Re: [Geojson] Question regarding RFC 7946: Interior and Exterior Linear Rings
Sean Gillies <sean.gillies@gmail.com> Tue, 23 May 2017 10:16 UTC
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From: Sean Gillies <sean.gillies@gmail.com>
Date: Tue, 23 May 2017 12:16:22 +0200
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To: Chris Goodman <Chris.Goodman@objectconsulting.com.au>
Cc: "geojson@ietf.org" <geojson@ietf.org>
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Subject: Re: [Geojson] Question regarding RFC 7946: Interior and Exterior Linear Rings
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Hi Chris, On Tue, May 23, 2017 at 9:19 AM, Chris Goodman < Chris.Goodman@objectconsulting.com.au> wrote: > Polygons with more than one of these rings, the first MUST be > > the exterior ring, and any others MUST be interior rings. The > > exterior ring bounds the surface, and the interior rings (if > > present) bound holes within the surface. > > > > > > Q1. If an interior linear ring (hole) is not completely inside the > exterior ring (border) of a polygon, is it an illegal polygon? > > > GeoJson.io allows such an interior ring to be imported. Perhaps it is a > bug. > It would be invalid from an OGC simple features perspective but is not invalid GeoJSON. > > > Q2. If the interior ring is not clockwise, then what is the expected > behaviour of the polygon? > The same. > > > Q3. Should ‘interior linear ring’ and ‘exterior linear ring’ be formally > defined in the RFC? > The WG didn't find this necessary. Are you saying it would improve the spec? How so? > > > Q4. If two interior linear rings overlap, then is the result the union of > the two holes? > Geometric operations are outside the scope of the GeoJSON. The format only describes a serialization for polygons. Exterior ring comes first, interior rings follow. >From a OGC simple features perspective a polygon with overlapping holes is invalid, but I've found that GIS software often has fault-tolerant modes that can deal with these kinds of invalid shapes. PostGIS's buffer(0.0), for example, which I expect would indeed replace the overlapping holes with a single hole that is their union, and not create any "anti-holes" or new positive areas. -- Sean Gillies
- [Geojson] Question regarding RFC 7946: Interior a… Chris Goodman
- Re: [Geojson] Question regarding RFC 7946: Interi… Sean Gillies
- Re: [Geojson] Question regarding RFC 7946: Interi… Carl Reed