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?
asked Feb 22, 2015 at 19:46
DPSSpatial_BoycottingGISSEDPSSpatial_BoycottingGISSE
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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 WFeb 22, 2015 at 21:08
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1 Answer
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, 2015 at 19:54
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I'm struggling with visualizing this result - any thoughts? Is that what 'i' is? Feb 24, 2015 at 4:54
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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;Feb 24, 2015 at 6:41 -
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@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! Feb 24, 2015 at 17:12
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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] Feb 24, 2015 at 21:06