This topic describes the ST_SimplifyVW function. This function returns a geometry object representing a simplified version of the input geometry object. This function uses the Visvalingam-Whyatt algorithm.

## Syntax

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

## Parameters

Parameter | Description |
---|---|

geomA | The geometry object that you want to specify. |

tolerance | The tolerance that you want to specify. |

## Description

- This function supports simplification operations only on MultiLine objects, MultiPolygon objects, and MultiPoint objects. However, you can use this function to process any geometry objects.
- The simplification operation is performed on the input geometry objects one by one. Therefore, you can use this function to process GeometryCollection objects.
- The returned geometry object may lose its simplicity.
- This function may change the topology of the input geometry object and return an invalid
geometry object.
You can use the ST_SimplifyPreserveTopology function to preserve the topology of the input geometry object.

- This function supports 3D objects, and the 3D dimension of the input geometry object affects the returned geometry object.

## Examples

Comparison between the results of the ST_Simplify function and the ST_SimplifyVW function:

```
select g,ST_Simplify(g,0.5),
ST_SimplifyVW(g,0.5)
from (select 'LINESTRING(0 0,2 2,3 1,3.5 1.5,5 0,5.25 0.25,5.5 0)'::geometry as g) as t;
```