I have a LineString geometry which is U shaped like and I'd like to find the center point of the geometry which lies on the LineString. I've already used st_centroid but the returned geometry isn't on the LineString.
I would like to know which function should be used in PostGIS to achieve that?
The documentation for st_centroid, st_pointOnSurface and st_line_interpolate_point have neat images describing them.
st_centroid gives you the geometric centroid point, which can be outside of the source geometry (think of a line shaped as a U, the centroid will not be on the line).
st_pointOnSurface returns a point that is for sure on the surface (on the line, inside a polygon), but you don't know where it is. It is very useful for label placement.
st_line_interpolate_point, used with a parameter of .5 (50%) will return the point, on the input line, located in the middle.
