[gdal-dev] Performance of reading large polygons with holes

[Even Rouault]

Le samedi 21 avril 2012 12:41:49, Jukka Rahkonen a écrit :
> Hi,
> 
> Martin Davis started this thread on OpenJUMP-dev list
> http://thread.gmane.org/gmane.comp.gis.jump.devel/11119
> Perhaps someone would like to test how OGR performs with such data?
> Link to dataset is mentioned in the discussion.

I suppose that dataset you mention is : 
http://maps.cmparks.net/geoserver/metroparks/ows?service=WFS&version=1.0.0&request=GetFeature&typeName=metroparks:tpi_1&outputFormat=SHAPE-
ZIP ?

If so, on my box, the whole shapefile (~ 390 MB for the .shp / ~1 million 
features) can be read in about 4 seconds with a simplified version of ogrinfo 
that just loops on all the features. The algorithm that assembles the rings of 
polygon shapes into polygons that conform to Simple Features has been pretty 
improved during the last years. It is in the 
OGRGeometryFactory::organizePolygons() method ( see 
http://trac.osgeo.org/gdal/browser/trunk/gdal/ogr/ogrgeometryfactory.cpp#L1015 
) . For shapefiles, there's a shortcut that save a lot of computations w.r.t. 
the general algorithm, because the shapefile specification states that outer 
rings should be described clockwise , whereas inner rings should be described 
counter-clockwise.

> 
> -Jukka Rahkonen-
> 
> 
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