ST_NDims — Returns coordinate dimension of the geometry as a small int. Values are: 2,3 or 4.
integer ST_NDims(
geometry g1)
;
Returns the coordinate dimension of the geometry. PostGIS supports 2 - (x,y) , 3 - (x,y,z) or 2D with measure - x,y,m, and 4 - 3D with measure space x,y,z,m
This function supports 3d and will not drop the z-index.