[gdal-dev] Ring orientation in polygons

[Frank Warmerdam]

Tim Mitchell wrote:
> Hi,
> 
> I know the OpenGIS standard says the the exterior linear ring of a 
> polygon is oriented clockwise and the interior rings are 
> counterclockwise.  I also know that no all data does this.
> 
> I was just wondering if I can rely on an OGRPolygon object adhering to 
> the OpenGIS standard even if the underlying data doesn't, or if I need 
> to check the isClockwise() value on each ring I obtain from a polygon?

Tim,

Currently OGRPolygon does not enforce winding order, and you cannot
depend on polygons returned by drivers having any particular winding
order.

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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