## Name

ST_LineToCurve — 将线性几何图形转换为曲线几何图形。

## Synopsis

`geometry ST_LineToCurve(`geometry geomANoncircular`)`;

## 描述

 如果输入线串/多边形不足以清楚地表示曲线，则该函数返回与输入几何图形相同的值。

## 示例

```-- 2D Example
SELECT ST_AsText(ST_LineToCurve(foo.geom)) As curvedastext,ST_AsText(foo.geom) As non_curvedastext
FROM (SELECT ST_Buffer('POINT(1 3)'::geometry, 3) As geom) As foo;

curvedatext                                                            non_curvedastext
--------------------------------------------------------------------|-----------------------------------------------------------------
CURVEPOLYGON(CIRCULARSTRING(4 3,3.12132034355964 0.878679656440359, | POLYGON((4 3,3.94235584120969 2.41472903395162,3.77163859753386 1.85194970290473,
1 0,-1.12132034355965 5.12132034355963,4 3))                        |  3.49440883690764 1.33328930094119,3.12132034355964 0.878679656440359,
|  2.66671069905881 0.505591163092366,2.14805029709527 0.228361402466141,
|  1.58527096604839 0.0576441587903094,1 0,
|  0.414729033951621 0.0576441587903077,-0.148050297095264 0.228361402466137,
|  -0.666710699058802 0.505591163092361,-1.12132034355964 0.878679656440353,
|  -1.49440883690763 1.33328930094119,-1.77163859753386 1.85194970290472
|  --ETC-- ,3.94235584120969 3.58527096604839,4 3))

--3D example
SELECT ST_AsText(ST_LineToCurve(geom)) As curved, ST_AsText(geom) AS not_curved
FROM (SELECT ST_Translate(ST_Force3D(ST_Boundary(ST_Buffer(ST_Point(1,3), 2,2))),0,0,3) AS geom) AS foo;

curved                        |               not_curved
------------------------------------------------------+---------------------------------------------------------------------
CIRCULARSTRING Z (3 3 3,-1 2.99999999999999 3,3 3 3) | LINESTRING Z (3 3 3,2.4142135623731 1.58578643762691 3,1 1 3,
| -0.414213562373092 1.5857864376269 3,-1 2.99999999999999 3,
| -0.414213562373101 4.41421356237309 3,
| 0.999999999999991 5 3,2.41421356237309 4.4142135623731 3,3 3 3)
(1 row)
```