Geometric data types represent two-dimensional spatial objects. Table 8.20 shows the geometric types available in PostgreSQL.
Table 8.20. Geometric Types
| Name | Storage Size | Description | Representation |
|---|---|---|---|
point | 16 bytes | Point on a plane | (x,y) |
line | 24 bytes | Infinite line | {A,B,C} |
lseg | 32 bytes | Finite line segment | ((x1,y1),(x2,y2)) |
box | 32 bytes | Rectangular box | ((x1,y1),(x2,y2)) |
path | 16+16n bytes | Closed path (similar to polygon) | ((x1,y1),...) |
path | 16+16n bytes | Open path | [(x1,y1),...] |
polygon | 40+16n bytes | Polygon (similar to closed path) | ((x1,y1),...) |
circle | 24 bytes | Circle | <(x,y),r> (center point and radius) |
In all these types, the individual coordinates are stored as
double precision (float8) numbers.
A rich set of functions and operators is available to perform various geometric operations such as scaling, translation, rotation, and determining intersections. They are explained in Section 9.11.
Points are the fundamental two-dimensional building block for geometric
types. Values of type point are specified using either of
the following syntaxes:
(x,y)x,y
where x and y are the respective
coordinates, as floating-point numbers.
Points are output using the first syntax.
Lines are represented by the linear
equation Ax + By + C = 0,
where A and B are not both zero. Values
of type line are input and output in the following form:
{ A, B, C }
Alternatively, any of the following forms can be used for input:
[ (x1,y1) , (x2,y2) ] ( (x1,y1) , (x2,y2) ) (x1,y1) , (x2,y2)x1,y1,x2,y2
where
(
and
x1,y1)(
are two different points on the line.
x2,y2)
Line segments are represented by pairs of points that are the endpoints
of the segment. Values of type lseg are specified using any
of the following syntaxes:
[ (x1,y1) , (x2,y2) ] ( (x1,y1) , (x2,y2) ) (x1,y1) , (x2,y2)x1,y1,x2,y2
where
(
and
x1,y1)(
are the end points of the line segment.
x2,y2)
Line segments are output using the first syntax.
Boxes are represented by pairs of points that are opposite
corners of the box.
Values of type box are specified using any of the following
syntaxes:
( (x1,y1) , (x2,y2) ) (x1,y1) , (x2,y2)x1,y1,x2,y2
where
(
and
x1,y1)(
are any two opposite corners of the box.
x2,y2)
Boxes are output using the second syntax.
Any two opposite corners can be supplied on input, but the values will be reordered as needed to store the upper right and lower left corners, in that order.
Paths are represented by lists of connected points. Paths can be open, where the first and last points in the list are considered not connected, or closed, where the first and last points are considered connected.
Values of type path are specified using any of the following
syntaxes:
[ (x1,y1) , ... , (xn,yn) ] ( (x1,y1) , ... , (xn,yn) ) (x1,y1) , ... , (xn,yn) (x1,y1, ... ,xn,yn)x1,y1, ... ,xn,yn
where the points are the end points of the line segments
comprising the path. Square brackets ([]) indicate
an open path, while parentheses (()) indicate a
closed path. When the outermost parentheses are omitted, as
in the third through fifth syntaxes, a closed path is assumed.
Paths are output using the first or second syntax, as appropriate.
Polygons are represented by lists of points (the vertexes of the polygon). Polygons are very similar to closed paths; the essential semantic difference is that a polygon is considered to include the area within it, while a path is not.
An important implementation difference between polygons and paths is that the stored representation of a polygon includes its smallest bounding box. This speeds up certain search operations, although computing the bounding box adds overhead while constructing new polygons.
Values of type polygon are specified using any of the
following syntaxes:
( (x1,y1) , ... , (xn,yn) ) (x1,y1) , ... , (xn,yn) (x1,y1, ... ,xn,yn)x1,y1, ... ,xn,yn
where the points are the end points of the line segments comprising the boundary of the polygon.
Polygons are output using the first syntax.
Circles are represented by a center point and radius.
Values of type circle are specified using any of the
following syntaxes:
< (x,y) ,r> ( (x,y) ,r) (x,y) ,rx,y,r
where
(
is the center point and x,y)r is the radius of the
circle.
Circles are output using the first syntax.