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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>+1 <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><div><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in'><p class=MsoNormal style='margin-left:.5in'><b><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>From:</span></b><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'> postgis-devel [mailto:postgis-devel-bounces@lists.osgeo.org] <b>On Behalf Of </b>Paul Ramsey<br><b>Sent:</b> Tuesday, February 07, 2017 9:02 PM<br><b>To:</b> PostGIS Development Discussion <postgis-devel@lists.osgeo.org><br><b>Subject:</b> Re: [postgis-devel] RFC - Orientation checking and forcing functions<o:p></o:p></span></p></div></div><p class=MsoNormal style='margin-left:.5in'><o:p> </o:p></p><div><p class=MsoNormal style='margin-left:.5in'>+1 from me<br><br>P.<o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:0in;margin-right:0in;margin-bottom:12.0pt;margin-left:.5in'><br>On Feb 7, 2017, at 4:55 PM, Daniel Baston <<a href="mailto:dbaston@gmail.com">dbaston@gmail.com</a>> wrote:<o:p></o:p></p></div><blockquote style='margin-top:5.0pt;margin-bottom:5.0pt'><div><div><div><p class=MsoNormal style='margin-left:.5in'>Hi All,<o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'><o:p> </o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'>I put together a pull request a couple of weeks ago that introduces four functions for checking and forcing geometry orientation. The intent is to provide a less-ambiguous alternative to ST_ForceRHR, and an alternative to ST_Orientation that does not depend on SFCGAL. Strk asked that I bring this up on the devel list for a review of the semantics.<o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'><o:p> </o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'>The four proposed functions are.<o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'><o:p> </o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'>ST_ForceCW<o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'>ST_ForceCCW<o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'>ST_IsCW<o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'>ST_IsCCW<o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'><o:p> </o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'>The semantics are straightforward, in my opinion:<o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'><o:p> </o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'>1. ST_ForceCW is a synonym for ST_ForceRHR, which gives all exterior rings a clockwise orientation and all interior rings a counterclockwise orientation. Non-polygonal geometries, including closed LineStrings, are simply passed through.<o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'>2. ST_ForceCCW is simply a shorthand for ST_Reverse(ST_ForceCW)<o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'>3. ST_IsCW returns true if a geometry would not be modified by ST_ForceCW. It is essentially a synonym for ST_OrderingEquals(geom, ST_ForceCW(geom)).<o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'>4. ST_IsCCW returns true if a geometry would not be modified by ST_ForceCCW.<o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'><o:p> </o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'>A few notes:<o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'><o:p> </o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'>ST_IsCW and ST_IsCCW both return false if a polygon has invalid ring orientation (i.e., exterior and interior rings are all clockwise)<o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'>ST_IsCW and ST_IsCCW both return true for geometries that have no non-empty polygonal components.<o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'><o:p> </o:p></p></div><div><div><p class=MsoNormal style='margin-left:.5in'>Relevant links: <o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'>PR: <a href="https://github.com/postgis/postgis/pull/122">https://github.com/postgis/postgis/pull/122</a><o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'>Trac: <a href="https://trac.osgeo.org/postgis/ticket/3689">https://trac.osgeo.org/postgis/ticket/3689</a>, <a href="https://trac.osgeo.org/postgis/ticket/3651">https://trac.osgeo.org/postgis/ticket/3651</a><o:p></o:p></p></div></div><div><p class=MsoNormal style='margin-left:.5in'><o:p> </o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'>Dan<o:p></o:p></p></div></div></div></blockquote><blockquote style='margin-top:5.0pt;margin-bottom:5.0pt'><div><p class=MsoNormal style='margin-left:.5in'>_______________________________________________<br>postgis-devel mailing list<br><a href="mailto:postgis-devel@lists.osgeo.org">postgis-devel@lists.osgeo.org</a><br><a href="https://lists.osgeo.org/mailman/listinfo/postgis-devel">https://lists.osgeo.org/mailman/listinfo/postgis-devel</a><o:p></o:p></p></div></blockquote></div></body></html>