[GIS] Merge polygons in postgis

postgisunion

I have a hand-digitized coverage stored in postgis. There, I have a few shiver-polygons I would like to get rid of by including them into one of the neighbouring polygons.

are there any commands that can be used to do that?

Something like

update coverage set the_geom=st_union(…) …

Of cource, I want to use the attributes from the large polygon – I must be able t decide which way the union goes.

Best Answer

SQL:

UPDATE coverage SET the_geom = ST_Union(
(SELECT the_geom FROM coverage WHERE id = :polygon_id),
(SELECT the_geom FROM coverage WHERE id = :sliver_id)
)
WHERE id = :polygon_id;

Is that what You meant?

Related Solutions

PostGIS Topology – Dealing with Ring Self-Intersections

I think what is happening is that your self-intersecting polygons becomes MULTIPOLYGONS when buffering.

you have two options:

1 remove the constraint "enforce_geotype_the_geom", you can do that in pgAdmin
2 put the result in a new table instead of updating the old. that is often a good way of doing things because then you don't change anything in your original table. the query can look something like:

CREATE TABLE new_buffered_table as
SELECT ST_Buffer(the_geom,0.0) as the_geom, gid FROM original_table;

of course you might want to bring more fields to your new table.

try the buffer trick first. In the second approach Paul can tell himself what affect the empty linestring has. I don't remember how that magic happens.

[GIS] PostGIS Dissolve/Union close polygons

I think you should use ST_Dump to disaggregate your Multi-part polygon created in your step (1):

SELECT ST_Dump( 
   ST_Union(ST_SnapToGrid(the_geom,0.0001))
   FROM parishes
   GROUP BY county_name
);

Best Answer

Related Solutions

PostGIS Topology – Dealing with Ring Self-Intersections

[GIS] PostGIS Dissolve/Union close polygons

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