[postgis-users] creating a mask

[erik]

Thanks Regina & Fred.

That did the trick all right!

Regards

On Thu, Aug 7, 2008 at 3:46 PM, Fred Lehodey <lehodey at gmail.com> wrote:

> Hi Erik,
> you can try something like that:  (?)
> select  st_difference(ST_envelope(the_geom),the_geom)  from mytable
>
> Fred
>
>
>
> On Thu, Aug 7, 2008 at 2:11 PM, erik <whatevar89 at gmail.com> wrote:
>
>> Hello,
>>
>> I don't know if the terminology I use is correct but I would like to
>> create a mask of layer I have.
>> For example, from the shape of the world I would like to keep only the
>> oceans, the negative of the initial shape.
>> I haven't found any info or documentation about this. Can this be done in
>> PostGIS?
>>
>> Many thanks!
>>
>> Erik
>>
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>>
>>
>
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