Geometric Functions and Operators

PostgreSQL 7.3.4 Documentation
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# 6.9. Geometric Functions and Operators

The geometric types `point`, `box`, `lseg`, `line`, `path`, `polygon`, and `circle` have a large set of native support functions and operators, shown in Table 6-20, Table 6-21, and Table 6-22.

Table 6-20. Geometric Operators

Operator | Description | Usage
--- | --- | ---
+ | Translation | box '((0,0),(1,1))' + point '(2.0,0)'
- | Translation | box '((0,0),(1,1))' - point '(2.0,0)'
* | Scaling/rotation | box '((0,0),(1,1))' * point '(2.0,0)'
/ | Scaling/rotation | box '((0,0),(2,2))' / point '(2.0,0)'
# | Intersection | '((1,-1),(-1,1))' # '((1,1),(-1,-1))'
# | Number of points in path or polygon | # '((1,0),(0,1),(-1,0))'
## | Point of closest proximity | point '(0,0)' ## lseg '((2,0),(0,2))'
&& | Overlaps? | box '((0,0),(1,1))' && box '((0,0),(2,2))'
&< | Overlaps to left? | box '((0,0),(1,1))' &< box '((0,0),(2,2))'
&> | Overlaps to right? | box '((0,0),(3,3))' &> box '((0,0),(2,2))'
<-> | Distance between | circle '((0,0),1)' <-> circle '((5,0),1)'
<< | Left of? | circle '((0,0),1)' << circle '((5,0),1)'
<^ | Is below? | circle '((0,0),1)' <^ circle '((0,5),1)'
>> | Is right of? | circle '((5,0),1)' >> circle '((0,0),1)'
>^ | Is above? | circle '((0,5),1)' >^ circle '((0,0),1)'
?# | Intersects or overlaps | lseg '((-1,0),(1,0))' ?# box '((-2,-2),(2,2))'
?- | Is horizontal? | point '(1,0)' ?- point '(0,0)'
?-| | Is perpendicular? | lseg '((0,0),(0,1))' ?-| lseg '((0,0),(1,0))'
@-@ | Length or circumference | @-@ path '((0,0),(1,0))'
?| | Is vertical? | point '(0,1)' ?| point '(0,0)'
?|| | Is parallel? | lseg '((-1,0),(1,0))' ?|| lseg '((-1,2),(1,2))'
@ | Contained or on | point '(1,1)' @ circle '((0,0),2)'
@@ | Center of | @@ circle '((0,0),10)'
~= | Same as | polygon '((0,0),(1,1))' ~= polygon '((1,1),(0,0))'

Table 6-21. Geometric Functions

Function | Returns | Description | Example
--- | --- | --- | ---
`area`(object) | `double precision` | area of item | area(box '((0,0),(1,1))')
`box`(box, box) | `box` | intersection box | box(box '((0,0),(1,1))',box '((0.5,0.5),(2,2))')
`center`(object) | `point` | center of item | center(box '((0,0),(1,2))')
`diameter`(circle) | `double precision` | diameter of circle | diameter(circle '((0,0),2.0)')
`height`(box) | `double precision` | vertical size of box | height(box '((0,0),(1,1))')
`isclosed`(path) | `boolean` | a closed path? | isclosed(path '((0,0),(1,1),(2,0))')
`isopen`(path) | `boolean` | an open path? | isopen(path '[(0,0),(1,1),(2,0)]')
`length`(object) | `double precision` | length of item | length(path '((-1,0),(1,0))')
`npoints`(path) | `integer` | number of points | npoints(path '[(0,0),(1,1),(2,0)]')
`npoints`(polygon) | `integer` | number of points | npoints(polygon '((1,1),(0,0))')
`pclose`(path) | `path` | convert path to closed | popen(path '[(0,0),(1,1),(2,0)]')
`popen`(path) | `path` | convert path to open path | popen(path '((0,0),(1,1),(2,0))')
`radius`(circle) | `double precision` | radius of circle | radius(circle '((0,0),2.0)')
`width`(box) | `double precision` | horizontal size | width(box '((0,0),(1,1))')

Table 6-22. Geometric Type Conversion Functions

Function | Returns | Description | Example
--- | --- | --- | ---
`box`(`circle`) | `box` | circle to box | box(circle '((0,0),2.0)')
`box`(`point`, `point`) | `box` | points to box | box(point '(0,0)', point '(1,1)')
`box`(`polygon`) | `box` | polygon to box | box(polygon '((0,0),(1,1),(2,0))')
`circle`(`box`) | `circle` | to circle | circle(box '((0,0),(1,1))')
`circle`(`point`, `double precision`) | `circle` | point to circle | circle(point '(0,0)', 2.0)
`lseg`(`box`) | `lseg` | box diagonal to `lseg` | lseg(box '((-1,0),(1,0))')
`lseg`(`point`, `point`) | `lseg` | points to `lseg` | lseg(point '(-1,0)', point '(1,0)')
`path`(`polygon`) | `point` | polygon to path | path(polygon '((0,0),(1,1),(2,0))')
`point`(`circle`) | `point` | center | point(circle '((0,0),2.0)')
`point`(`lseg`, `lseg`) | `point` | intersection | point(lseg '((-1,0),(1,0))', lseg '((-2,-2),(2,2))')
`point`(`polygon`) | `point` | center | point(polygon '((0,0),(1,1),(2,0))')
`polygon`(`box`) | `polygon` | 4-point polygon | polygon(box '((0,0),(1,1))')
`polygon`(`circle`) | `polygon` | 12-point polygon | polygon(circle '((0,0),2.0)')
`polygon`(npts, `circle`) | `polygon` | npts polygon | polygon(12, circle '((0,0),2.0)')
`polygon`(`path`) | `polygon` | path to polygon | polygon(path '((0,0),(1,1),(2,0))')

It is possible to access the two component numbers of a `point` as though it were an array with subscripts 0, 1. For example, if t.p is a `point` column then SELECT p[0] FROM t retrieves the X coordinate; UPDATE t SET p[1] = ... changes the Y coordinate. In the same way, a `box` or an `lseg` may be treated as an array of two `point`s.

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