You don't need to build topology.
Have you tried something like:
select intersection(intersection (a.shape,b.shape),c.shape) , a.taxpin,
b.taxpin, c.taxpin
from tax.parcel a, tax.parcel b, tax.parcel c
where
a.taxpin != b.taxpin and
a.taxpin != b.taxpin and
st_dwithin(a.shape,b.shape,0) and
st_dwithin(c.shape,intersection (a.shape,b.shape),0)
;
In human terms
find the intersection of a tax parcel with the intersection of two
other parcels that share an edge (they have an intersection)
The intersection of an edge (line) and a no overlapping polygon would be
a point.
If your table has overlapping polygons this will return a slightly
different result.
You can order or group the results by
astext(intersection(intersection (a.shape,b.shape),c.shape))
To find nodes with more than three members.
C.
Andreas Neumann wrote:
Hello all,
I have a polygon mosaic (lets say administrative units, municipalities)
and would like to get a list of nodes where 3 or more polygons meet or 2
polygons depart at the edge of the mosaic. Is there any straight forward
way to extract these nodes?
I have read about topology support in Postgis and found this:
http://postgis.refractions.net/support/wiki/index.php?PostgisTopology -
whats the state of this project?
Thanks for any hints on my two questions.
Andreas
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