Charts

[cagney]

Originally Posted by HamishB

.........
..........
I had a look at the problematic NZ14065 chart (NZ to Antarctica) talked about earlier in this thread. It's standard Merc with a latitude of true-scale at the equator, so no special transform is needed or should be done. By knowing the projection is merc, the datum is wgs84, the dpi (from tiffinfo), and the scale & +lat_ts from what is printed on the map, we have everything we need to georectify the map perfectly. Using poly fits for raster maps which are not distorted will only degrade and confuse matters. If the map is thought to be correct and things don't line up, then it's time to blame the software I haven't actually tried to georeference it yet, so this is just chatter.


regards,
Hamish

You are spot on with 14065. This is exactly how OpenCPN now treats 14065 and similar small scale charts, and with very good result.
A look at the log file when loading Marco's NZ charts

10:15:16 AM: Initializing Chart /opt/Navigation/Raster2Bsb/World/SPAC/NZ14065.kap
10:15:16 AM: Small scale chart georef Mercator override activated...
10:15:16 AM: Using minimal 2 REFpoint solution

So even though Marco has 20 REF/s OpenCPN is only using 2. Are the other ones for SeaClear and other plotters ???
I think that the easiest way to geo ref these charts is to use the 4 corners as REF/:s and then copy the lat&long for the PLY/:s, this also gives OpenCPN the best 2 point solution.

I helped Dave with some testing, and we had big problems with 14061 as long as polys were used. It seemed like no matter what I did there were problems, one way or the other.
A 'pure' Mercator solution, including compensation for eccentricity, solved this problem.

Thomas

[idpnd]

Velero Olaje Cartas Nauticas para descargar

Some med charts here - if these have been posted before, sorry to bore you

[sinbad7]

idpnd..

GREAT map source,thanks a million.....will keep me calibrating for weeks...

[Totobeloeil]

Great source !
I can help but I don't know what is exactly to be done.
Many of these charts are already georeferenced by a '.map' file (OziExplorer / WGS84).
Do we only have to put them in 'BSB / Google' format ? What about margins ?
The other ones need to be calibrated. I did not read the whole thread about it. What should be done ? Is there a program where we can slide the map upon an 'already georeferenced' one ?
Jean-Pascal

[sinbad7]

Totobeloeil..

The charts with the .map suffix can be used directly by the OziExplorer nav. prog.

And,the .map calibration file can be used also to convert the .tif map to the SeaClear nav. prog. format using MapCal.(comes with SeaClear)

MapCal procuces a calibration file CHARTCAL.DIR which can be used to convert the
.tif map to a .kap chart readable by OpenCPN and other nav. progs.

You first have to convert the .tif file to .png and change it to 127 colours.
Easily done in the free GIMP2, and then use another free program called 'ChartConverter' for the final,automatic conversion process to a .kap (bsb) chart.

Download ChartConvert here in .z7 compressed format:

You can also convert all the other .tif or .jpg or .png charts to .kap by entering the maps corner co-ordinates in MapCal.

The process is thoroughly explained in one of the threds in this forum.



Good luck....

[Totobeloeil]

Thanks, Sinbad.
I would like to find something simpler or more automatic, based upon projection rather than calibration.
I have only a very little idea of what projection OpenCPN needs really because there are several official codes refering to what is usually called 'MERC' or 'TMERC'.
Never mind, I'll try and let you know ...
Jean-Pascal

[brak]

Originally Posted by HamishB

I've been using libgdal as part of desktop apps every day for years without any complaint. shrug. The dependency tree can be huge if you build it with all the bells and whistles, but you don't have to do that.

You certainly can use it, but for S57 charts it is extremely "low performance". I am not sure how well it works with raster chart data, never tried that, to be honest.

To the point though- quilting is only ever going to be useful for maps which share a common native map projection, for the rest you'll have to be happy with a reprojected PLY-style bounding polygon (perhaps filled 75% alpha transparent) showing where the map is. As 90% of the nautical charts out there are Mercator, this isn't a huge tragedy, although it does mean switching out of quilt mode when you enter some harbours (where trans.merc can be found) or when you zoom to the continental scale (where polyconic projections can be used).

It should not be a huge problem for harbor charts too, since at small harbor scale projection matters very little - chart will likely fit within a pixel or two whether it is Mercator, Transverse Mercator or even simply direct scale of distances.

I had a look at the problematic NZ14065 chart (NZ to Antarctica) talked about earlier in this thread.

After it's been mentioned so many times I am now extremely qurious about that chart and how special it is If anyone here has it in BSB format for me try - I'd be very grateful for the info.

