'Re: [postgis-users] Round up coordinates?'

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List:       postgis-users
Subject:    Re: [postgis-users] Round up coordinates?
From:       Nicklas_Avén <nicklas.aven () jordogskog ! no>
Date:       2010-06-24 7:19:36
Message-ID: 201006240719.o5O7JasJ002893 () mail-core ! space2u ! com
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Hallo

The problem is that even if you round your coordinates with ST_SnapToGrid, the edges \
between the vertexes will cross "not rounded land". So the intersection will most \
likely fail without the buffer if the intersection is expected somewhere between the \
rounded vertex points.

Another way of doing it is using ST_DWithin instead. I don't know which one is most \
effective.

Hope That Helps
Nicklas

2010-06-23 João Paulo Hespanha  wrote:

I have a number of cadastral boundaries (in predio_polylines) and
> property beacons (in propertybeacon) in a PostGIS database. The
> coordinates have a non-default srid of 9102160 and are stored with
> double precision. 
> When I run the following topological query (boundaries crossing a
> certain beacon) without the buffer, I get no results. The data has an
> internal resolution of 0.01 meter (from original source) and quality no
> better than 0.1 meter. How can I round up the coordinates such that the
> query can run without the buffer?
> 
> BTW, is it possible to build a small graphical form to run the querying,
> changing the b.gid parameter? (in uDIG? :-)
> 
> 
> Topo query:
> select
> 	l.gid,
> 	l.nfolhapred,
> 	b.gid,
> 	b.tipo
> from
> 	predio_polylines as l,
> 	propertybeacon as b
> where
> 	b.gid = 1000 AND
> 	(ST_Intersects(ST_Buffer(ST_EndPoint(l.the_geom), 0.01),
> ST_Buffer(b.the_geom, 0.01)) OR
> 	ST_Intersects(ST_Buffer(ST_StartPoint(l.the_geom), 0.01),
> ST_Buffer(b.the_geom, 0.01)));
> 
> 
> _______________________________________________
> postgis-users mailing list
> postgis-users@postgis.refractions.net
> http://postgis.refractions.net/mailman/listinfo/postgis-users
> 
> 

[Attachment #5 (unknown)]

<html>
<head>
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<body>Hallo<br />
	<br />
	The problem is that even if you round your coordinates with ST_SnapToGrid, the edges \
between the vertexes will cross "not rounded land". So the intersection will most \
likely fail without the buffer if the intersection is expected somewhere between the \
rounded vertex points.<br />  <br />
	Another way of doing it is using ST_DWithin instead. I don't know which one is most \
effective.<br />  <br />
	Hope That Helps<br />
	Nicklas<br />
	<br />
	<br />
	 2010-06-23 João Paulo Hespanha  wrote:<br />
	<br />
	I have a number of cadastral boundaries (in predio_polylines) and<br />

> property beacons (in propertybeacon) in a PostGIS database. The<br />

> coordinates have a non-default srid of 9102160 and are stored with<br />

> double precision. <br />

> When I run the following topological query (boundaries crossing a<br />

> certain beacon) without the buffer, I get no results. The data has an<br />

> internal resolution of 0.01 meter (from original source) and quality no<br />

> better than 0.1 meter. How can I round up the coordinates such that the<br />

> query can run without the buffer?<br />

> <br />

> BTW, is it possible to build a small graphical form to run the querying,<br />

> changing the b.gid parameter? (in uDIG? :-)<br />

> <br />

> <br />

> Topo query:<br />

> select<br />

> 	l.gid,<br />

> 	l.nfolhapred,<br />

> 	b.gid,<br />

> 	b.tipo<br />

> from<br />

> 	predio_polylines as l,<br />

> 	propertybeacon as b<br />

> where<br />

> 	b.gid = 1000 AND<br />

> 	(ST_Intersects(ST_Buffer(ST_EndPoint(l.the_geom), 0.01),<br />

> ST_Buffer(b.the_geom, 0.01)) OR<br />

> 	ST_Intersects(ST_Buffer(ST_StartPoint(l.the_geom), 0.01),<br />

> ST_Buffer(b.the_geom, 0.01)));<br />

> <br />

> <br />

> _______________________________________________<br />

> postgis-users mailing list<br />

> postgis-users@postgis.refractions.net<br />

> http://postgis.refractions.net/mailman/listinfo/postgis-users<br />

> <br />

> 

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