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QwtSpline(3) | Qwt User's Guide | QwtSpline(3) |

# NAME¶

QwtSpline - Base class for all splines.

# SYNOPSIS¶

#include <qwt_spline.h>

Inherited by **QwtSplineBasis**, and
**QwtSplineInterpolating**.

## Public Types¶

enum **BoundaryType** { **ConditionalBoundaries**,
**PeriodicPolygon**, **ClosedPolygon** }

enum **BoundaryPosition** { **AtBeginning**, **AtEnd** }

enum **BoundaryCondition** { **Clamped1**, **Clamped2**,
**Clamped3**, **LinearRunout** }

Boundary condition.

## Public Member Functions¶

**QwtSpline** ()

Constructor. virtual **~QwtSpline** ()

Destructor. void **setParametrization** (int type)

void **setParametrization** (**QwtSplineParametrization** *)

const **QwtSplineParametrization** * **parametrization** () const

void **setBoundaryType** (**BoundaryType**)

**BoundaryType** **boundaryType** () const

void **setBoundaryValue** (**BoundaryPosition**, double value)

Define the boundary value. double **boundaryValue**
(**BoundaryPosition**) const

void **setBoundaryCondition** (**BoundaryPosition**, int condition)

Define the condition for an endpoint of the spline. int
**boundaryCondition** (**BoundaryPosition**) const

void **setBoundaryConditions** (int condition, double valueBegin=0.0,
double valueEnd=0.0)

Define the condition at the endpoints of a spline. virtual QPolygonF
**polygon** (const QPolygonF &, double tolerance) const

Interpolate a curve by a polygon. virtual QPainterPath **painterPath**
(const QPolygonF &) const =0

virtual uint **locality** () const

# Detailed Description¶

Base class for all splines.

A spline is a curve represented by a sequence of polynomials. Spline approximation is the process of finding polynomials for a given set of points. When the algorithm preserves the initial points it is called interpolating.

Splines can be classified according to conditions of the polynomials that are met at the start/endpoints of the pieces:

- •
- Geometric Continuity

- •
- G0: polynomials are joined
- •
- G1: first derivatives are proportional at the join point The curve tangents thus have the same direction, but not necessarily the same magnitude. i.e., C1'(1) = (a,b,c) and C2'(0) = (k*a, k*b, k*c).
- •
- G2: first and second derivatives are proportional at join point

- •
- Parametric Continuity

- •
- C0: curves are joined
- •
- C1: first derivatives equal
- •
- C2: first and second derivatives are equal

Geometric continuity requires the geometry to be continuous, while parametric continuity requires that the underlying parameterization be continuous as well. Parametric continuity of order n implies geometric continuity of order n, but not vice-versa.

**QwtSpline** is the base class for spline approximations of
any continuity.

Definition at line 57 of file qwt_spline.h.

# Member Enumeration Documentation¶

## enum QwtSpline::BoundaryCondition¶

Boundary condition. A spline algorithm calculates polynomials by
looking a couple of points back/ahead ( **locality()** ). At the ends
additional rules are necessary to compensate the missing points.

**See also**

**boundaryCondition()**,

**boundaryValue()**

**QwtSplineC2::BoundaryConditionC2**

**Enumerator**

*Clamped1*- The first derivative at the end point is given

**See also**

**boundaryValue()**

*Clamped2*- The second derivative at the end point is given

**See also**

**boundaryValue()**

**Note**

*Clamped3*- The third derivative at the end point is given

**See also**

**boundaryValue()**

**Note**

*LinearRunout*- The first derivate at the endpoint is related to the first derivative at its neighbour by the boundary value. F,e when the boundary value at the end is 1.0 then the slope at the last 2 points is the same.

**See also**

**boundaryValue()**.

Definition at line 119 of file qwt_spline.h.

## enum QwtSpline::BoundaryPosition¶

position of a boundary condition

**See also**

**boundaryCondition()**,

**boundaryValue()**

**Enumerator**

*AtBeginning*- the condition is at the beginning of the polynomial
*AtEnd*- the condition is at the end of the polynomial

Definition at line 99 of file qwt_spline.h.

## enum QwtSpline::BoundaryType¶

Boundary type specifying the spline at its endpoints

**See also**

**setBoundaryType()**,

**boundaryType()**

**Enumerator**

*ConditionalBoundaries*- The polynomials at the start/endpoint depend on specific conditions

**See also**

**QwtSpline::BoundaryCondition**

*PeriodicPolygon*- The polynomials at the start/endpoint are found by using imaginary additional points. Additional points at the end are found by translating points from the beginning or v.v.
*ClosedPolygon*- ClosedPolygon is similar to PeriodicPolygon beside, that the interpolation includes the connection between the last and the first control point.

**Note**

**QwtSplineParametrization::ParameterX**and

**QwtSplineParametrization::ParameterY**

Definition at line 65 of file qwt_spline.h.

# Constructor & Destructor Documentation¶

## QwtSpline::QwtSpline ()¶

Constructor. The default setting is a non closing spline with chordal parametrization

**See also**

**setParametrization()**,

**setBoundaryType()**

Definition at line 540 of file qwt_spline.cpp.

