[Qgis-user] S57 map files

[Chris h]

On Sunday 18 January 2009 11:04:13 Florian El Ahdab wrote:

> So here are my questions:
> - has anyone ever worked with S57 and OGR and/or Qgis?

This discussion came up on the gpsdrive list and i've included the pertinent 
parts for you review: 

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From Hamish Bowman:

For ENC support in GpsDrive it is still my hope that libS52
could be used to render the data, in a similar way as Mapnik
is rendering OSM data now.

see 
http://apps.sourceforge.net/mediawiki/gpsdrive/index.php?title=Marine_Howto
  (please help improve the wiki page!)

http://grass.osgeo.org/wiki/BSB_data
http://grass.osgeo.org/wiki/S-57_data#libS52
http://openev.cvs.sourceforge.net/openev/contrib/S52/


the very tricky bit is choosing which layers to include. the S-52
gives recommendations of which features to display based on map
scale class, I'd say reuse those. But you would have to enter
that data by hand. If someone provides a list of layernames
per scale band, I might do the rest.

----------------------------------
response: me, requesting a tutorial to review the material.
---------------------------------------------------
response: Hamish
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see SCAMAX and SCAMIN entries in the libS52 CVS file doc/att.txt,

for each token these control which map scales (e.g. 1:25,000-1:100,000)
the feature should be rendered.

and read through the remarks in S52CS.c in the libS52 source
// S52CS.c : Conditional Symbologie procedure 3.2 (CS)

(ignore the code, just look at the comments...)

and the IHO PDF spec docs,
http://grass.osgeo.org/wiki/S-57_data#GRASS_S-52_interface_for_rendering_S-57_data

and you may see why I defer :). It's all there & coded, but a bit daunting
to me.

My idea is a little wrapper C program around S52CS.c to export tokens
based on a list of scales would help us make a table which we could use
in developing the list of layers for the WMS request.

------------------------------
since qgis is used extensively in preparing maps for gpsdrive and there is 
significant interest wrt marine navigation where most charts are S-57 vectors 
the long term goal (very long term) is to move toward a plugin for qgis to 
manipulate the data in order to make it available to gpsdrive. However its a 
bit of a challenge as you can see, I'm not a developer, rather just a listee 
with sailboat so I keep interested in this stuff. 


> - I believe Qgis doesn't use the S57 sublayers and that's why nothing gets
> displayed. Is there any chance that I am right? If I am right,

Your most likely correct. 

> I would like 
> to help with the implementation for this kind of problem. Can anyone in the
> dev team give me directions on where to begin (I have spent some time in
> the source and API of both Qgis and GDAL and feel I can contribute here...)

Perhaps a good start would be reviewing the submitted material above and then 
following the directions and advice of the qgis development team. 

Best of luck

/ch