ST_AsText

Creates the Well-Known Text (WKT) representation of a spatial object. Use this function when you need to specify a spatial object in ASCII form.

The Open Geospatial Consortium (OGC) defines the format of a WKT string in the Simple Feature Access Part 1 - Common Architecture specification.

Behavior Type

Immutable

Syntax

ST_AsText( g )

Arguments

g

Spatial object for which you want the WKT string, type GEOMETRY or GEOGRAPHY

Returns

LONG VARCHAR

Supported Data Types

Data Type GEOMETRY GEOGRAPHY (Perfect Sphere) GEOGRAPHY (WGS84)
Point Yes Yes Yes
Multipoint Yes Yes Yes
Linestring Yes Yes Yes
Multilinestring Yes Yes Yes
Polygon Yes Yes Yes
Multipolygon Yes Yes Yes
GeometryCollection Yes No No

Example

The following example shows how to use ST_AsText.

Retrieve WKB and WKT representations:

=> CREATE TABLE locations (id INTEGER, name VARCHAR(100), geom1 GEOMETRY(800),
   geom2 GEOGRAPHY);
CREATE TABLE
=> COPY locations
    (id, geom1x FILLER LONG VARCHAR(800), geom1 AS ST_GeomFromText(geom1x), geom2x FILLER LONG VARCHAR (800),
     geom2 AS ST_GeographyFromText(geom2x))
    FROM stdin;
Enter data to be copied followed by a newline.
End with a backslash and a period on a line by itself.
>> 1|POINT(2 3)|
>> 2|LINESTRING(2 4,1 5)|
>> 3||POLYGON((-70.96 43.27,-70.67 42.95,-66.90 44.74,-67.81 46.08,-67.81 47.20,-69.22 47.43,-71.09 45.25,-70.96 43.27))
>> \.
=> SELECT id, ST_AsText(geom1),ST_AsText(geom2) FROM locations ORDER BY id ASC;
 id |       ST_AsText       |                 ST_AsText                                                         
----+-----------------------+---------------------------------------------
  1 | POINT (2 3)           | 
  2 | LINESTRING (2 4, 1 5) | 
  3 |                       | POLYGON ((-70.96 43.27, -70.67 42.95, -66.9 44.74, -67.81 46.08, -67.81 47.2, -69.22 47.43, -71.09 45.25, -70.96 43.27))
(3 rows)

Calculate the length of a WKT using the Vertica SQL function LENGTH:

=> SELECT LENGTH(ST_AsText(St_GeomFromText('POLYGON ((-1 2, 0 3, 1 2,
                                                      0 1, -1 2))')));
 LENGTH
--------
     37
(1 row)

See Also