[postgis-devel] topology : finding if the ring is an inner ring or outer ring
remi.cura at gmail.com
Fri Feb 20 02:26:16 PST 2015
I wanted to avoid the computing of winding.
But now I doubt it is possible.
Instead of winding I chose to compute signed area, because I'm afraid
robust winding may be difficult.
As a workaround, I wrote a function
compute the signed area of a ring,
and that is robust to precision issue.
Now I still have trouble getting the correct ring because the function
topology.getRingEdge doesn't return the correct ring in one case.
I do have a workaround for this, which I will attach to the ticket.
2015-02-20 10:11 GMT+01:00 Sandro Santilli <strk at keybit.net>:
> On Thu, Feb 19, 2015 at 07:04:44PM +0100, Rémi Cura wrote:
> > Hello,
> > somebody knows how to find the information?
> > I can't find something that will reliabily work with flat ring.
> Get on the side of the edge where the face you're interested in is found.
> Walk on that side of the edge until you end back to where you started
> (follow the first edge direction if on its left, opposite direction
> Compute winding of the resulting ring.
> An inner ring of the face in object would be ordered counterclockwise.
> The shell would be clockwise.
> Sent from our free software
> postgis-devel mailing list
> postgis-devel at lists.osgeo.org
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