9.11. 地理資訊函式及運算子
The geometric types
point,box,lseg,line,path,polygon, andcirclehave a large set of native support functions and operators, shown inTable 9.33,Table 9.34, andTable 9.35.Note that the“same as”operator,
~=, represents the usual notion of equality for thepoint,box,polygon, andcircletypes. Some of these types also have an=operator, but=compares for equal_areas_only. The other scalar comparison operators (<=and so on) likewise compare areas for these types.Table 9.33. Geometric Operators
Operator | Description | Example | Text | Text | Text | Text |
|---|---|---|---|---|---|---|
+ | 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)' | | | | |
# | Point or box of intersection | box '((1,-1),(-1,1))' # box '((1,1),(-2,-2))' | | | | |
# | Number of points in path or polygon | # path '((1,0),(0,1),(-1,0))' | | | | |
@-@ | Length or circumference | @-@ path '((0,0),(1,0))' | | | | |
@@ | Center | @@ circle '((0,0),10)' | | | | |
## | Closest point to first operand on second operand | point '(0,0)' ## lseg '((2,0),(0,2))' | | | | |
<-> | Distance between | circle '((0,0),1)' <-> circle '((5,0),1)' | | | | |
&& | Overlaps? (One point in common makes this true.) | box '((0,0),(1,1))' && box '((0,0),(2,2))' | | | | |
<< | Is strictly left of? | circle '((0,0),1)' << circle '((5,0),1)' | | | | |
>> | Is strictly right of? | circle '((5,0),1)' >> circle '((0,0),1)' | | | | |
&< | Does not extend to the right of? | box '((0,0),(1,1))' &< box '((0,0),(2,2))' | | | | |
&> | Does not extend to the left of? | box '((0,0),(3,3))' &> box '((0,0),(2,2))' | | | | |
`<< | ` | Is strictly below? | `box '((0,0),(3,3))' << | box '((3,4),(5,5))'` | | |
` | >>` | Is strictly above? | `box '((3,4),(5,5))' | >> box '((0,0),(3,3))'` | | |
`&< | ` | Does not extend above? | `box '((0,0),(1,1))' &< | box '((0,0),(2,2))'` | | |
` | &>` | Does not extend below? | `box '((0,0),(3,3))' | &> box '((0,0),(2,2))'` | | |
<^ | Is below (allows touching)? | circle '((0,0),1)' <^ circle '((0,5),1)' | | | | |
>^ | Is above (allows touching)? | circle '((0,5),1)' >^ circle '((0,0),1)' | | | | |
?# | Intersects? | lseg '((-1,0),(1,0))' ?# box '((-2,-2),(2,2))' | | | | |
?- | Is horizontal? | ?- lseg '((-1,0),(1,0))' | | | | |
?- | Are horizontally aligned? | point '(1,0)' ?- point '(0,0)' | | | | |
`? | ` | Is vertical? | `? | lseg '((-1,0),(1,0))'` | | |
`? | ` | Are vertically aligned? | `point '(0,1)' ? | point '(0,0)'` | | |
`?- | ` | Is perpendicular? | `lseg '((0,0),(0,1))' ?- | lseg '((0,0),(1,0))'` | | |
`? | | ` | Are parallel? | `lseg '((-1,0),(1,0))' ? | | lseg '((-1,2),(1,2))'` |
@> | Contains? | circle '((0,0),2)' @> point '(1,1)' | | | | |
<@ | Contained in or on? | point '(1,1)' <@ circle '((0,0),2)' | | | | |
~= | Same as? | polygon '((0,0),(1,1))' ~= polygon '((1,1),(0,0))' | | | | |
BeforePostgreSQL8.2, the containment operators
@>and<@were respectively called~and@. These names are still available, but are deprecated and will eventually be removed.Table 9.34. Geometric Functions
Function | Return Type | Description | Example |
|---|---|---|---|
area(object) | double precision | area | area(box '((0,0),(1,1))') |
center(object) | point | center | 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 | length(path '((-1,0),(1,0))') |
npoints(path) | int | number of points | npoints(path '[(0,0),(1,1),(2,0)]') |
npoints(polygon) | int | number of points | npoints(polygon '((1,1),(0,0))') |
pclose(path) | path | convert path to closed | pclose(path '[(0,0),(1,1),(2,0)]') |
popen(path) | path | convert path to open | 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 of box | width(box '((0,0),(1,1))') |
Table 9.35. Geometric Type Conversion Functions
Function | Return Type | Description | Example |
|---|---|---|---|
box(circle) | box | circle to box | box(circle '((0,0),2.0)') |
box(point) | box | point to empty box | box(point '(0,0)') |
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))') |
bound_box(box,box) | box | boxes to bounding box | bound_box(box '((0,0),(1,1))', box '((3,3),(4,4))') |
circle(box) | circle | box to circle | circle(box '((0,0),(1,1))') |
circle(point,double precision) | circle | center and radius to circle | circle(point '(0,0)', 2.0) |
circle(polygon) | circle | polygon to circle | circle(polygon '((0,0),(1,1),(2,0))') |
line(point,point) | line | points to line | line(point '(-1,0)', point '(1,0)') |
lseg(box) | lseg | box diagonal to line segment | lseg(box '((-1,0),(1,0))') |
lseg(point,point) | lseg | points to line segment | lseg(point '(-1,0)', point '(1,0)') |
path(polygon) | path | polygon to path | path(polygon '((0,0),(1,1),(2,0))') |
point(double precision,double precision) | point | construct point | point(23.4, -44.5) |
point(box) | point | center of box | point(box '((-1,0),(1,0))') |
point(circle) | point | center of circle | point(circle '((0,0),2.0)') |
point(lseg) | point | center of line segment | point(lseg '((-1,0),(1,0))') |
point(polygon) | point | center of polygon | point(polygon '((0,0),(1,1),(2,0))') |
polygon(box) | polygon | box to 4-point polygon | polygon(box '((0,0),(1,1))') |
polygon(circle) | polygon | circle to 12-point polygon | polygon(circle '((0,0),2.0)') |
polygon(npts,circle) | polygon | circle to npts-point 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
pointas though the point were an array with indexes 0 and 1. For example, ift.pis apointcolumn thenSELECT p[0] FROM tretrieves the X coordinate andUPDATE t SET p[1] = ...changes the Y coordinate. In the same way, a value of typeboxorlsegcan be treated as an array of twopointvalues.The
areafunction works for the typesbox,circle, andpath. Theareafunction only works on thepathdata type if the points in thepathare non-intersecting. For example, thepath'((0,0),(0,1),(2,1),(2,2),(1,2),(1,0),(0,0))'::PATHwill not work; however, the following visually identicalpath'((0,0),(0,1),(1,1),(1,2),(2,2),(2,1),(1,1),(1,0),(0,0))'::PATHwill work. If the concept of an intersecting versus non-intersectingpathis confusing, draw both of the abovepaths side by side on a piece of graph paper.