Hi Paul,
Yes, there is a way.
ST_PointN will extract the Nth point from a LINESTRING. When used with generate_series, you can extract all POINTs from
a LINESTRING.
(http://postgis.refractions.net/documentation/manual-svn/ST_PointN.html)
(http://www.postgresql.org/docs/8.3/static/functions-srf.html)
(http://postgis.refractions.net/documentation/manual-svn/ch07.html#Geometry_Accessors)
ST_GeometryN will extract the Nth geometry in a MULTILINESTRING. Again, use generate_series to extract all LINESTRINGs
from a MULTILINESTRING.
ST_Boundary will extract the boundary from a MULTIPOLYGON as a MULTILINESTRING.
So, put together, to extract all points from a table with MULTILINESTRINGs:
SELECT
ST_PointN(
lines,
generate_series(1, ST_NPoints(lines)))
FROM (
SELECT
ST_GeometryN(
ST_Boundary(the_geom),
generate_series(1, ST_NumGeometries(ST_Boundary(the_geom)))
) AS lines
FROM my_multipolygon_table
) AS foo;
You should note that there is no ST_Dump equivalent for points yet (ST_Dump expands MULTI* geometries extremely
quickly). Using generate_series is all we can do at the moment for extracting Points. If your geometries have more
than a few thousand points, you'll notice a significant reduction in performance. This is something we have on our TODO
list for future PostGIS enhancements.
On a side Paul, when creating a new topic, don't reply to an old thread or your question will get buried in someone
else's topic. Rather, create a new thread.
Hope that helps,
Kevin
Moen, Paul T. wrote:
Is there an easy way to get all the points from a geometry? For
instance, I have a multipolygon and I would like to get the distance
from a point to each point that makes up the multipolygon. I know how
to do it by parsing the wkt, but was wondering if there was a better way
to do it using Postgis and SQL.
Thanks,
Paul
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