[postgis-users] Dividing an area to closest line

[Obe, Regina]

Why wouldn't you use a nearest neighbor calculation as demonstrated here (using DISTINCT ON)?
 
http://postgis.refractions.net/documentation/manual-svn/ST_DWithin.html
 
Keep in mind ST_DWithin and  ST_Distance don't care about whether a geometry is a line or polygon or point or collection or whatever.  They will always consider the minimum distance between 2 geometries.
 
ST_DWithin will use a spatial index where as ST_Distance will not.  So for ST_DWithin to work, you have to make the assumption,
the closest road to any point is no more than X units away.  The bigger you make the X, the less efficient the index search, but the less likely you will leave a point out.
 
Hope that helps,
Regina

________________________________

From: postgis-users-bounces at postgis.refractions.net [mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of nicklas.aven at jordogskog.no
Sent: Monday, December 29, 2008 3:18 AM
To: postgis-users at postgis.refractions.net
Subject: [postgis-users] Dividing an area to closest line


Hallo
 
My first time writing here.
 
The case is that I need to find the closest road from every point in the terrain. The roads are defined in "roadparts". The very best thing would be to get polygons around every roadpart which I could use on other data to bind it to the right road.
 
The only solution I can see is making a raster of small rektangels that I bind to my roadparts using nearest neighbour-calculations.
 
My question is if someone has a more efficient and better solution.
 
Sorry for my bad english
 
Thanks
/Nicklas Avén


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