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. 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 the arguments are
The x-axis coordinate as a floating-point number
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 the arguments are
The end points of the line segment
Boxes are represented by pairs of points that 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 the arguments are
Opposite corners of the box
Boxes are output using the first syntax. The corners are reordered on input to store the upper right corner, then the lower left corner. 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 test for 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 the arguments are
End points of the line segments comprising the path. A leading square bracket ("[") indicates an open path, while a leading parenthesis ("(") indicates a closed path.
Paths are output using the first syntax.
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 the arguments are
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 a radius.
circle is specified using the following syntax:
< ( x , y ) , r >
( ( x , y ) , r )
( x , y ) , r
x , y , r
where the arguments are
Center of the circle
Radius of the circle
Circles are output using the first syntax.