[gdal-dev] Call for discussion on RFC 64: Triangle, Polyhedral surface and TIN
Rahkonen Jukka (MML)
jukka.rahkonen at maanmittauslaitos.fi
Wed Dec 7 03:03:39 PST 2016
Perhaps some problem with markup, the WKT dows show in Nabble http://osgeo-org.1560.x6.nabble.com/gdal-dev-Call-for-discussion-on-RFC-64-Triangle-Polyhedral-surface-and-TIN-tc5298840.html
MULTIPOLYGON ((( 553 352, 327 363, 442 486, 553 352 )), (( 327 363, 553 352, 422 186, 327 363 )))
Even Rouault wrote:
Re: [gdal-dev] Call for discussion on RFC 64: Triangle, Polyhedral surface and TIN
On mercredi 7 décembre 2016 02:01:54 CET jratike80 wrote:
> Even Rouault-2 wrote
> > Hi,
> > This is a call to discuss the proposed RFC 64: Triangle, Polyhedral
> > surface and TIN
> > https://trac.osgeo.org/gdal/wiki/rfc64_triangle_polyhedralsurface_tin
> > ~~~~~
> I am wondering this part:
> "GEOS methods are still used in some cases, but with the following
> limitations - a Triangle is converted to a Polygon with one exterior ring;
> Polyhedral Surfaces and Triangulated Surfaces are converted to
> MultiPolygons?. (each Triangle in a Triangulated Surface is converted to a
> Polygon as described previously)"
> Does it mean presenting a TIN with two triangles as something like
Something missing here, but I guess you meant as a multipolygon made of 2 polygons ?
> As far as I know such multipolygon is not valid accorfing to the Simple
> feature specification where "boundaries and may touch at only a finite
> number of Points". Valid presentation would probably be to wrap polygons
> into GeometryCollection. Is GEOS used in a relaxed way so that shared parts
> of boundaries in MultiPolygons do not throw an error?
That's a very good remark. Indeed for GEOS purposes, a MultiPolygon with Polygons that have shared boundaries is invalid. I've changed that to a GeometryCollection. But anyway, TIN & PoyhedralSurface in GEOS world are degraded cases where behaviour will always be suboptimal.
Thanks for the feedback.
Spatialys - Geospatial professional services
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