[postgis-users] Length of a line above polygon

[Denis Rouzaud]

Messages crossed, but seems we agree ;)



On 07/04/2012 08:51 AM, Matej Mailing wrote:
> I think I have just found it out. I just add ST_Intersection to have a
> query like:
> SELECT areas.id, SUM( ST_Length( ST_Intersection(lines.geometry,
> areas.geometry) ) ) FROM lines,areas WHERE
> ST_Intersects(lines.geometry,areas.geometry) GROUP BY areas.id ;
>
> Now the numbers seem to be correct :-) Hopefully this could be of some
> use to anyone else when having such a problem.
>
> Thanks,
> Matej
>
>
> 2012/7/4 Matej Mailing <mailing at tam.si>:
>> 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
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>>>
>>>