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List: postgis-users
Subject: Re: [postgis-users] duplicated nodes
From: "=?iso-8859-1?Q?Olivier_Lepr=EAtre?=" <o.lepretre () gmail ! com>
Date: 2017-08-03 14:46:30
Message-ID: 001d01d30c67$4d162ca0$e74285e0$ () noetika ! com
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Thanks for this helpful precision/explanation. This function needs to be
known, a bit harsh to understand but many applications for geomatics…
Olivier
De : postgis-users [mailto:postgis-users-bounces@lists.osgeo.org] De la part
de Regina Obe
Envoyé : jeudi 3 août 2017 15:28
À : 'PostGIS Users Discussion' <postgis-users@lists.osgeo.org>
Objet : Re: [postgis-users] duplicated nodes
Ah great. Sorry about forgetting about the over on that one. Glad you
figured it out.
BTW in new docs, I cut in a picture so it's hopeful a bit clearer to folks
what it does. I've got to clean up the formatting a bit.
http://postgis.net/docs/manual-dev/ST_ClusterDBSCAN.html
Thanks,
Regina
http://postgis.us
From: postgis-users [mailto:postgis-users-bounces@lists.osgeo.org] On Behalf
Of Olivier Leprêtre
Sent: Thursday, August 03, 2017 4:07 AM
To: 'PostGIS Users Discussion' <postgis-users@lists.osgeo.org
<mailto:postgis-users@lists.osgeo.org> >
Subject: Re: [postgis-users] duplicated nodes
Thanks very much Regina, it’s exactly what I searched for, it solved me two
problems : false positives and groups display.
Typo : I just added ‘over()’ after ST_ClusterDBSCAN
Olivier
De : postgis-users [mailto:postgis-users-bounces@lists.osgeo.org] De la part
de Regina Obe
Envoyé : mercredi 2 août 2017 23:15
À : 'PostGIS Users Discussion' <postgis-users@lists.osgeo.org
<mailto:postgis-users@lists.osgeo.org> >
Objet : Re: [postgis-users] duplicated nodes
If you are running PostGIS 2.3 or above, I think ST_ClusterDBSCAN might do
the trick for you:
http://postgis.net/docs/manual-2.3/ST_ClusterDBSCAN.html
You can set distance to 0 and minpoints to 2. All points that are not 0
distance from any other point will have NULL in the bucket column.
All other ones that have bucket numbers are duplicated.
So:
SELECT n.code, n.geom, ST_ClusterDBSCAN(n.geom, 0,2) AS bucket
FROM nodes
If you want the counts instead of the bucket, you can do
SELECT o.code, o.geom, COUNT(*) OVER(PARTITION BY bucket) AS npoints,
bucket
FROM (SELECT n.code, n.geom, ST_ClusterDBSCAN(n.geom, 0,2) AS bucket
FROM nodes ) AS o
WHERE bucket IS NOT NULL;
I didn't test so I might have a typo.
Hope that helps,
Regina
From: postgis-users [mailto:postgis-users-bounces@lists.osgeo.org] On Behalf
Of Olivier Leprêtre
Sent: Wednesday, August 02, 2017 3:28 PM
To: postgis-users@lists.osgeo.org <mailto:postgis-users@lists.osgeo.org>
Subject: [postgis-users] duplicated nodes
Hi,
I have a point layer that contains several superposed nodes two, three times
or more. I would like to display each group list and the number of item in
each. I found this query which “works” but returns some false positive
select case when lag(o.geom) OVER (PARTITION BY o.geom) = o.geom then ''
else 'x ' || o.nbre::text end,d.code from
(select geom,count(*) as nbre from nodes group by geom having count(*) >1)
as o,
lateral (select * from nodes) as d where st_within(o.geom,d.geom)
I understand that false positives (yellow beneath) comes from “group by
geom” which use a bounding box and catch close but not duplicated points.
I tried other solutions which all get too complicated with several “join of
join”. I would appreciate if someone has an idea on the top of his/her head
!
