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

[Thorsten Röllich]

gdal-dev at remotesensing.org schrieb am 22.09.03 16:28:43:


--- 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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Thank You, Frank and Sylvain, for your immediate response.
It's working!
I'm using the multipoints from SOUNDG for water areas,
and  the lines from LNDELV (land elevation) and COALNE (coastline) plus their appropriate elevation for land areas.
Then I use an interpolator for all the points, as Frank proposed.
Thorsten



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