ST_Envelope
Name
ST_Envelope — Returns the polygon representation of the extent of the raster.
Synopsis
    
     geometry
     
      ST_Envelope
     
     (
    
    raster
    
     rast
    
    
     )
    
    ;
   
Description
Returns the polygon representation of the extent of the raster in spatial coordinate units defined by srid. It is a float8 minimum bounding box represented as a polygon.
   The polygon is defined by the corner points of the bounding box
            ((
   
    MINX
   
   ,
   
    MINY
   
   ),
            (
   
    MINX
   
   ,
   
    MAXY
   
   ),
            (
   
    MAXX
   
   ,
   
    MAXY
   
   ),
            (
   
    MAXX
   
   ,
   
    MINY
   
   ),
            (
   
    MINX
   
   ,
   
    MINY
   
   ))
  
Examples
SELECT rid, ST_AsText(ST_Envelope(rast)) As envgeomwkt
FROM dummy_rast;
 rid |                                         envgeomwkt
-----+--------------------------------------------------------------------
   1 | POLYGON((0 0,20 0,20 60,0 60,0 0))
   2 | POLYGON((3427927 5793243,3427928 5793243,
        3427928 5793244,3427927 5793244, 3427927 5793243))