[postgis-devel] RFC - Orientation checking and forcing functions

Daniel Baston dbaston at gmail.com
Wed Feb 8 12:35:05 PST 2017


I'll try to see if I can come up with a less ambiguous name, without
resorting to
ST_ForcePolygonsClockwiseExteriorRingAndCounterClockwiseInteriorRings, but
I'll also note that the proposed terminology has been used by PostGIS
internally since 2010:

https://github.com/postgis/postgis/commit/2d07d7eb59d2bb8db9d4773cd84619cd696bc471

Dan


On Wed, Feb 8, 2017 at 3:17 PM, Sandro Santilli <strk at kbt.io> wrote:

> On Wed, Feb 08, 2017 at 03:05:33PM -0500, Daniel Baston wrote:
> > The idea was that adding functions with different names would be helpful,
> > because "RHR" and "LHR" mean different things to different people (and
> > therefore don't mean much of anything.)
>
> In PostGIS "RHR" and "LHR" have well-documented meaning, right ?
>
> > See, for example, the fourth bullet under
> > https://tools.ietf.org/html/rfc7946#section-3.1.6
>
> The Wikipedia definition of the rule is about 3d and implies a 3D space,
> which is not always the case within PostGIS geometries:
> https://en.wikipedia.org/wiki/Right-hand_rule
>
> If you find a name/label which means the same to everybody I'll be
> happy to see a wrapper function using it. "Clockwise" for a polygon
> with holes doesn't seem to be unambiguous to me (it could for example
> mean "all rings are clockwise"...)
>
> --strk;
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