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I am trying to find out how to get the bounding box of several geometries in teradata. I am currently working with 13.00 and have tried the following:

select SYSSPATIAL.AggGeomUnion(cast(geom.ST_Envelope() as VARBYTE(64000))) from road;
select SYSSPATIAL.AggGeomUnion(geom.ST_Envelope()) from road;

both of these statements return a byte array which is not wkb. The docs says it is a varbyte and can be cast to an ST_Geometry which I tried with the following statment:

select cast(SYSSPATIAL.AggGeomUnion(cast(geom.ST_Envelope() as VARBYTE(64000))) as ST_GEOMETRY) from road;