[postgis-users] Nearest point on line

[Martin Davis]

Have a look at JTS - it has code to do this (in the DistanceOp class).
 
http://www.vividsolutions.com/jts/jtshome.htm
 
 
 
Martin Davis, Senior Technical Architect
Vivid Solutions Inc.      www.vividsolutions.com
Suite #1A-2328 Government Street Victoria, B.C. V8T 5G5
Phone: (250) 385 6040 - Local 308 Fax: (250) 385 6046

	-----Original Message-----
	From: Derek C. Figg [mailto:derek at cxtsoftware.com] 
	Sent: April 11, 2005 1:39 PM
	To: postgis-users at postgis.refractions.net
	Subject: [postgis-users] Nearest point on line
	
	
	Hello all,
	 
	Please excuse this question if it is very basic or has been
answered recently.  I have searched online for hours to no avail looking
for an answer.
	 
	I have a database full of linestrings (StreetLine).  I am
searching this database to find the line string that is closest to a
specified point.  I am successfully able to do this with this code:
	 
	CREATE FUNCTION rg (decimal (9,6), decimal (9,6)) RETURNS SET OF
tblImportData AS $$
	SELECT *
	 FROM tblImportData
	 WHERE "StreetLine" && Expand(GeomFromText('POINT(' || $1 || ' '
|| $2 || ')',-1),.0004)
	  AND Distance(GeomFromText('POINT(' || $1 || ' ' || $2 ||
')',-1),"StreetLine") < .0004
	 ORDER BY Distance(GeomFromText('POINT(' || $1 || ' ' || $2 ||
')',-1),"StreetLine")
	 LIMIT 1;
	$$ LANGUAGE SQL;
	
	I want to go a step further though, and determine what exact
point on the linestring is closest to the point I have specified.
Basically, I want to know the intersecting point on the linestring where
the distance from the specified point to the line is smallest.  Thanks
in advance for any info that you can provide me.
	 
	Derek Figg
	 

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