[Geojson] handedness of polygons

Sean Gillies sgillies at frii.com
Sun Mar 30 20:18:43 PDT 2008

John R. Frank wrote:
> Does GeoJSON offer a way of indicating whether a polygon is clockwise or
> counter-clockwise?  Forgive me if this is in a wiki somewhere; I haven't
> found it yet.
> While not all clients are sophisticated enough to make well-defined
> polygons that have an unambiguous "inside" and "outside", displaying data
> properly across the dataline or the poles requires well-defined
> orientation.  So, it would be good if geojson enabled representation of
> such information.
> On the same note, has anyone found a good discussion of orientation issues
> in KML for Google Earth?
> Thanks,
> John

I don't know about a single entry point into good discussions, but
here's discussion of one issue:


For KML (and GML too), the orientation of polygon faces with respect to
the order of ring vertices follows the right-hand rule. If you want
Google Earth to render your polygons with 3D effects properly, you need
to write out positions in counter-clockwise order.


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