Hi, 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 ))) -Jukka- 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. Even -- Spatialys - Geospatial professional services http://www.spatialys.com
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