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How can I get the length (brown marked part) of the "Road 7" inside the red polygon?

a busy cat

My start:

SELECT ST_Length(way) FROM lines WHERE road = "Road 7" AND ST_Intersects(line, polygon)?

With that, I get only the total length :( Someone has an idea?

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up vote 11 down vote accepted

It's necessary to calculate the actual intersection, e.g. http://postgis.net/docs/ST_Intersection.html

SELECT ST_Length(ST_Intersection(line,polygon)) 
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You beat me to it. +1 this should do it. – GIS-Jonathan Jun 12 '12 at 11:26

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