into groups. It's basically a binary search to find the point where adding 1 makes it jump to another tile. Then doing it again one tile up to see how big a tile is.

-dan

[dacust]

Originally Posted by sinbad7

Don't ask me how but here's MY preferred World Mercator projection I have put as my default chart in OpenCPN. With and without AIS targets.

Doesn't look quite right far up North by Norway. The cursor reading of the geo loc corresponds with the geo locs displayed in the query box.

Hey, that looks great!

Wanna post it for anyone else who might like it? (Me for instance?)

-dan

[sinbad7]

Dan..

If anybody likes to have the WoldMercator.kap map you'll have to send me your e-mail address as this forum does not seem to allow .kap uploads, and re-naming the file corrupts it. The geo references are not exact but near enough for an overview.

[idpnd]

Originally Posted by manimaul

Does anyone have any thoughts. Labels, country borders, etc ... other handy features.

Thoughts?

This is a rather interesting question actually.

Perhaps the global chart should match the default S-57/C-Map colour scheme to some extent to get some continuity into the picture (as in Mani's example).

Torre's background image has got political country borders; perhaps this sort of thing could include the seaward national waters?

Low system load would also be a priority. It would be nice for it to be "pretty" since there is no navigational information at that display level.

[sinbad7]

Dan and all...

You can download my worldmercator-x.kap file here:

www.yachtmarine.com/httpdocs/worldmercator-x.kap

[idpnd]

The slashes in your link are the wrong way round Torre!