Geometric types represent two-dimensional spatial objects. The most fundamental type, the point, forms the basis for all of the other types.
Table 3-18. Postgres Geometric Types
| Geometric Type | Storage | Representation | Description |
|---|---|---|---|
| point | 16 bytes | (x,y) | Point in space |
| line | 32 bytes | ((x1,y1),(x2,y2)) | Infinite line |
| lseg | 32 bytes | ((x1,y1),(x2,y2)) | Finite line segment |
| box | 32 bytes | ((x1,y1),(x2,y2)) | Rectangular box |
| path | 4+32n bytes | ((x1,y1),...) | Closed path (similar to polygon) |
| path | 4+32n bytes | [(x1,y1),...] | Open path |
| polygon | 4+32n bytes | ((x1,y1),...) | Polygon (similar to closed path) |
| circle | 24 bytes | <(x,y),r> | Circle (center and radius) |
A rich set of functions and operators is available to perform various geometric operations such as scaling, translation, rotation, and determining intersections.
Points are the fundamental two-dimensional building block for geometric types.
point is specified using the following syntax:
( x , y )
x , y
where
x is the x-axis coordinate as a floating point number
y is the y-axis coordinate as a floating point number
Line segments (lseg) are represented by pairs of points.
lseg is specified using the following syntax:
( ( x1 , y1 ) , ( x2 , y2 ) )
( x1 , y1 ) , ( x2 , y2 )
x1 , y1 , x2 , y2
where
(x1,y1) and (x2,y2) are the endpoints of the segment
Boxes are represented by pairs of points which are opposite corners of the box.
box is specified using the following syntax:
( ( x1 , y1 ) , ( x2 , y2 ) )
( x1 , y1 ) , ( x2 , y2 )
x1 , y1 , x2 , y2
where
(x1,y1) and (x2,y2) are opposite corners
Boxes are output using the first syntax. The corners are
reordered on input to store the lower left corner first and the
upper right corner last. Other corners of the box can be entered,
but the lower left and upper right corners are determined from the
input and stored.
Paths are represented by connected sets of points. Paths can be "open", where the first and last points in the set are not connected, and "closed", where the first and last point are connected. Functions popen(p) and pclose(p) are supplied to force a path to be open or closed, and functions isopen(p) and isclosed(p) are supplied to select either type in a query.
path is specified using the following syntax:
( ( x1 , y1 ) , ... , ( xn , yn ) )
[ ( x1 , y1 ) , ... , ( xn , yn ) ]
( x1 , y1 ) , ... , ( xn , yn )
( x1 , y1 , ... , xn , yn )
x1 , y1 , ... , xn , yn
where
(x1,y1),...,(xn,yn) are points 1 through n
a leading "[" indicates an open path
a leading "(" indicates a closed path
Paths are output using the first syntax. Note that
Postgres versions prior to v6.1
used a format for paths which had a single leading parenthesis, a
"closed" flag, an integer count of the number of points, then the
list of points followed by a closing parenthesis. The built-in
function upgradepath is supplied to
convert paths dumped and reloaded from pre-v6.1 databases.
Polygons are represented by sets of points. Polygons should probably be considered equivalent to closed paths, but are stored differently and have their own set of support routines.
polygon is specified using the following syntax:
( ( x1 , y1 ) , ... , ( xn , yn ) )
( x1 , y1 ) , ... , ( xn , yn )
( x1 , y1 , ... , xn , yn )
x1 , y1 , ... , xn , yn
where
(x1,y1),...,(xn,yn) are points 1 through n
Polygons are output using the first syntax. Note that
Postgres versions prior to v6.1
used a format for polygons which had a single leading parenthesis,
the list of x-axis coordinates, the list of y-axis coordinates,
followed by a closing parenthesis. The built-in function upgradepoly is supplied to convert polygons dumped
and reloaded from pre-v6.1 databases.
Circles are represented by a center point and a radius.
circle is specified using the following syntax:
< ( x , y ) , r >
( ( x , y ) , r )
( x , y ) , r
x , y , r
where
(x,y) is the center of the circle
r is the radius of the circle
Circles are output using the first syntax.