[gdal-dev] Call for discussion on RFC 64: Triangle, Polyhedral surface and TIN

Even Rouault even.rouault at spatialys.com
Tue Dec 6 12:41:28 PST 2016


On mardi 6 d├ęcembre 2016 20:31:57 CET Michael Sumner wrote:
> Thanks Even,
> 
> Does a TriangulatedSurface consist of separate Triangles, all with each
> three vertices stored explicitly? I.e. is there no shared vertex pool that
> primitives use via index?

Yes, the TriangulatedSurface is a collection of separate triangles. No smart optimization here. 
We stick to the simple features model.

> 
> That seems to be what simple features dictates, but it's unclear to me how
> applications should work with it. Is vertex de-duplication to be be done at
> each conversion, or is there a way to carry those indexes through?

Apart from shapefile/filegdb triangle strip/fan that could be considered as a kind of vertex 
indexing, the WKT/WKB representation (and thus the exchanges with PostGIS) don't have 
that.

Actually you could retrieve an indexed view of the TIN by using the 
GDALTriangulationCreateDelaunay() API
( http://www.gdal.org/gdal__alg_8h.html#a498205ae5f4f0ec9f43e5c65bb392060 ), although 
it is a bit overkill to recompute a triangulation from a set of triangles... (and the triangulation 
it will return will generally not be the original one)

Even

> 
> Cheers, Mike
> 
> On Wed, Dec 7, 2016, 03:22 Even Rouault <even.rouault at spatialys.com> 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
> > 
> > 
> > 
> > ~~~~~
> > 
> > 
> > 
> > Summary:
> > 
> > 
> > 
> > As of now, the OGRGeometry class (the base class from which all the
> > subtypes are derived) is limited to OGRCompoundCurve, OGRCircularString,
> > OGRLinearRing, OGRMultiLineString, OGRMultiPoint, OGRMultiPolygon,
> > OGRMultiCurve, OGRSimpleCurve, OGRCurvePolygon and OGRPolygon.
> > 
> > 
> > 
> > This RFC addresses the addition of the following new geometries in
> > OGRGeometry:
> > 
> > * Triangle - A subset of polygons, the fundamental difference is that it
> > is made of 3 nodes only (actually 4, with the last one being the
> > repetition
> > of the first one) and ONLY ONE exterior boundary and NO interior polygons.
> > 
> > * PolyhedralSurface - A 3D figure made exclusively of Polygons.
> > 
> > * TriangulatedSurface - A subset of PolyhedralSurface; a 3D figure which
> > consists exclusively of Triangles.
> > 
> > 
> > 
> > ~~~~~
> > 
> > 
> > 
> > I've rebased and extended the work done by Avyav during last GSoc on top
> > of current trunk, where it passes our continuous integration tests. I
> > think
> > we should consider merging it soon as it can easily rot if kept longer in
> > a
> > branch (the refresh from my previous branch dating to end of August was
> > rather painful)
> > 
> > 
> > 
> > Even
> > 
> > 
> > 
> > --
> > 
> > Spatialys - Geospatial professional services
> > 
> > http://www.spatialys.com
> > _______________________________________________
> > gdal-dev mailing list
> > gdal-dev at lists.osgeo.org
> > http://lists.osgeo.org/mailman/listinfo/gdal-dev


-- 
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