Bug in documentation for ST_StraightSkeleton and ST_ApproximateMedialAxis

[br0ke]

It is said in docs that ST_StraightSkeleton and ST_ApproximateMedialAxis are working with 3D geometries and don't drop z-index, but in fact they always return 2d geometry whether I pass 2d or 3d input geometry.

Is it a bug in documentation?

SELECT ST_AsText(ST_ApproximateMedialAxis(ST_GeomFromText('POLYGON((0 0 10, 0 50 10, 10 50 10, 10 0 10, 0 0 10))')))

+-----------------------------+
| st_astext                   |
|-----------------------------|
| MULTILINESTRING((5 5,5 45)) |
+-----------------------------+


SELECT ST_AsText(ST_ApproximateMedialAxis(ST_GeomFromText('POLYGON Z ((0 0 10, 0 50 10, 10 50 10, 10 0 10, 0 0 10))')))

+-----------------------------+
| st_astext                   |
|-----------------------------|
| MULTILINESTRING((5 5,5 45)) |
+-----------------------------+


SELECT ST_AsEWKT(ST_ApproximateMedialAxis(GeomFromEWKT('POLYGON((0 0 10, 0 50 10, 10 50 10, 10 0 10, 0 0 10))')))

+-----------------------------+
| st_asewkt                   |
|-----------------------------|
| MULTILINESTRING((5 5,5 45)) |
+-----------------------------+


SELECT ST_AsEWKT(ST_ApproximateMedialAxis(GeomFromEWKT('POLYGON Z((0 0 10, 0 50 10, 10 50 10, 10 0 10, 0 0 10))')))

+-----------------------------+
| st_asewkt                   |
|-----------------------------|
| MULTILINESTRING((5 5,5 45)) |
+-----------------------------+

PostGIS version: POSTGIS="2.3.7 r16523" PGSQL="95" GEOS="3.4.2-CAPI-1.8.2 r3921" SFCGAL="1.3.0" PROJ="Rel. 4.8.0, 6 March 2012" GDAL="GDAL 1.10.1, released 2013/08/26" LIBXML="2.9.1" LIBJSON="0.11.99" RASTER

PostgreSQL version: PostgreSQL 9.5.11 on x86_64-pc-linux-gnu (Debian 9.5.11-1.pgdg80+1), compiled by gcc (Debian 4.9.2-10) 4.9.2, 64-bit

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