[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


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 d├ęcembre 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



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