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List: postgis-users
Subject: [postgis-users] st_concavehull
From: Roger Edmunds <rae212a () yahoo ! co ! uk>
Date: 2014-12-14 20:43:22
Message-ID: 1589168082.639038.1418589802972.JavaMail.yahoo () jws11120 ! mail ! ir2 ! yahoo ! com
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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.
[Attachment #5 (text/html)]
<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>
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