## Name

ST_SimplifyVW — Returns a simplified representation of a geometry, using the Visvalingam-Whyatt algorithm

## Synopsis

`geometry ST_SimplifyVW(`geometry geom, float tolerance`)`;

## 설명

Returns a simplified representation of a geometry using the Visvalingam-Whyatt algorithm. The simplification `tolerance` is an area value, in the units of the input SRS. Simplification removes vertices which form "corners" with area less than the tolerance. The result may not be valid even if the input is.

The function can be called with any kind of geometry (including GeometryCollections), but only line and polygon elements are simplified. Endpoints of linear geometry are preserved.

 The returned geometry may lose its simplicity (see ST_IsSimple), topology may not be preserved, and polygonal results may be invalid (see ST_IsValid). Use ST_SimplifyPreserveTopology to preserve topology and ensure validity. ST_CoverageSimplify also preserves topology and validity.
 This function does not preserve boundaries shared between polygons. Use ST_CoverageSimplify if this is required.
 이 함수는 3차원을 처리하며, 세 번째 차원이 결과에 영향을 미칠 것입니다.

2.2.0 버전부터 사용할 수 있습니다.

## 예시

A LineString is simplified with a minimum-area tolerance of 30.

```SELECT ST_AsText(ST_SimplifyVW(geom,30)) simplified
FROM (SELECT 'LINESTRING(5 2, 3 8, 6 20, 7 25, 10 10)'::geometry AS geom) AS t;

simplified
------------------------------
LINESTRING(5 2,7 25,10 10)
```

Simplifying a line.

```SELECT ST_SimplifyVW(
'LINESTRING (10 10, 50 40, 30 70, 50 60, 70 80, 50 110, 100 100, 90 140, 100 180, 150 170, 170 140, 190 90, 180 40, 110 40, 150 20)',
1600);
```

Simplifying a polygon.

```SELECT ST_SimplifyVW(
'MULTIPOLYGON (((90 110, 80 180, 50 160, 10 170, 10 140, 20 110, 90 110)), ((40 80, 100 100, 120 160, 170 180, 190 70, 140 10, 110 40, 60 40, 40 80), (180 70, 170 110, 142.5 128.5, 128.5 77.5, 90 60, 180 70)))',
40);
```