[postgis-users] Length of a line above polygon

[Denis Rouzaud]

Yes, you're right.

This should solve this problem:

SELECT areas.id, SUM( ST_Length( ST_Intersection( lines.geometry , 
areas.geometry ) ) )
FROM lines,areas
GROUP BY areas.id ;

ST_intersects returns true if there is an intersection and 
ST_Intersection returns the share geometry.

Greetings,

Denis



On 07/04/2012 08:47 AM, Matej Mailing wrote:
> Hi,
>
> Thank you for the answer. However, I don't get the right result. For
> example, when there is a line that is long 500 meters and it crosses 5
> polygons (on each of them maybe just a meter or few meters, except one
> where lies a majority of the line), I get the full length of the lines
> for corresponding polygons - i.e. as every polygon that is crossed is
> crossed by the total line length. What I want to get is the actual
> length of the part of the line that crosses every specific polygon.
>
> TIA,
> Matej
>
>
> 2012/7/3 Denis Rouzaud <denis.rouzaud at gmail.com>:
>> Hi,
>>
>> You can use something like
>>
>> SELECT areas.id, SUM( ST_Length( lines.geometry) ) FROM lines,areas WHERE
>> ST_Intersects(lines.geometry,areas.geometry) GROUP BY areas.id ;
>>
>> Greetings,
>>
>> Denis
>>
>>
>> On 07/03/2012 01:36 PM, Matej Mailing wrote:
>>> Hi all,
>>>
>>> We have a layer that contains polygons and another that contains lines
>>> that lie on them. Parts of the lines are laying "inside" the polygons
>>> and I would like to get a sum of all the lengths of lines that lie on
>>> the polygons. What is the easiest way to achieve this?
>>>
>>> TIA,
>>> Matej
>>> _______________________________________________
>>> postgis-users mailing list
>>> postgis-users at postgis.refractions.net
>>> http://postgis.refractions.net/mailman/listinfo/postgis-users
>>
>>