[gdal-dev] Polygon winding order in ogrinfo output

Frank Warmerdam warmerdam at pobox.com
Tue Jun 10 20:18:34 EDT 2008


Roger André wrote:
> Just a quick question to find out how the clockwise winding order is 
> established in ogrinfo output.  Is this because the original data file 
> being read was created with the polygons in that order, or is it a 
> "feature" of ogr's?

Roger,

OGR uses the simple features geometry model which places no requirements
on the winding direction of polygon rings.  So generally speaking the
winding direction is not defined - often it will be whatever was most
convenient when reading from the source files.

The Shapefile *writer* does have to rewind polygon rings to put them into
the required winding order for shapefiles.

Best regards,
-- 
---------------------------------------+--------------------------------------
I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | President OSGeo, http://osgeo.org



More information about the gdal-dev mailing list