Hi Sandro,
I guess you been something like this:
select
st_difference(
st_buffer(st_pointfromtext('POINT(680386.8879388
5152170.83093339)',82344),9000.0),
st_union(
st_buffer(st_pointfromtext('POINT(688402.843016069
5157054.21005474)',82344),3000.0),
st_union(
st_buffer(st_pointfromtext('POINT(680910.532411225
5142908.46168964)',82344),5000.0),
st_buffer(st_pointfromtext('POINT(674802.141078014
5161560.18713918)',82344),5860.0)
)
)
)
cheers Markus
--
Ph D. Student Markus Innerebner
DIS Research Group - Faculty of Computer Science
Free University Bozen-Bolzano
Dominikanerplatz 3 - Room 211
I - 39100 Bozen
Phone: +39-0471-016143
Mobile: +39-333-9392929
gpg --fingerprint
-------------------------------------
pub 1024D/588F6308 2007-01-09
Key fingerprint = 6948 947E CBD2 89FD E773 E863 914F EB1B 588F 6308
sub 2048g/BF4877D0 2007-01-09
On Sep 11, 2012, at 5:26 PM, Sandro Santilli wrote:
> On Tue, Sep 11, 2012 at 04:29:07PM +0200, Markus Innerebner wrote:
>> Hello,
>>
>> I have a question regarding the st_difference operation:
>>
>> I want to identify the non overlapping area of a given polygon, that might
>> intersect with arbitrary other polygons.
>> I realized, that st_difference operation works only with two parameters. The
>> API says not to use it with geometry collections.
>>
>> In order to realize this, I needed to do combine st_intersection with
>> st_difference in recursive manner as shown below with the following output:
>>
>>
>> st_intersection(
>> st_intersection(
>> st_difference(
>> st_buffer(st_pointfromtext('POINT(680386.8879388
>> 5152170.83093339),82344),9000.0),
>> st_buffer(st_pointfromtext('POINT(688402.843016069
>> 5157054.21005474),82344),3000.0)
>> ),
>> st_difference(
>> st_buffer(st_pointfromtext('POINT(680386.8879388
>> 5152170.83093339),82344),9000.0),
>> st_buffer(st_pointfromtext('POINT(674802.141078014
>> 5161560.18713918),82344),5860.0)
>> )
>> ),st_difference(
>> st_buffer(st_pointfromtext('POINT(680386.8879388
>> 5152170.83093339),82344),9000.0),
>> st_buffer(st_pointfromtext('POINT(680910.532411225
>> 5142908.46168964),82344),5000.0)
>> )
>> )
>> )
>> )
>>
>> my question now is: Is there a simpler way?
>
> You may union the parts to subtract and then call difference only once.
> Leaving out the parts that do not intersect with the bounding box of
> the first geometry is advisable.
>
> --strk;
>
> http://www.cartodb.com - Map, analyze and build applications with your data
>
> ~~ http://strk.keybit.net
>
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