ST_Knots
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Name

ST_Knots — Returns the knot vector of a NURBS curve.

Synopsis

float8[] ST_Knots(geometry nurbscurve);

描述

Returns the knot vector of a NURBS curve as an array of double precision values. The knot vector defines the parameter space and controls where and how the control points affect the curve. It must be a non-decreasing sequence with length equal to (number of control points + degree + 1).

Returns NULL if the curve uses the default uniform clamped knot vector or if the input is NULL. Raises an error if the input is not a NURBS curve.

Availability: 3.7.0

示例

This example returns knots from a NURBS curve with a custom knot vector.

SELECT ST_Knots(ST_MakeNurbsCurve(
                2,
                'LINESTRING(0 0, 5 10, 10 0)'::geometry,
                ARRAY[1.0, 2.0, 1.0],
                ARRAY[0,0,0,1,1,1]));
{0,0,0,1,1,1}

This example checks the knots of a curve using the default knot vector.

SELECT ST_Knots('NURBSCURVE(2, (0 0, 5 10, 10 0))'::geometry);
null