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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link="#0563C1" vlink="#954F72"><div class=WordSection1><p class=MsoNormal><span style='color:#1F497D'>Jakob,<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Did you upgrade your install from an older version say 9.4.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>I think if you did a pg_upgrade, and didn't do a ALTER EXTENSION postgis… after upgrade, this would explain your issue since the operators would not get upgraded.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>On my PostGIS 2.3.2, 9.6 behavior is as expected. Unfortunately I don't have 2.2.2 lying around at moment.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Also there was an ordering bug I think in 2.2 early version that may have caused this. If that is your issue, then output of <-> would be real even though ordering is wrong.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Try this query:<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>SELECT id,<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'> ST_Distance(my_point.geom, <o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'> my_polygons.geom) AS real_distance,<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'> ST_Distance(my_point.geom, <o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'> ST_Centroid(my_polygons.geom)) AS centroid_distance, my_point.geom <-> my_polygons.geom <o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>FROM (<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'> SELECT 'blue' AS id, ST_Polygon(ST_GeomFromText('LINESTRING(0 3, 2 3, 2 4, 0 4 ,0 3)'),4326) AS geom<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'> UNION<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'> SELECT 'green' AS id, ST_Polygon(ST_GeomFromText('LINESTRING(2 0, 8 0 , 8 2, 2 2 ,2 0)'),4326) AS geom<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>) AS my_polygons,<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>(<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'> SELECT ST_SetSRID(ST_Point(1, 1),4326) AS geom<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>) AS my_point<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>ORDER BY my_point.geom <-> my_polygons.geom<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>-- output should be --<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'> id | real_distance | centroid_distance | ?column?<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>-------+---------------+-------------------+----------<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'> green | 1 | 4 | 1<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'> blue | 2 | 2.5 | 2<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>(2 rows)<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Hope that helps,<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Regina<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><a href="http://postgis.us">http://postgis.us</a><o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><a href="http://www.paragoncorporation.com">http://www.paragoncorporation.com</a><o:p></o:p></span></p><p class=MsoNormal><span style='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>From:</b> postgis-users [mailto:postgis-users-bounces@lists.osgeo.org] <b>On Behalf Of </b>Jakob Miksch<br><b>Sent:</b> Thursday, July 13, 2017 4:27 AM<br><b>To:</b> postgis-users@lists.osgeo.org<br><b>Subject:</b> [postgis-users] <-> operator does not return true distance<o:p></o:p></p></div></div><p class=MsoNormal style='margin-left:.5in'><o:p> </o:p></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB>Hi, <o:p></o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB><o:p> </o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB>(I asked a similar question here <a href="https://gis.stackexchange.com/questions/247034/postgis-operator-does-not-return-true-distance">https://gis.stackexchange.com/questions/247034/postgis-operator-does-not-return-true-distance</a> )<o:p></o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB><o:p> </o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB>I used the <-> operator with PostGIS 2.2.2 and PostgreSQL 9.5.7 .<o:p></o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB><o:p> </o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB>According to the docs (<a href="http://postgis.net/docs/manual-2.2/geometry_distance_knn.html">http://postgis.net/docs/manual-2.2/geometry_distance_knn.html</a>) the <-> operator should order by "true KNN distance" and *not* by "centroid distance". <o:p></o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB><o:p> </o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB>However it does not work for me. See the minimal example below: <o:p></o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB>( illustration: <a href="https://i.stack.imgur.com/QZA6D.png">https://i.stack.imgur.com/QZA6D.png</a> )<o:p></o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB><o:p> </o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB>SELECT id,<o:p></o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB> ST_Distance(my_point.geom, <o:p></o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB> my_polygons.geom) AS real_distance,<o:p></o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB> ST_Distance(my_point.geom, <o:p></o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB> ST_Centroid(my_polygons.geom)) AS centroid_distance<o:p></o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB><o:p> </o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB>FROM (<o:p></o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB> SELECT 'blue' AS id, ST_Polygon(ST_GeomFromText('LINESTRING(0 3, 2 3, 2 4, 0 4 ,0 3)'),4326) AS geom<o:p></o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB> UNION<o:p></o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB> SELECT 'green' AS id, ST_Polygon(ST_GeomFromText('LINESTRING(2 0, 8 0 , 8 2, 2 2 ,2 0)'),4326) AS geom<o:p></o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB><o:p> </o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB>) AS my_polygons,<o:p></o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB><o:p> </o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB>(<o:p></o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB> SELECT ST_SetSRID(ST_Point(1, 1),4326) AS geom<o:p></o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB>) AS my_point<o:p></o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB><o:p> </o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB>ORDER BY my_point.geom <-> my_polygons.geom <o:p></o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB><o:p> </o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB><o:p> </o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB>--- obtained Result:<o:p></o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB><o:p> </o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB><o:p> </o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB>| | real_distance | centroid_distance |<o:p></o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB>---------------------------------------------<o:p></o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB>| blue | 2 | 2.5 |<o:p></o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB>| green | 1 | 4 |<o:p></o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB><o:p> </o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB>(I expected the rows to be in the opposite order)<o:p></o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB><o:p> </o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB>Apparently the <-> operator orders by the centroid_distance and not by the real_distance, even though the docs say: "[...] for PostgreSQL 9.5+, does true KNN distance search giving true distance between geometries [...]"<o:p></o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB><o:p> </o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB>I tried the same example on 2.3.2 and PostgreSQL 9.5.7 and I get the expected result (which orders by "real_distance").<o:p></o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB><o:p> </o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB>So, for me it seems that ordering by "real_distance" with the <-> operator does not work with PostGIS 2.2.2 - but this is *not* written in the docs.<o:p></o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB><o:p> </o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB>Can you reproduce this behaviour? Or did I understand/make something wrong here?<o:p></o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=EN-GB><o:p> </o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=NO-BOK>Thanks and best regards,<o:p></o:p></span></p><p class=MsoNormal style='margin-left:.5in'><span lang=NO-BOK>Jakob<o:p></o:p></span></p></div></body></html>