GEOSConcaveHull returns null with MultiPolygon

[Shijie li]

I want to try using the GeosConcaveHull function to calculate the concave hull of a polygon, so I have the following query:

WITH mp AS(

SELECT ST_GeomFromText('MULTIPOLYGON (((0 0, 1 0, 2 1, 1 1, 0 0)),
                      ((8 2, 8 4, 10 4, 10 2, 8 2)),
                      ((4 9, 5 9, 5 8, 4 8, 4 9)))'
) geom
)

SELECT GeosConcaveHull(mp.geom, 1,TRUE) from mp;

But it returned NULL, so I used the ST_SsValid function to check if the polygon was valid, and it returned -1.

This MultiPolygon should be valid.

[a.fu...@lqt.it]

I'm sorry,

but once again I cannot confirm your claim.
testing on my own PC:

WITH mp AS(
SELECT ST_GeomFromText('MULTIPOLYGON (((0 0, 1 0, 2 1, 1 1, 0 0)),
((8 2, 8 4, 10 4, 10 2, 8 2)),
((4 9, 5 9, 5 8, 4 8, 4 9)))'
) geom
)

SELECT ST_AsText(GeosConcaveHull(mp.geom, 1,TRUE)) from mp;
------------------
POLYGON((4 9, 5 9, 10 4, 10 2, 1 0, 0 0, 4 9))


and then testing ST_IsValid() on the input MultiPolygon
returns 1 (not -1, that usually means INVALID ARG)

bye Sandro

[Shijie li]

Sorry, I ran this query correctly on spatialite. The incorrect result was caused by my improper operation in QGIS.