<html><head><style type="text/css"><!-- DIV {margin:0px;} --></style></head><body><div style="font-family:arial, helvetica, sans-serif;font-size:12pt"><DIV>Simon,</DIV>
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<DIV>Thanks for the SQL, I will first figure it out and then exercise it on my dataset. It seems that to be able to use previous SQLs, I needed to merge/clean first my linestring in order to get exactly two rows for each river. By the way, river mouth means the start point of the river banks. </DIV>
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<DIV>kind regards,</DIV>
<DIV><BR>surya</DIV>
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<B><SPAN style="FONT-WEIGHT: bold">From:</SPAN></B> Simon Greener <simon@spatialdbadvisor.com><BR><B><SPAN style="FONT-WEIGHT: bold">To:</SPAN></B> PostGIS Users Discussion <postgis-users@postgis.refractions.net><BR><B><SPAN style="FONT-WEIGHT: bold">Sent:</SPAN></B> Mon, October 19, 2009 10:17:34 AM<BR><B><SPAN style="FONT-WEIGHT: bold">Subject:</SPAN></B> Re: [postgis-users] Help determining position<BR></FONT><BR>Surya,<BR><BR>> with help of the list I am able to determine minimum width of a river using SQL below. Especially thanks to Mr. Simon Greener.. I still need to determine position (in meter and also latlon) of this point from the river mounth. Can anybody give me suggestion what Postgis function I should use together with the following SQL.<BR><BR>Not going to do everything for you (after all you have not supplied us a definition of the river mouth), but I would probably start by trying to find the actual points in the
left/right bank that are closest via something like this:<BR><BR><BR>-- Which points are closest to each other?<BR>--<BR>SELECT l.rin,ST_Point((l.coord).x,(l.coord).y),<BR> r.rin,ST_Point((r.coord).x,(r.coord).y),<BR> ST_Distance(ST_Point((l.coord).x,(l.coord).y),<BR> ST_Point((r.coord).x,(r.coord).y)) as PDistance<BR> FROM (select row_number() over (order by the_geom) as rin,<BR> ST_DumpPoints(the_geom) as coord<BR> from River r<BR> where r.Name = 'Barito' ) as l,<BR> (select row_number() over (order by the_geom) as rin,<BR> ST_DumpPoints(the_geom) as coord<BR> from River r<BR> where r.Name = 'Barito' ) as
r<BR>WHERE l.rin <> r.rin<BR>ORDER BY 5 ASC<BR>LIMIT 1;<BR><BR>Note, the ST_DumpPoints() function is a user defined one you can get from http://www.spatialdbadvisor.com/postgis_tips_tricks/109/implementing-oracles-getvertices-function-in-postgis-st_dumppoints<BR><BR>But this will return the left and right points that are closest. Then you need to calculate the distance from each point to the point that defines the mouth of your river and chose the closest.<BR><BR>regards<BR>Simon<BR><BR>--SpatialDB Advice and Design, Solutions Architecture and Programming,<BR>Oracle Database 10g Administrator Certified Associate; Oracle Database 10g SQL Certified Professional<BR>Oracle Spatial, SQL Server, PostGIS, MySQL, ArcSDE, Manifold GIS, FME, Radius Topology and Studio Specialist.<BR>39 Cliff View Drive, Allens Rivulet, 7150, Tasmania, Australia.<BR>Website: <A href="http://www.spatialdbadvisor.com/" target=_blank>www.spatialdbadvisor.com</A><BR>
Email: <A href="mailto:simon@spatialdbadvisor.com" ymailto="mailto:simon@spatialdbadvisor.com">simon@spatialdbadvisor.com</A><BR> Voice: +61 362 396397<BR>Mobile: +61 418 396391<BR>Skype: sggreener<BR>Longitude: 147.20515 (147° 12' 18" E)<BR>Latitude: -43.01530 (43° 00' 55" S)<BR>GeoHash: r22em9r98wg<BR>NAC:W80CK 7SWP3<BR>_______________________________________________<BR>postgis-users mailing list<BR><A href="mailto:postgis-users@postgis.refractions.net" ymailto="mailto:postgis-users@postgis.refractions.net">postgis-users@postgis.refractions.net</A><BR>http://postgis.refractions.net/mailman/listinfo/postgis-users<BR></DIV></DIV></div><br>
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