Thanks
Olivier
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</o:shapelayout></xml><![endif]--></head><body lang=FR link="#0563C1" \
vlink="#954F72"><div class=WordSection1><p class=MsoNormal><span lang=EN-GB \
style='mso-fareast-language:EN-US'>Thanks for this helpful precision/explanation. \
This function needs to be known, a bit harsh to understand but many applications for \
geomatics…<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB \
style='mso-fareast-language:EN-US'><o:p> </o:p></span></p><p \
class=MsoNormal><span lang=EN-GB \
style='mso-fareast-language:EN-US'>Olivier<o:p></o:p></span></p><p \
class=MsoNormal><span lang=EN-GB \
style='mso-fareast-language:EN-US'><o:p> </o:p></span></p><div><div \
style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0cm 0cm 0cm'><p \
class=MsoNormal><b>De :</b> postgis-users \
[mailto:postgis-users-bounces@lists.osgeo.org] <b>De la part de</b> Regina \
Obe<br><b>Envoyé :</b> jeudi 3 août 2017 15:28<br><b>À :</b> 'PostGIS Users \
Discussion' <postgis-users@lists.osgeo.org><br><b>Objet :</b> Re: \
[postgis-users] duplicated nodes<o:p></o:p></p></div></div><p \
class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><span lang=EN-US \
style='color:#1F497D'>Ah great. Sorry about forgetting about the over on that \
one. Glad you figured it out.<o:p></o:p></span></p><p class=MsoNormal><span \
lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span \
lang=EN-US style='color:#1F497D'>BTW in new docs, I cut in a picture so it's hopeful \
a bit clearer to folks what it does. I've got to clean up the formatting a \
bit.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US \
style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US \
style='color:#1F497D'><a \
href="http://postgis.net/docs/manual-dev/ST_ClusterDBSCAN.html">http://postgis.net/docs/manual-dev/ST_ClusterDBSCAN.html</a><o:p></o:p></span></p><p \
class=MsoNormal><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><p \
class=MsoNormal><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><p \
class=MsoNormal><span lang=EN-US \
style='color:#1F497D'>Thanks,<o:p></o:p></span></p><p class=MsoNormal><span \
lang=EN-US style='color:#1F497D'>Regina<o:p></o:p></span></p><p class=MsoNormal><span \
lang=EN-US style='color:#1F497D'><a \
href="http://postgis.us">http://postgis.us</a><o:p></o:p></span></p><p \
class=MsoNormal><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><p \
class=MsoNormal><span lang=EN-US \
style='color:#1F497D'><o:p> </o:p></span></p><div><div \
style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0cm 0cm 0cm'><p \
class=MsoNormal style='margin-left:36.0pt'><b><span lang=EN-US>From:</span></b><span \
lang=EN-US> postgis-users [<a \
href="mailto:postgis-users-bounces@lists.osgeo.org">mailto:postgis-users-bounces@lists.osgeo.org</a>] \
<b>On Behalf Of </b>Olivier Leprêtre<br><b>Sent:</b> Thursday, August 03, 2017 4:07 \
AM<br><b>To:</b> 'PostGIS Users Discussion' <<a \
href="mailto:postgis-users@lists.osgeo.org">postgis-users@lists.osgeo.org</a>><br><b>Subject:</b> \
Re: [postgis-users] duplicated nodes<o:p></o:p></span></p></div></div><p \
class=MsoNormal style='margin-left:36.0pt'><span \
lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal \
style='margin-left:36.0pt'><span lang=EN-GB>Thanks very much Regina, it’s \
exactly what I searched for, it solved me two problems : false positives and \
groups display.<o:p></o:p></span></p><p class=MsoNormal \
style='margin-left:36.0pt'><span lang=EN-GB><o:p> </o:p></span></p><p \
class=MsoNormal style='margin-left:36.0pt'><span lang=EN-GB>Typo : I just added \
‘over()’ after ST_ClusterDBSCAN<o:p></o:p></span></p><p \
class=MsoNormal style='margin-left:36.0pt'><span \
lang=EN-GB><o:p> </o:p></span></p><p class=MsoNormal \
style='margin-left:36.0pt'><span lang=EN-GB>Olivier<o:p></o:p></span></p><p \
