[OSGeo Africa] Question on PostGIS

[Glenn Mullett]

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_example]






Kind regards,
Glenn Mullett
H.O.D. GIS [MSc GIS, Btech Nat. Cons.]
Lidwala Consulting Engineers

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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


[X]<http://www.wahenga.co.za>

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