[geos-devel] Ring winding?

[Martin Davis]

>   1. Do the exterior and interior rings still differ in winding?  Or
are they all the same winding?

In JTS/GEOS any orientation (winding) of the rings is allowed.

>   2. Is each ring closed with a redundant point?

Yes.

Martin Davis, Senior Technical Architect
Vivid Solutions Inc.
Suite #1A-2328 Government Street Victoria, B.C. V8T 5G5
Phone: (250) 385 6040 - Local 308 Fax: (250) 385 6046


> -----Original Message-----
> From: Ben Discoe [mailto:ben at vterrain.org] 
> Sent: Friday, February 27, 2004 1:23 PM
> To: 'GEOS Development List'
> Subject: [geos-devel] Ring winding?
> 
> 
> 
> I have a somewhat general question about how GEOS stores its polygons.
> 
> In the 'old' GIS style, ala ESRI Shapefile, the polygon 
> consists of a single set of points, where the exterior ring 
> has a counter-clockwise winding, and the interior rings have 
> a clockwise winding.  Each ring is also closed (first point 
> is duplicated as the last) so that mathematically, the entire 
> set of points can be rendered as a single polygon without 
> knowledge of rings at all.
> 
> In the 'new' OGC style of separate rings, ala JTS/GEOS:
>   1. Do the exterior and interior rings still differ in 
> winding?  Or are they all the same winding?
>   2. Is each ring closed with a redundant point?
> 
> -Ben
> 
> _______________________________________________
> geos-devel mailing list
> geos-devel at geos.refractions.net 
> http://geos.refractions.net/mailman/listinfo/geos-devel
>