<html><body><div style="color:#000; background-color:#fff; font-family:HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, Sans-Serif;font-size:16px"><div id="yui_3_16_0_1_1418586967041_2641"><br></div><div id="yui_3_16_0_1_1418586967041_2641"><br></div><div id="yui_3_16_0_1_1418586967041_2641" dir="ltr">I've been using postgis for a while now but am now trying to use st_concavehull for the first time and I'm having some issues. In the end I started running the examples in the documentation and I'm still having difficulties. </div><div id="yui_3_16_0_1_1418586967041_2641" dir="ltr"><br></div><div id="yui_3_16_0_1_1418586967041_2641" dir="ltr">Using the "L" shape example in the documentation I tried a range of different target_percent values in PgAdmin using a query like this:</div><div id="yui_3_16_0_1_1418586967041_2641" dir="ltr"> "SELECT st_dumppoints(ST_ConcaveHull(ST_Collect(geom),0.97))FROM l_shape;" . </div><div id="yui_3_16_0_1_1418586967041_2641" dir="ltr"><span style="font-size: 16.3636360168457px;" class=""><br></span></div><div id="yui_3_16_0_1_1418586967041_2641" dir="ltr"><span style="font-size: 16.3636360168457px;" class="" id="yui_3_16_0_1_1418586967041_5859">It seems that going below a value of 0.98 for the target_percent does not make any difference to the output.</span></div><div id="yui_3_16_0_1_1418586967041_2641" dir="ltr"><span style="font-size: 16.3636360168457px;" class="" id="yui_3_16_0_1_1418586967041_6356"> When running in PgAdmin, with a target_percent of 0.98 or less, as well as the output always being the same, a notice is raised, the first line of which says:</span></div><div id="yui_3_16_0_1_1418586967041_2641" dir="ltr"><span style="font-size: 16.3636360168457px;" class="" id="yui_3_16_0_1_1418586967041_11719"> "NOTICE: gserialized_gist_joinsel: jointype 1 not supported".</span></div><div id="yui_3_16_0_1_1418586967041_2641" dir="ltr"><span style="font-size: 16.3636360168457px;" class=""><br></span></div><div id="yui_3_16_0_1_1418586967041_2641" dir="ltr"><span style="font-size: 16.3636360168457px;" class="" id="yui_3_16_0_1_1418586967041_11721"> To check the output I looked at the output with Qgis and it seems there are just three steps in the output.</span></div><div id="yui_3_16_0_1_1418586967041_2641" dir="ltr"><span style="font-size: 16.3636360168457px;" class=""><br></span></div><div id="yui_3_16_0_1_1418586967041_2641" dir="ltr"><span style="font-size: 16.3636360168457px;" class="" id="yui_3_16_0_1_1418586967041_6989">1) From 1.0 down to 0.99999999999999995 the output is the same as the output from st_convexhull.</span></div><div id="yui_3_16_0_1_1418586967041_2641" dir="ltr"><span style="font-size: 16.3636360168457px;" class="" id="yui_3_16_0_1_1418586967041_7697">2) From 0.99999999999999994 down to 0.98000000000000004 the output is as per the picture in the documentation for a target_percent of 0.99.</span></div><div id="yui_3_16_0_1_1418586967041_2641" dir="ltr"><span style="font-size: 16.3636360168457px;" class="" id="yui_3_16_0_1_1418586967041_9226">3) From </span><span style="font-size: 16.3636360168457px;" class="" id="yui_3_16_0_1_1418586967041_10046">0.98000000000000003 and all values below the output is as per the picture </span><span style="font-size: 16.3636360168457px;" class="" id="yui_3_16_0_1_1418586967041_10867">in the documentation for a target_percent of 0.80 and the notice, mentioned above, is displayed in PgAdmin.</span></div><div id="yui_3_16_0_1_1418586967041_2641" dir="ltr"><span style="font-size: 16.3636360168457px;" class=""><br></span></div><div id="yui_3_16_0_1_1418586967041_2641" dir="ltr"><span style="font-size: 16.3636360168457px;" class="" id="yui_3_16_0_1_1418586967041_12596">Unless I am really misunderstanding st_concavehull this is not the behaviour I would expect. Does anyone have any suggestions as to what I may be doing wrong?</span></div><div id="yui_3_16_0_1_1418586967041_2641" dir="ltr"><span style="font-size: 16.3636360168457px;" class=""><br></span></div><div id="yui_3_16_0_1_1418586967041_2641" dir="ltr"><span style="font-size: 16.3636360168457px;" class=""> </span></div><div class="" style="" id="yui_3_16_0_1_1418586967041_5860" dir="ltr"><span style="font-size: 16.3636360168457px;" class="" id="yui_3_16_0_1_1418586967041_13566">I am using:</span></div><div class="" style="" id="yui_3_16_0_1_1418586967041_5860" dir="ltr">PostgreSQL 9.3.5 on i686-pc-linux-gnu, compiled by gcc (Ubuntu 4.8.2-19ubuntu1) 4.8.2, 32-bit<br class="" style=""></div><div class="" style="" id="yui_3_16_0_1_1418586967041_5860" dir="ltr">and </div><div id="yui_3_16_0_1_1418586967041_2641" dir="ltr">POSTGIS="2.1.2 r12389" GEOS="3.4.2-CAPI-1.8.2 r3921" PROJ="Rel. 4.8.0, 6 March 2012" GDAL="GDAL 1.10.1, released 2013/08/26" LIBXML="2.9.1" LIBJSON="UNKNOWN" RASTER<br></div><div id="yui_3_16_0_1_1418586967041_2641" dir="ltr"><br></div><div id="yui_3_16_0_1_1418586967041_2641" dir="ltr">I have tried this on Windows 7 and Ubuntu 14.04LTS with the same results.</div><div id="yui_3_16_0_1_1418586967041_2641" dir="ltr" class="" style=""><br class="" style=""></div></div></body></html>