LlGetRegionCorner

Returns a vector in meters that is the global location of the south-west corner of the region the object is in. The z component is 0.0

//calculates your position relative to <0,0,0> of 'Da Boom' in meters when you touch it
vector vecrel; //a sum of llgetpos and llgetregioncorner (and another vector). Saving time doing vector math.
 
default
{
    state_entry()
    {
        llSetText("Touch me to get your position", <1,1,1>, 2.0);
    }
    touch_start(integer total_number)
    {
        vecrel = llGetRegionCorner() + llDetectedPos(0);
        llWhisper(0, "llGetRegionCorner() is:"+(string)vecrel ); //for debugging before vector addition
        vecrel -= <256000.0, 256000.0, 0.0>;//Da Boom's region corner is at <256000.0, 256000.0, 0.0>
        llWhisper (0, "Position relative to <0,0,0> of 'Da Boom': "+ (string)llRound(vecrel.x) +",\t\t\t"+ (string)llRound(vecrel.y) +",\t\t\t"+ (string)llRound(vecrel.z) + ".");
        llWhisper(0, "Position relative to <0,0,0> of 'Da Boom':"+(string)vecrel ); //faster but unformatted output
    }
}
 

The great zero is at region offset <1000,1000>, Great Zero