[Totobeloeil]

Hi Sinbad,
I tried to calibrate some of the last mediterranean charts. Here is the CHARTCAL.DIR file. As it's my first trial, it would be great if you take time to have a look .
I made some .KAP files too. Now trying to automatize a bit with tools used by Marco for kiwi charts.
Jean-Pascal

[idpnd]

Note that the copyright for the med charts isn't clear, so we probably can't redistribute them legally.. We could send the calibration file to the chap I guess

Los archivos que puedes descargarte de esta web provienen de diversas fuentes, fundamentalmente encontradas en Internet, y las considero de libre disposición, por lo que no existe interés comercial de ningún tipo.

[Totobeloeil]

That's a good idea. I didn't care much about that question but it's important.

[Totobeloeil]

Sinbad,
I made small cmd files to proceed after MAPCAL. It's based upon the tools Marco made. Not so beautiful, but could be useful ... I did not include programs (bin directory) as there are the same.
Jean-Pascal

[SailNomad]

Hello,
I am trying to decode the information in the KAP file, but have some problems. I am trying to find out what the region is, that the cahrt covers:
Here is an example:
(from US char 13272_1.KAP BOSTON INNER HARBOR)
(I know there is info in the BSB file, but the projection parameters are in the KAP file)

------------------------------------------------------
CRR/
VER/3.0
BSB/NA=BOSTON INNER HARBOR,NU=2082,RA=11393,9390,DU=254
KNP/SC=10000,GD=NAD83,PR=MERCATOR,PP=42.367,PI=1.000
SP=Massachusetts Mainland,5000,SK=0.0000000,TA=90.0000000,UN=FEET
SD=MEAN LOWER LOW WATER,DX=1.00,DY=1.00
KNQ/EC=RF,GD=NARC,VC=UNKNOWN,SC=MLLW,PC=MC,P1=UNKNOWN, P2=42.367
P3=NOT_APPLICABLE,P4=NOT_APPLICABLE,GC=MJ,RM=POLYN OMIAL
CED/SE=49,RE=01,ED=10/01/2004
NTM/NE=49.159,ND=04/26/2008,BF=OFF,BD=10/01/2004
etc etc
-----------------------------------------------------------------
The above says that the Projection is PR=Mercator, and the scale is SC=10000. the PP is 42.367 which is the correct Latitude
However, I can not find what the Longitude is. It should be somewhere in the vicinity 0f -71.03.
What Am I missing here ?
Thank you

[sinbad7]

SailNomad..

The PP=latitude is probably the latitude of SC=scale as an average.

You will find the actual geo co-ordinates of the chart further down in the
REF and PLY data.

See example from Bodoe,Norway below:

! Created by mc2bsbh-0.00.01 - Use at your own risk!
BSB/NA=Bodø harbour - USE AT YOUR OWN RISK!
NU=,RA=1279,768,DU=0
KNP/SC=14993,GD=WGS84,PR=MERCATOR
PP=0,PI=UNKNOWN,SP=UNKNOWN,SK=0.0
UN=UNKNOWN,SD=LAT,DX=5.09,DY=5.09
REF/1,926,144,67.296450000000,14.373016666667
REF/2,861,478,67.280650000000,14.365883333333
REF/3,530,435,67.282283333333,14.325200000000
PLY/1,67.301902024175,14.2597678450332
PLY/2,67.266212286525,14.261662248748
PLY/3,67.2677141466267,14.4172235038098
PLY/4,67.3034016512546,14.415329100095
DTM=0,0

[SailNomad]

Thanks that helped. Using a simple google static map with markers (Thank you emacs cut and paste) I can see that the PLY's (12 of them) seem to be all corners of all the insets, so the max and mins should give me the chart area.
Don't know yet what the Refs are. There are 69 of those
Thanks again

[dacust]

Originally Posted by SailNomad

Thanks that helped. Using a simple google static map with markers (Thank you emacs cut and paste) I can see that the PLY's (12 of them) seem to be all corners of all the insets, so the max and mins should give me the chart area.
Don't know yet what the Refs are. There are 69 of those
Thanks again

The REFs are the reference points. Known points that connect the pixel location to a geographic location.

The PLYs form an outline of the usable area of the chart (specified with geographic numbers). This outline is what shows in OpenCPN as the red outline, and is used to determine when to switch to a new chart.

In the example in the post by Sinbad,

REF/1,926,144,67.296450000000,14.373016666667

This is the first REF point. It is at pixel location 926x478. And geographically, that point should be displayed at 67.29645 x 14.37...

PLY/1,67.301902024175,14.2597678450332
PLY/2,67.266212286525,14.261662248748
PLY/3,67.2677141466267,14.4172235038098
PLY/4,67.3034016512546,14.415329100095

These PLYs form a box with 4 sides.

-dan