QwtSplineParametrization - Man Page

Curve parametrization used for a spline interpolation.

Synopsis

#include <qwt_spline_parametrization.h>

Public Types

enum Type { ParameterX, ParameterY, ParameterUniform, ParameterChordal, ParameterCentripetal, ParameterManhattan }
Parametrization type.

QwtSplineParametrization (int type)
virtual ~QwtSplineParametrization ()
Destructor.
int type () const
virtual double valueIncrement (const QPointF &, const QPointF &) const
Calculate the parameter value increment for 2 points.

Static Public Member Functions

static double valueIncrementX (const QPointF &, const QPointF &)
Calculate the ParameterX value increment for 2 points.
static double valueIncrementY (const QPointF &, const QPointF &)
Calculate the ParameterY value increment for 2 points.
static double valueIncrementUniform (const QPointF &, const QPointF &)
Calculate the ParameterUniform value increment.
static double valueIncrementChordal (const QPointF &, const QPointF &)
Calculate the ParameterChordal value increment for 2 points.
static double valueIncrementCentripetal (const QPointF &, const QPointF &)
Calculate the ParameterCentripetal value increment for 2 points.
static double valueIncrementManhattan (const QPointF &, const QPointF &)
Calculate the ParameterManhattan value increment for 2 points.

Detailed Description

Curve parametrization used for a spline interpolation.

Parametrization is the process of finding a parameter value for each curve point - usually related to some physical quantity ( distance, time ... ).

Often accumulating the curve length is the intended way of parametrization, but as the interpolated curve is not known in advance an approximation needs to be used.

The values are calculated by cumulating increments, that are provided by QwtSplineParametrization. As the curve parameters need to be montonically increasing, each increment need to be positive.

t[0] = 0;
t[i] = t[i-1] + valueIncrement( point[i-1], p[i] );

QwtSplineParametrization provides the most common used type of parametrizations and offers an interface to inject custom implementations.

Note: The most relevant types of parametrization are trying to provide an approximation of the curve length.
See also: QwtSpline::setParametrization()

Definition at line 44 of file qwt_spline_parametrization.h.

Member Enumeration Documentation

enum QwtSplineParametrization::Type

Parametrization type.

Enumerator

ParameterX: No parametrization: t[i] = x[i]
See also: valueIncrementX()
ParameterY: No parametrization: t[i] = y[i]
See also: valueIncrementY()
ParameterUniform: Uniform parametrization: t[i] = i;

A very fast parametrization, with good results, when the geometry of the control points is somehow 'equidistant'. F.e. when recording the position of a body, that is moving with constant speed every n seconds.

See also: valueIncrementUniform()
ParameterChordal: Parametrization using the chordal length between two control points

The chordal length is the most commonly used approximation for the curve length.