# Member Function Documentation¶

## int QwtSpline::boundaryCondition (BoundaryPosition position) const¶

**Returns**

**Parameters**

*position*At the beginning or the end of the spline

**See also**

**setBoundaryCondition()**,

**boundaryValue()**,

**setBoundaryConditions()**

Definition at line 651 of file qwt_spline.cpp.

## QwtSpline::BoundaryType QwtSpline::boundaryType () const¶

**Returns**

**See also**

**setBoundaryType()**

Definition at line 626 of file qwt_spline.cpp.

## double QwtSpline::boundaryValue (BoundaryPosition position) const¶

**Returns**

**Parameters**

*position*At the beginning or the end of the spline

**See also**

**setBoundaryValue()**,

**boundaryCondition()**

Definition at line 682 of file qwt_spline.cpp.

## uint QwtSpline::locality () const [virtual]¶

The locality of an spline interpolation identifies how many adjacent polynomials are affected, when changing the position of one point.

A locality of 'n' means, that changing the coordinates of a point has an effect on 'n' leading and 'n' following polynomials. Those polynomials can be calculated from a local subpolygon.

A value of 0 means, that the interpolation is not local and any modification of the polygon requires to recalculate all polynomials ( f.e cubic splines ).

**Returns**

Reimplemented in **QwtSplinePleasing**, **QwtSplineLocal**,
**QwtSplineCubic**, and **QwtSplineBasis**.

Definition at line 564 of file qwt_spline.cpp.

## QPainterPath QwtSpline::painterPath (const QPolygonF & points) const [pure virtual]¶

Approximates a polygon piecewise with cubic Bezier curves and returns them as QPainterPath.

**Parameters**

*points*Control points

**Returns**

**See also**

**polygon()**,

**QwtBezier**

Implemented in **QwtSplinePleasing**, **QwtSplineLocal**,
**QwtSplineCubic**, **QwtSplineBasis**, **QwtSplineC2**,
**QwtSplineC1**, and **QwtSplineInterpolating**.

## const QwtSplineParametrization * QwtSpline::parametrization () const¶

**Returns**

**See also**

**setParametrization()**

Definition at line 605 of file qwt_spline.cpp.

## QPolygonF QwtSpline::polygon (const QPolygonF & points, double tolerance) const [virtual]¶

Interpolate a curve by a polygon. Interpolates a polygon piecewise with Bezier curves interpolating them in a 2nd pass by polygons.

The interpolation is based on 'Piecewise Linear Approximation of Bézier Curves' by Roger Willcocks ( http://www.rops.org )

**Parameters**

*points*Control points

*tolerance*Maximum for the accepted error of the approximation

**Returns**

**See also**

**QwtBezier**

Reimplemented in **QwtSplineInterpolating**.

Definition at line 496 of file qwt_spline.cpp.

## void QwtSpline::setBoundaryCondition (BoundaryPosition position, int condition)¶

Define the condition for an endpoint of the spline.

**Parameters**

*position*At the beginning or the end of the spline

*condition*Condition

**See also**

**BoundaryCondition**,

**QwtSplineC2::BoundaryCondition**,

**boundaryCondition()**

Definition at line 639 of file qwt_spline.cpp.

## void QwtSpline::setBoundaryConditions (int condition, double valueBegin = 0.0, double valueEnd = 0.0)¶

Define the condition at the endpoints of a spline.

**Parameters**

*condition*Condition

*valueBegin*Used for the condition at the beginning of te spline

*valueEnd*Used for the condition at the end of te spline

**See also**

**BoundaryCondition**,

**QwtSplineC2::BoundaryCondition**, testBoundaryCondition(),

**setBoundaryValue()**

Definition at line 700 of file qwt_spline.cpp.

## void QwtSpline::setBoundaryType (BoundaryType boundaryType)¶

Define the boundary type for the endpoints of the approximating spline.

**Parameters**

*boundaryType*Boundary type

**See also**

**boundaryType()**

Definition at line 617 of file qwt_spline.cpp.

## void QwtSpline::setBoundaryValue (BoundaryPosition position, double value)¶

Define the boundary value. The boundary value is an parameter used in combination with the boundary condition. Its meaning depends on the condition.

**Parameters**

*position*At the beginning or the end of the spline

*value*Value used for the condition at the end point

**See also**

**boundaryValue()**,

**setBoundaryCondition()**

Definition at line 670 of file qwt_spline.cpp.

## void QwtSpline::setParametrization (int type)¶

Define the parametrization for a parametric spline approximation The default setting is a chordal parametrization.

**Parameters**

*type*Type of parametrization, usually one of

**QwtSplineParametrization::Type**

**See also**

**parametrization()**

Definition at line 576 of file qwt_spline.cpp.

## void QwtSpline::setParametrization (QwtSplineParametrization * parametrization)¶

Define the parametrization for a parametric spline approximation The default setting is a chordal parametrization.

**Parameters**

*parametrization*Parametrization

**See also**

**parametrization()**

Definition at line 592 of file qwt_spline.cpp.

# Author¶

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Sun Jul 18 2021 | Version 6.2.0 |