[postgis-users] Question about Crosses(geometry, geometry)

[Matt Doughty]

Hi List,

 

I've a question about the CROSSES (geometry, geometry) function. I'd
like to use it to select lines from a table that do not cross, or
intersect, some polygons in a separate table. 

 

The following script lets me select the lines that cross the polygons:

 

SELECT 

            lines.*

FROM 

            lines, 

            polygons

WHERE 

            CROSSES(lines.the_geom, polygons.the_geom)

 

Now I'd like to place a 'NOT' before the function CROSSES (-> NOT
CROSSES(lines.the_geom, polygons.the_geom), rather naively it seems, as
doing that returns me a table with the same geometry as the original
layer, but with 30 times more rows (an increase of 400 to 12,000
records). In other words, it hasn't 'selected' and lines out of the
layer, merely repeated the table geometry 30 times.

 

Can anybody explain where I'm going wrong?

 

Many thanks in advance,

 

Matt

 

 

 

Matt Doughty

 

GEOGRAMA S.L.

Tel.:  +34 945 13 13 72    652 77 14 15

Fax: +34 945 23 03 40 

www.geograma.com <http://www.geograma.com/> 

 

 

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