[gdal-dev] Call for discussion on RFC 49: Curve geometries

Paul Ramsey pramsey at cleverelephant.ca
Wed Nov 5 09:40:38 PST 2014

My only concern/note here is with regard to the WKB type numbers for features with a Z. The RFC seems to say that the numbers for the curve types will be ISO numbers, while the numbers for the old SFS types will be the backwards compatible ones. This puts OGR into an ugly snaggletooth situation, where the WKB emitted is not really consistent. In some ways it’s worse than PostGIS… 

I feel like the best bet is to be consistent, but provide two consistent modes

- ISO mode, using the ISO defined type numbers for *all* types/dimensionalities
- Backwards/OGC mode, using the old wkb25DBit mask for all types.

Of course, I could be wrong, maybe a snaggletooth is better, but it doesn’t pass the smell test for me


Paul Ramsey

On November 5, 2014 at 7:01:32 AM, Even Rouault (even.rouault at spatialys.com) wrote:


This is a call for discussion on RFC 49: Curve geometries  


Below the summary :  
The current geometry model in GDAL 1.X makes use of points, lines, polygons  
and aggregations of them (multipoints, multilines, multipolygons and geometry  
collections). It was modeled from the geometry class hierarchy of the  
"OpenGIS Simple Feature Access Part 1 : Common Architecture" (in its 1.1.0  

This RFC covers the addition of new geometry types that have been added in  
ISO/IEC 13249 Part 3 Spatial (abreviated as ISO SQL/MM Part 3):  
* circular string: a circular arc, or a sequence of connected circular arcs,  
each of them describe by 3 points: the first point of the arc, an  
intermediate point and the final point  
* compound curve: a sequence of connected curves, either line strings or  
circular strings  
* curve polygon: polygon consisting of one outer ring, and zero or more  
inner ring. Each ring can be one of the curve implementations: line  
strings, circular strings, compound curves.  
* multicurve: a collection of curves (line strings, circular strings,  
compound curves)  
* multisurface: a collection of surfaces (polygons, curve polygons)  

The scope of this RFC consists in :  
* adding the new geometry classes to the existing geometry class hierarchy,  
with the corresponding importer and exporter of WKT (Well Known Text) and  
WKB (Well Known Binary) encodings  
* adding methods to convert those curve geometries into their approximated  
linear version, and to do the reverse operation  
* upgrading some of the drivers that can support such geometries : GML (and  
indirectly NAS, WFS), PostGIS/PGDump, GeoPackage, SQLite, CSV, VRT.  

Have a good reading,  


Spatialys - Geospatial professional services  
gdal-dev mailing list  
gdal-dev at lists.osgeo.org  
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