This topic describes the ST_AsEWKB function. This function returns the Well-Known Binary (WKB) string that represents a geometry object or a geography object. The WKB string that is returned contains spatial reference identifier (SRID) metadata.

Syntax

bytea  ST_AsEWKB(geometry  g1);
bytea  ST_AsEWKB(geometry  g1 , text  NDRorXDR);
bytea  ST_AsEWKB(geography  g1);
bytea  ST_AsEWKB(geography  g1 , text  NDRorXDR);

Parameters

Parameter Description
g1 The geometry object or geography object whose WKB representation you want to obtain.
NDRorXDR The byte order that you want to use. Valid values:
  • XDR: big endian.
  • NDR: little endian. This is the default value.

Description

  • The WKB specification defines that standard WKB strings do not contain SRIDs. If you want to obtain a WKB string that contains an SRID, use this function.
  • This function supports circular strings, curves, polyhedral surfaces, triangles, triangulated irregular network (TIN) surfaces, and 3D objects.

Examples

  • Obtain a WKB string with the default little endian byte order retained.
    SELECT ST_AsEWKB(ST_GeomFromText('POLYGON((1 1,1 2,2 2,2 1,1 1))',4326));
                           st_asewkb
---------------------------------------------------------------
 \x0103000020e61000000100000005000000000000000000f03f000000000.
.000f03f000000000000f03f00000000000000400000000000000040000000.
.00000000400000000000000040000000000000f03f000000000000f03f000.
.000000000f03f
(1 row)
  • Obtain a WKB string with the big endian byte order specified.
    SELECT ST_AsEWKB(ST_GeomFromText('POLYGON((1 1,1 2,2 2,2 1,1 1))',4326),'XDR');
                           st_asewkb
---------------------------------------------------------------
 \x0020000003000010e600000001000000053ff00000000000003ff000000.
.00000003ff000000000000040000000000000004000000000000000400000.
.000000000040000000000000003ff00000000000003ff00000000000003ff.
.0000000000000
(1 row)