[postgis-users] st_concavehull

[Roger Edmunds]

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. 
Using the "L" shape example in the documentation I tried a range of different target_percent values in PgAdmin using a query like this: "SELECT  st_dumppoints(ST_ConcaveHull(ST_Collect(geom),0.97))FROM l_shape;" . 
It seems that going below a value of 0.98 for the target_percent does not make any difference to the output. 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: "NOTICE:  gserialized_gist_joinsel: jointype 1 not supported".
 To check the output I looked at the output with Qgis and it seems there are just three steps in the output.
1) From 1.0 down to 0.99999999999999995 the output is the same as the output from st_convexhull.2) From 0.99999999999999994 down to 0.98000000000000004 the output is as per the picture in the documentation for a target_percent of 0.99.3) From 0.98000000000000003 and all values below the output is as per the picture in the documentation for a target_percent of 0.80 and the notice, mentioned above, is displayed in PgAdmin.
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?
 I am using:PostgreSQL 9.3.5 on i686-pc-linux-gnu, compiled by gcc (Ubuntu 4.8.2-19ubuntu1) 4.8.2, 32-bit
and 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

I have tried this on Windows 7 and Ubuntu 14.04LTS with the same results.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/postgis-users/attachments/20141214/14b2dd62/attachment.html>