Categories:

地理空間関数

ST_SYMDIFFERENCE

Given two input GEOGRAPHY objects, returns a GEOGRAPHY object that represents the set of points from both input objects that are not part of the intersection of the objects (i.e. the symmetric difference of the two objects).

See also:

ST_INTERSECTION , ST_UNION , ST_DIFFERENCE

Syntax

ST_SYMDIFFERENCE( <geography_expression_1> , <geography_expression_2> )

Arguments

geography_expression_1

A GEOGRAPHY object.

geography_expression_2

A GEOGRAPHY object.

Returns

The function returns a value of type GEOGRAPHY.

If geography_expression_1 and geography_expression_2 are equal (i.e. the symmetric difference is an empty set of points), the function returns NULL.

Usage Notes

  • If any vertex of one input object is on the boundary of the other input object (excluding the vertices), the output might not be accurate.

  • The function is not guaranteed to produce normalized and/or minimal results. For example, an output could consist of a LineString containing several Points that actually forms just one straight segment.

Examples

The following example returns a GEOGRAPHY object that represents the symmetric difference between two input GEOGRAPHY objects:

ALTER SESSION SET GEOGRAPHY_OUTPUT_FORMAT = 'WKT';

SELECT ST_SYMDIFFERENCE(
  TO_GEOGRAPHY('POLYGON((0 0, 1 0, 2 1, 1 2, 2 3, 1 4, 0 4, 0 0))'),
  TO_GEOGRAPHY('POLYGON((3 0, 3 4, 2 4, 1 3, 2 2, 1 1, 2 0, 3 0))')
) AS symmetric_difference_between_objects;

This example produces the following output:

+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| SYMMETRIC_DIFFERENCE_BETWEEN_OBJECTS                                                                                                                                                                                    |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| MULTIPOLYGON(((1 1,1.5 1.500171359,1 2,1.5 2.500285599,1 3,1.5 3.500399839,1 4,0 4,0 0,1 0,1.5 0.5000571198,1 1)),((3 0,3 4,2 4,1.5 3.500399839,2 3,1.5 2.500285599,2 2,1.5 1.500171359,2 1,1.5 0.5000571198,2 0,3 0))) |
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

The following images illustrate the differences in the areas that represent the input and output objects:

Input

Output

Areas of input objects passed to ST_SYMDIFFERENCE Areas of output objects returned by ST_SYMDIFFERENCE
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