class=MsoNormal style='margin-left:36.0pt'><span \
lang=EN-GB><o:p> </o:p></span></p><div><div style='border:none;border-top:solid \
#E1E1E1 1.0pt;padding:3.0pt 0cm 0cm 0cm'><p class=MsoNormal \
style='margin-left:36.0pt'><b>De :</b> postgis-users [<a \
href="mailto:postgis-users-bounces@lists.osgeo.org">mailto:postgis-users-bounces@lists.osgeo.org</a>] \
<b>De la part de</b> Regina Obe<br><b>Envoyé :</b> mercredi 2 août 2017 \
23:15<br><b>À :</b> 'PostGIS Users Discussion' <<a \
href="mailto:postgis-users@lists.osgeo.org">postgis-users@lists.osgeo.org</a>><br><b>Objet :</b> \
Re: [postgis-users] duplicated nodes<o:p></o:p></p></div></div><p class=MsoNormal \
style='margin-left:36.0pt'><o:p> </o:p></p><p class=MsoNormal \
style='margin-left:36.0pt'><span lang=EN-US style='color:#1F497D'>If you are running \
PostGIS 2.3 or above, I think ST_ClusterDBSCAN might do the trick for \
you:<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span \
lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal \
style='margin-left:36.0pt'><span lang=EN-US style='color:#1F497D'><a \
href="http://postgis.net/docs/manual-2.3/ST_ClusterDBSCAN.html">http://postgis.net/docs/manual-2.3/ST_ClusterDBSCAN.html</a><o:p></o:p></span></p><p \
class=MsoNormal style='margin-left:36.0pt'><span lang=EN-US \
style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal \
style='margin-left:36.0pt'><span lang=EN-US style='color:#1F497D'>You can set \
distance to 0 and minpoints to 2. All points that are not 0 distance from any \
other point will have NULL in the bucket column.<o:p></o:p></span></p><p \
class=MsoNormal style='margin-left:36.0pt'><span lang=EN-US style='color:#1F497D'>All \
other ones that have bucket numbers are duplicated.<o:p></o:p></span></p><p \
class=MsoNormal style='margin-left:36.0pt'><span lang=EN-US \
style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal \
style='margin-left:36.0pt'><span lang=EN-US \
style='color:#1F497D'>So:<o:p></o:p></span></p><p class=MsoNormal \
style='margin-left:36.0pt'><span lang=EN-US \
style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal \
style='margin-left:36.0pt'><span lang=EN-US style='color:#1F497D'>SELECT n.code, \
n.geom, ST_ClusterDBSCAN(n.geom, 0,2) AS bucket<o:p></o:p></span></p><p \
class=MsoNormal style='margin-left:36.0pt'><span lang=EN-US \
style='color:#1F497D'>FROM nodes <o:p></o:p></span></p><p class=MsoNormal \
style='margin-left:36.0pt'><span lang=EN-US \
style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal \
style='margin-left:36.0pt'><span lang=EN-US \
style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal \
style='margin-left:36.0pt'><span lang=EN-US style='color:#1F497D'>If you want the \
counts instead of the bucket, you can do<o:p></o:p></span></p><p class=MsoNormal \
style='margin-left:36.0pt'><span lang=EN-US \
style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal \
style='margin-left:36.0pt'><span lang=EN-US style='color:#1F497D'>SELECT o.code, \
o.geom, COUNT(*) OVER(PARTITION BY bucket) AS npoints, \
bucket<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span \
lang=EN-US style='color:#1F497D'>FROM (SELECT n.code, n.geom, \
ST_ClusterDBSCAN(n.geom, 0,2) AS bucket<o:p></o:p></span></p><p class=MsoNormal \
style='margin-left:36.0pt'><span lang=EN-US style='color:#1F497D'>FROM nodes ) \
AS o<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span \
lang=EN-US style='color:#1F497D'>WHERE bucket IS NOT NULL;<o:p></o:p></span></p><p \
class=MsoNormal style='margin-left:36.0pt'><span lang=EN-US \
style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal \
style='margin-left:36.0pt'><span lang=EN-US \
style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal \
style='margin-left:36.0pt'><span lang=EN-US style='color:#1F497D'>I didn't test so I \
