What's the PostGIS equivalent to Extract Nodes in fTools / QGIS? [duplicate]

Question

This question already has an answer here:

I'm looking to convert Park polygons from OSM into points.

The QGIS fTools Extract Nodes tool will convert a polygon to points at the vertices.

What is the equivalent function or work-flow in PostGIS?

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I will confess that the other question goes a step further to get coordinates, and not just using st_dump to get the points, so my flag of duplicate may have been a bit hasty. I apologize if you consider this to be significantly different to not warrant marking as a duplicate. — Chris W, Feb 22 '15 at 21:08

Nicklas Avén · Accepted Answer · 2015-02-24 06:50:50Z

4

Yo can use ST_DumpPoints(geom) to get the points listed.

Look at the example how to use it.

The result contains both the geometry and a path telling where in the polygon the point belongs. So to just get the geometry (points) do like this:

SELECT (ST_DumpPoints(the_geom)).geom

answered Feb 22 '15 at 19:54

Nicklas Avén

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I'm struggling with visualizing this result - any thoughts? Is that what 'i' is? – DPSSpatial Feb 24 '15 at 4:54
mapBaker -- what are you using for visualizing. Not sure what Nicklas meant by i. There is a path property which is an array of integers defining depth in geometry. You should be able to visualize this in QGIS DbManager with - SELECT (g).path[1], (g).geom FROM (SELECT ST_DumpPoints(geom) As g FROM sometable) As f; – LR1234567 Feb 24 '15 at 6:41
Just a typo. It should have been "it" :-) – Nicklas Avén Feb 24 '15 at 6:51
@LR1234567 I can only get PATH values of '1' for that query. I am getting back the correct number of nodes, so for now, I'll say I need to work on my workflow for how to use these points... Thank you both! – DPSSpatial Feb 24 '15 at 17:12
If you have polygons/multipolygs path[1] is the index of the polygon the point belongs to. Not interesting unless you have a multipolygon. path[2] would be the ring . path[3] would be the index position of the point in the ring. So I'm guessing maybe what you want is path[3] – LR1234567 Feb 24 '15 at 21:06

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marked as duplicate by Chris W, PolyGeo♦ Feb 22 '15 at 21:04