Name

ST_CurveN — Returns the Nth component curve geometry of a CompoundCurve.

Synopsis

geometry ST_CurveN(geometry a_compoundcurve, integer index);

描述

Returns the Nth component curve geometry of a CompoundCurve. The index starts at 1. Returns NULL if the geometry is not a CompoundCurve or the index is out of range.

该方法实现了SQL/MM规范。 SQL-MM 3: 8.2.6, 8.3.5

该函数支持 3d 并且不会丢失 z-index。

示例

SELECT ST_AsText(ST_CurveN('COMPOUNDCURVE(
    (2 2, 2.5 2.5),
    CIRCULARSTRING(2.5 2.5, 4.5 2.5, 3.5 3.5),
    (3.5 3.5, 2.5 4.5, 3 5, 2 2)
  )', 1));