[Gdal-dev] s-57 to vrml elevation map?

[s duclos]

--- Frank Warmerdam <warmerdam at pobox.com> wrote:
> Thorsten Röllich wrote:
> > Hello,
> > 
> > I'm building a 3D model of a coastal area in
> Germany and try to use S-57 datasets as a source.
> > First I used the program SeeMyDEnc from sevencs to
> open my datasets and it looked fine. By picking a
> position on the map, the program shows the primitive
> DEPARE (Depth Area Group) and the corresponding
> depth (DRVAL1 and DRVAL2).
> > This seems to be enough information for modeling a
> (rough) topography.
> > So I looked for a converter, that fits my needs...
> (Something, that converts S-57 to VRML elevation map
> would be ideal)
> > What I found was the ogr library and the tools
> ogrinfo and ogr2ogr.
> > So I will have to write the converter myself..
> > The plan was to translate S-57 to GML (which is
> more human readable) using ogr2ogr and parse all
> Polygons that describe an Area and the corresponding
> depth. 
> > The  translation to GML worked fine, but I could
> not find any depth information in the file. I tried
> it with many ogr2ogr options, but the 3rd dimension
> seems always to be lost.
> > 
> > Does anybody have an idea how to translate the
> topographic information from S-57 files to an
> elevation map, or how to extract the polygons and
> the depth of DEPARE fields?
> > Very thankful for any hints on this. Kindest
> regards / Thorsten
> 
> Thorsten,
> 
> Based on your email I did a test conversion of some
> features types from
> S-57 to GML and discovered some serious holes in my
> support for 3D GML and
> GML "geometry collection" types of geometries.  I
> have committed patches
> for that back to GDAL/OGR.  I think it may have been
> responsible for some
> of your problems.
> 
> Now, for instance, the SOUNDG feature class comes
> through in GML as a
> MultiPoint collection of 3D points.
> 
> However, for features classes like DEPARE, the
> elevation is only found in
> the attributes.  In the case of DEPARE there are
> DRVAL1 and DRVAL2 attributes
> which appear to be the minimum and maximum depth
> values in the area.
> 
> I don't know what language you were looking to
> implement the VRML writing
> in, but if you want to do it in C, C++ or Python why
> not just use the
> OGR API to read the objects and then concentrate on
> writing the VRML?
> 
> As far as I know (and I am unfortunately no expert)
> the S-57 data will just
> have the depth areas with depth ranges over the
> whole polygon, and the sounding
> point values.  I don't know the best way of turning
> this into some sort of
> mesh or whatever you need in VRML.  Perhaps you
> would be best off just applying
> a point interpolator to the soundings and ignoring
> the DEPAREs?

Hi,

I would like to add to Frank that DEPARE are used
for geometric primitives AREA and LINE. The latter are
in fact isobath.

You can check at www.s-57.com the catalog of object
class and attribute. For example the attribute DRVAL1
is used in 16 objects (DEPARE been one of them.)


Hope this help,

Sylvain.

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