161 lines
3.9 KiB
Markdown
161 lines
3.9 KiB
Markdown
---
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sidebar_label: Geometry Functions
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title: Geometry Functions
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toc_max_heading_level: 4
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---
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## Geometry Input Functions
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Geometry input functions create geometry data from WTK.
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### ST_GeomFromText
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```sql
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ST_GeomFromText(VARCHAR WKT expr)
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```
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**Description**: Return a specified GEOMETRY value from Well-Known Text representation (WKT).
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**Return value type**: GEOMETRY
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**Applicable data types**: VARCHAR
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**Applicable table types**: standard tables and supertables
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**Explanations**：
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- The input can be one of WTK string, like POINT, LINESTRING, POLYGON, MULTIPOINT, MULTILINESTRING, MULTIPOLYGON, GEOMETRYCOLLECTION.
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- The output is a GEOMETRY data type, internal defined as binary string.
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## Geometry Output Functions
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Geometry output functions convert geometry data into WTK.
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### ST_AsText
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```sql
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ST_AsText(GEOMETRY geom)
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```
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**Description**: Return a specified Well-Known Text representation (WKT) value from GEOMETRY data.
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**Return value type**: VARCHAR
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**Applicable data types**: GEOMETRY
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**Applicable table types**: standard tables and supertables
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**Explanations**：
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- The output can be one of WTK string, like POINT, LINESTRING, POLYGON, MULTIPOINT, MULTILINESTRING, MULTIPOLYGON, GEOMETRYCOLLECTION.
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## Geometry Relationships Functions
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Geometry relationships functions determine spatial relationships between geometries.
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### ST_Intersects
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```sql
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ST_Intersects(GEOMETRY geomA, GEOMETRY geomB)
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```
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**Description**: Compares two geometries and returns true if they intersect.
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**Return value type**: BOOL
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**Applicable data types**: GEOMETRY, GEOMETRY
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**Applicable table types**: standard tables and supertables
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**Explanations**：
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- Geometries intersect if they have any point in common.
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### ST_Equals
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```sql
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ST_Equals(GEOMETRY geomA, GEOMETRY geomB)
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```
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**Description**: Returns TRUE if the given geometries are "spatially equal".
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**Return value type**: BOOL
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**Applicable data types**: GEOMETRY, GEOMETRY
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**Applicable table types**: standard tables and supertables
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**Explanations**：
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- 'Spatially equal' means ST_Contains(A,B) = true and ST_Contains(B,A) = true, and the ordering of points can be different but represent the same geometry structure.
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### ST_Touches
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```sql
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ST_Touches(GEOMETRY geomA, GEOMETRY geomB)
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```
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**Description**: Returns TRUE if A and B intersect, but their interiors do not intersect.
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**Return value type**: BOOL
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**Applicable data types**: GEOMETRY, GEOMETRY
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**Applicable table types**: standard tables and supertables
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**Explanations**：
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- A and B have at least one point in common, and the common points lie in at least one boundary.
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- For Point/Point inputs the relationship is always FALSE, since points do not have a boundary.
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### ST_Covers
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```sql
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ST_Covers(GEOMETRY geomA, GEOMETRY geomB)
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```
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**Description**: Returns TRUE if every point in Geometry B lies inside (intersects the interior or boundary of) Geometry A.
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**Return value type**: BOOL
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**Applicable data types**: GEOMETRY, GEOMETRY
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**Applicable table types**: standard tables and supertables
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**Explanations**：
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- A covers B means no point of B lies outside (in the exterior of) A.
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### ST_Contains
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```sql
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ST_Contains(GEOMETRY geomA, GEOMETRY geomB)
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```
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**Description**: Returns TRUE if geometry A contains geometry B.
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**Return value type**: BOOL
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**Applicable data types**: GEOMETRY, GEOMETRY
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**Applicable table types**: standard tables and supertables
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**Explanations**：
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- A contains B if and only if all points of B lie inside (i.e. in the interior or boundary of) A (or equivalently, no points of B lie in the exterior of A), and the interiors of A and B have at least one point in common.
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### ST_ContainsProperly
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```sql
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ST_ContainsProperly(GEOMETRY geomA, GEOMETRY geomB)
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```
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**Description**: Returns TRUE if every point of B lies inside A.
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**Return value type**: BOOL
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**Applicable data types**: GEOMETRY, GEOMETRY
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**Applicable table types**: standard tables and supertables
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**Explanations**：
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- There is no point of B lies in the the boundary or exterior of A.
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