[OSGeo Africa] Question on PostGIS

[Charles Rethman]

Hi Glen,

Thank you so much for this, it's really helpful! I'm trying it out now with my data.

All the best, Charles.

> On 14 Mar 2014, at 5:54 PM, Glenn Mullett <GMullett at lidwala.com> wrote:
> 
> Hi Charles
> 
> To explode geomteries, you can use st_dump
> 
> e.g.
> 
> select
>     gid,
>     st_geometrytype(the_geom) as orig_geom_type, 
>     st_nrings(the_geom) as orig_geom_number_rings,
>     st_geometrytype((st_dump(the_geom)).geom) as dumped_geom_type,
>     (st_dump(the_geom)).path as dumped_geom_ordinal_num,
>     (st_dump(the_geom)).geom as dumped_geom,
>     main_place
> from static_main_place 
> order by 1,5
> 
> (see my pic below with some comments and the result...)
> 
> <st_dump.png>
> 
> 
> 
> 
> 
> 
> Kind regards,
> Glenn Mullett
> H.O.D. GIS [MSc GIS, Btech Nat. Cons.]
> Lidwala Consulting Engineers
> 
> <lidwala.jpg>P.O. Box 2930, Nelspruit, 1200
> Tel: 0861 LIDWALA / 0861 543 9252
> Fax: 086 766 2829
> Cell: 082 922 3831
> Website: www.lidwala.com
> Mailto: gmullett at lidwala.com
> <thinkbeforeprint.jpg>
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>> On 14/03/14 17:04, Charles Rethman wrote:
>> Hello PostGIS experts out there, I have a technical question for you all...
>> 
>> I need to effect 'clips' in PostGIS and I have tried using ST_Difference. I got very messy outputs and then I read in the PostGis Manual the the function doesn't work with Collections. In importing my shape file data into PostGIS, I created multi-polygon geometries--so I presume that is why the ST_Difference function won't give me sensible results.
>> 
>> Is there a function or a way in PostGIS of converting multi-polygons into single polygons (a kind of 'explode' function) so that I don't have to re-import all my shape files (I really HATE those old shape files!)
>> 
>> I am using PostGIS 2.1 on postgres 9.3...
>> 
>> Thank you for your time,
>> 
>> Charles Rethman
>> Director, Cape Town Office
>> 
>> Cell: +27 71 6735502
>> Tel: +27 21 6861510
>> Skype: cwrethman
>> PO Box 23507, Claremont, 7735, South Africa
>> 19 Sans Souci Road, Newlands, 7700, Cape Town
>> 
>> 
>> 
> 
> <st_dump.png>
> <lidwala.jpg>
> <thinkbeforeprint.jpg>
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