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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'>ST_Distance existed before we had <->. <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><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>If you are using PostgreSQL 9.5+ with PostGIS 2.2, you can just stick with using <->, but note that it doesn't always use and index. <-> only uses and index when it is in the ORDER BY clause and one side is a constant geometry (which you can achieve even when you don't have a constant by using a LATERAL clause).<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><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>In the case of geography though <-> will always give the sphere distance, while ST_Distance by default gives the spheroid distance. So ST_Distance is slightly more accurate to use for geography.<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><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>We accept patches on documentation BTW. <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><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><div style='border:none;border-left:solid blue 1.5pt;padding:0in 0in 0in 4.0pt'><div><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in'><p class=MsoNormal><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-users [mailto:postgis-users-bounces@lists.osgeo.org] <b>On Behalf Of </b>Eric St-Georges<br><b>Sent:</b> Monday, November 12, 2018 4:47 PM<br><b>To:</b> postgis-users@lists.osgeo.org<br><b>Subject:</b> [postgis-users] ST_DWithin, ST_Distance and <-><o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><div><p class=MsoNormal>Hi,<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>Looking for official documentation or guidance regarding the usage of ST_DWithin, ST_Distance and <->, especially when it comes to using indices. For example, the <a href="https://postgis.net/docs/ST_Distance.html">ST_Distance page</a> itself doesn't mention that the function will not use indices.<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>For example: <o:p></o:p></p></div><div><p class=MsoNormal>If I want to get the closest point to another, why can't ST_Distance use an index, but <-> can?<o:p></o:p></p></div><div><p class=MsoNormal>Is there anyway to get a distance in meters or some other unit from the <-> operator on geography types?<o:p></o:p></p></div><div><p class=MsoNormal>if ST_DWithin and <-> and other similar functions/operators should be used when dealing with distance, what's the use case for ST_Distance?<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>Regards,<o:p></o:p></p></div><div><p class=MsoNormal>Eric St-Georges<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div></div></div></body></html>