might have a typo.<o:p></o:p></span></p><p class=MsoNormal \
style='margin-left:36.0pt'><span lang=EN-US \
style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal \
style='margin-left:36.0pt'><span lang=EN-US style='color:#1F497D'>Hope that \
helps,<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span \
lang=EN-US style='color:#1F497D'>Regina<o:p></o:p></span></p><p class=MsoNormal \
style='margin-left:36.0pt'><span lang=EN-US \
style='color:#1F497D'><o:p> </o:p></span></p><div><div \
style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0cm 0cm 0cm'><p \
class=MsoNormal style='margin-left:72.0pt'><b><span lang=EN-US>From:</span></b><span \
lang=EN-US> postgis-users [<a \
href="mailto:postgis-users-bounces@lists.osgeo.org">mailto:postgis-users-bounces@lists.osgeo.org</a>] \
<b>On Behalf Of </b>Olivier Leprêtre<br><b>Sent:</b> Wednesday, August 02, 2017 3:28 \
PM<br><b>To:</b> <a href="mailto:postgis-users@lists.osgeo.org">postgis-users@lists.osgeo.org</a><br><b>Subject:</b> \
[postgis-users] duplicated nodes<o:p></o:p></span></p></div></div><p class=MsoNormal \
style='margin-left:72.0pt'><span lang=EN-US><o:p> </o:p></span></p><p \
class=MsoNormal style='margin-left:72.0pt'>Hi,<o:p></o:p></p><p class=MsoNormal \
style='margin-left:72.0pt'><o:p> </o:p></p><p class=MsoNormal \
style='margin-left:72.0pt'><span lang=EN-GB>I have a point layer that contains \
several superposed nodes two, three times or more. I would like to display each group \
list and the number of item in each. I found this query which “works” but \
returns some false positive<o:p></o:p></span></p><p class=MsoNormal \
style='margin-left:72.0pt'><span lang=EN-GB><o:p> </o:p></span></p><p \
class=MsoNormal style='margin-left:72.0pt'><span lang=EN-GB>select case when \
lag(o.geom) OVER (PARTITION BY o.geom) = o.geom then '' else 'x ' || o.nbre::text \
end,d.code from<o:p></o:p></span></p><p class=MsoNormal \
style='margin-left:72.0pt'><span lang=EN-GB>(select geom,count(*) as nbre from nodes \
group by geom having count(*) >1) as o,<o:p></o:p></span></p><p class=MsoNormal \
style='margin-left:72.0pt'><span lang=EN-GB>lateral (select * from nodes) as d where \
st_within(o.geom,d.geom)<o:p></o:p></span></p><p class=MsoNormal \
style='margin-left:72.0pt'><span lang=EN-GB><o:p> </o:p></span></p><p \
class=MsoNormal style='margin-left:72.0pt'><span lang=EN-GB>I understand that false \
positives (yellow beneath) comes from “group by geom” which use a \
bounding box and catch close but not duplicated points.<o:p></o:p></span></p><p \
class=MsoNormal style='margin-left:72.0pt'><span \
lang=EN-GB><o:p> </o:p></span></p><p class=MsoNormal \
style='margin-left:72.0pt'><img border=0 width=90 height=191 \
style='width:.9416in;height:1.9916in' id="Image_x0020_1" \
src="cid:image001.jpg@01D30C78.0439C4E0" \
alt="cid:image001.jpg@01D30C78.0439C4E0"><span lang=EN-GB><o:p></o:p></span></p><p \
class=MsoNormal style='margin-left:72.0pt'><span \
lang=EN-GB><o:p> </o:p></span></p><p class=MsoNormal \
style='margin-left:72.0pt'><span lang=EN-GB>I tried other solutions which all get too \
complicated with several “join of join”. I would appreciate if someone \
has an idea on the top of his/her head !<o:p></o:p></span></p><p class=MsoNormal \
style='margin-left:72.0pt'><span lang=EN-GB><o:p> </o:p></span></p><p \
class=MsoNormal style='margin-left:72.0pt'><span \
lang=EN-GB>Thanks<o:p></o:p></span></p><p class=MsoNormal \
style='margin-left:72.0pt'><span lang=EN-GB><o:p> </o:p></span></p><p \
class=MsoNormal style='margin-left:72.0pt'><span \
lang=EN-GB>Olivier<o:p></o:p></span></p><p class=MsoNormal \
style='margin-left:72.0pt'><span \
lang=EN-GB><o:p> </o:p></span></p></div></body></html>
["image001.jpg" (image/jpeg)]
[Attachment #9 (text/plain)]
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