This section lists the PostgreSQL data types installed by PostGIS. Note we describe the casting behavior of these which is very
important especially when designing your own functions.
A Cast is when one type is coerced into another type. PostgreSQL
is unique from most databases in that it allows you to define casting behavior for custom types and the functions used for casting.
A cast can be specified as automatic in which case, you do not have to do a CAST(myfoo As otherfootype) or myfoo::otherfootype
if you are feeding it to a function that only works with otherfootype and there is an automatic cast in place for it.
The danger of relying on automatic cast behavior is when you have an overloaded function say one that takes a box2d and one that takes a box3d
but no geometry. What happens is that both functions are equally good to use with geometry since geometry has an autocast for both
-- so you end up with an ambiguous function error. To force PostgreSQL to choose, you do a CAST(mygeom As box3d) or mygeom::box3d.
At least as of PostgreSQL 8.3 - Everything can be CAST to text (presumably because of the magical unknown type), so no defined CASTS for that need to be present for you to CAST an object to text.
PostgreSQL PostGIS Geometry/Geography/Box Types
box2d
A box composed of x min, ymin, xmax, ymax. Often used to return the 2d enclosing box of a geometry.
Description
box2d is a spatial data type used to represent the enclosing box of a geometry or set of geometries. ST_Extent in earlier versions prior to PostGIS 1.4 would return a box2d.
box3d
A box composed of x min, ymin, zmin, xmax, ymax, zmax. Often used to return the 3d extent of a geometry or collection of geometries.
Description
box3d is a postgis spatial data type used to represent the enclosing box of a geometry or set of geometries. ST_3DExtent returns a box3d object.
Casting Behavior
This section lists the automatic as well as explicit casts allowed for this data type
Cast To
Behavior
box
automatic
box2d
automatic
geometry
automatic
geometry
Planar spatial data type.
Description
geometry is a fundamental postgis spatial data type used to represent a feature in the Euclidean coordinate system.
Casting Behavior
This section lists the automatic as well as explicit casts allowed for this data type
Cast To
Behavior
box
automatic
box2d
automatic
box3d
automatic
bytea
automatic
geography
automatic
text
automatic
See Also
geometry_dump
A spatial datatype with two fields - geom (holding a geometry object)
and path[] (a 1-d array holding the position of the geometry within the dumped object.)
Description
geometry_dump is a compound data type consisting of a geometry object referenced by the .geom field
and path[] a 1-dimensional integer array (starting at 1 e.g. path[1] to get first element) array that defines the navigation path within the dumped geometry to find this element.
It is used by the ST_Dump* family of functions as an output type to explode a more complex geometry into its
constituent parts and location of parts.
See Also
geography
Ellipsoidal spatial data type.
Description
geography is a spatial data type used to represent a feature in the round-earth coordinate system.
Casting Behavior
This section lists the automatic as well as explicit casts allowed for this data type
Cast To
Behavior
geometry
explicit
See Also
,