prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#>
prefix geo: <http://www.opengis.net/ont/geosparql#>
prefix geof: <http://www.opengis.net/def/function/geosparql/>

select distinct (geof:envelope(?xGeom) as ?s)
where {
	?x geo:asWKT ?xGeom.
}