# QwtSplineInterpolating - Man Page

Base class for a spline interpolation.

## Synopsis

`#include <qwt_spline.h>`

Inherits **QwtSpline**.

Inherited by **QwtSplineG1**.

### Public Member Functions

**QwtSplineInterpolating** ()

Constructor.

virtual **~QwtSplineInterpolating** ()

Destructor.

virtual QPolygonF **equidistantPolygon** (const QPolygonF &, double distance, bool withNodes) const

Find an interpolated polygon with 'equidistant' points.

virtual QPolygonF **polygon** (const QPolygonF &, double tolerance) const override

Interpolate a curve by a polygon.

virtual QPainterPath **painterPath** (const QPolygonF &) const override

Interpolate a curve with Bezier curves.

virtual **QVector**< QLineF > **bezierControlLines** (const QPolygonF &) const =0

Interpolate a curve with Bezier curves.

### Additional Inherited Members

## Detailed Description

Base class for a spline interpolation.

Spline interpolation is the process of interpolating a set of points piecewise with polynomials. The initial set of points is preserved.

Definition at line 193 of file qwt_spline.h.

## Member Function Documentation

### QVector< QLineF > QwtSplineInterpolating::bezierControlLines (const QPolygonF & points) const [pure virtual]

Interpolate a curve with Bezier curves. Interpolates a polygon piecewise with cubic Bezier curves and returns the 2 control points of each curve as QLineF.

**Parameters***points*Control points**Returns**Control points of the interpolating Bezier curves

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

### QPolygonF QwtSplineInterpolating::equidistantPolygon (const QPolygonF & points, double distance, bool withNodes) const [virtual]

Find an interpolated polygon with 'equidistant' points. When withNodes is disabled all points of the resulting polygon will be equidistant according to the parametrization.

When withNodes is enabled the resulting polygon will also include the control points and the interpolated points are always aligned to the control point before ( points[i] + i * distance ).

The implementation calculates bezier curves first and calculates the interpolated points in a second run.

**Parameters***points*Control nodes of the spline*distance*Distance between 2 points according to the parametrization*withNodes*When true, also add the control nodes ( even if not being equidistant )**Returns**Interpolating polygon

**See also****bezierControlLines()**

Reimplemented in **QwtSplineC2**, and **QwtSplineC1**.

Definition at line 863 of file qwt_spline.cpp.

### QPainterPath QwtSplineInterpolating::painterPath (const QPolygonF & points) const [override], [virtual]

Interpolate a curve with Bezier curves. Interpolates a polygon piecewise with cubic Bezier curves and returns them as QPainterPath.

The implementation calculates the Bezier control lines first and converts them into painter path elements in an additional loop.

**Parameters***points*Control points**Returns**Painter path, that can be rendered by QPainter

**Note**Derived spline classes might overload

**painterPath()**to avoid the extra loops for converting results into a QPainterPath**See also****bezierControlLines()**

Implements **QwtSpline**.

Reimplemented in **QwtSplinePleasing**, **QwtSplineLocal**, **QwtSplineCubic**, **QwtSplineC2**, and **QwtSplineC1**.

Definition at line 748 of file qwt_spline.cpp.

### QPolygonF QwtSplineInterpolating::polygon (const QPolygonF & points, double tolerance) const [override], [virtual]

Interpolate a curve by a polygon. Interpolates a polygon piecewise with Bezier curves approximating them by polygons.

The approximation 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**polygon approximating the interpolating polynomials

**See also****bezierControlLines()**, QwtSplineBezier::toPolygon()

Reimplemented from **QwtSpline**.

Definition at line 805 of file qwt_spline.cpp.

## Author

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