[OSM-dev] Algorithm help

Richard Duivenvoorde rdmailings at duif.net
Wed May 28 21:35:14 BST 2008

Richard Fairhurst wrote:
> Can anybody point me in the direction of an algorithm that will  
> determine whether a closed way (polyline) is clockwise or anti- 
> clockwise?
> cheers
> Richard
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> dev at openstreetmap.org
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there is a good set of (explanations of) algorithms here:


There is no copy and paste code there, but the explanation how to do it 
in "Subject 2.07: How do I find the orientation of a simple polygon?" 
can maybe help you further?

Richard Duivenvoorde

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