[postgis-users] ST_Difference

[Richard Heimann [C]]

Thanks Paul for the response. I hadn’t thought of this logic, it didn’t work
however. Strangely, it increased the number of features by eight times. Any
thoughts? 

Vr
Rich
 


-----Original Message-----
From: Paul Ramsey [mailto:pramsey at refractions.net] 
Sent: Wednesday, October 24, 2007 4:07 PM
To: Richard.Heimann at nrl.navy.mil; PostGIS Users Discussion
Subject: Re: [postgis-users] ST_Difference

select p.*
from pandatestdata p, world2_12nm w
where not st_contains(w.the_geom, p.the_geom);

On 24-Oct-07, at 11:45 AM, Richard Heimann [C] wrote:

> Thanks for your response W. I should have posted the sql query  
> earlier.
> Anyway...its below.
>
> My goal is to drop all features (points) that fall within my  
> polygon. In
> this case, I have ship track data and want to filter it with world  
> country
> buffers.
>
> World2_12nm - my world country 12nm buffered polygon
> Pandatestdata - track data (point)
> Panda_diff2 - new table
>
>
> CREATE TABLE panda_diff2 AS
> SELECT AsText(Difference(world2_12nm.the_geom,  
> pandatestdata.the_geom)) FROM
> world2_12nm, pandatestdata
>
> Also attached are the astext versions of my data as well as a csv  
> of the
> output from the above sql. Please debunk the mystery...
>
> Thanks again
> Rich
>
> -----Original Message-----
> From: Webb Sprague [mailto:webb.sprague at gmail.com]
> Sent: Wednesday, October 24, 2007 12:00 PM
> To: Richard.Heimann at nrl.navy.mil; PostGIS Users Discussion
> Subject: Re: [postgis-users] ST_Difference
>
> You might get more useful help if you post an "astext()" version of
> your data, the query, the result, and  a *desired* result.
>
> I know the difference functions can be tricky and are sometiimes
> defined in ways you might not expect.
>
> Thx
> W
>
> On 10/24/07, Richard Heimann [C] <heimann at ait.nrl.navy.mil> wrote:
>>
>>
>>
>>
>> All,
>>
>>
>>
>> I would appreciate help in constructing an SQL statement that  
>> performs a
>> difference function on two datasets. My intersect function works but
> cannot
>> work out the kinks with st_difference. Thanks for your help.Im new to
>> Postgis.
>>
>>
>>
>> Rich
>>
>>
>>
>>
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>>
>
>
>
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