Returns the transform definition of the spatial reference system that is the source of the projection.
SELECT ST_SpatialRefSys::ST_GetUnProjectedTransformDefinition( '+proj=robin +lon_0=0 +x_0=0 +y_0=0 +a=6371000 +b=6371000 +units=m no_defs' )
SQL/MM (ISO/IEC 13249-3: 2006) Vendor extension