I dont't have any experience with geographics databases so I hope that you be patiente with me, so I opened this question (PostGis and datatypes WKT) in the past week about the datatypes in the postgis, but later I continued to read the documentation and then I found the following.
- ST_Curve = http://postgis.net/docs/manual-2.3/ST_Length.html
- ST_Geometry = http://postgis.net/docs/manual-2.3/ST_GeomFromEWKB.html
- ST_Surface = http://postgis.net/docs/manual-2.3/ST_Area.html
What are these datatypes? they are instanciable? and why they aren't here https://github.com/postgis/postgis/blob/svn-trunk/liblwgeom/liblwgeom.h.in#L82 (that link is the link that was used to answer my question that I mencioned on the begining of the question)