Different Units for a Scale?

[HappyCoder]

Hi,

actually my measurement values are a pair of time and pressure.
The pressure value is stored in [mbar].

What is the best way in Qwt to change the unit eg. [Torr] or [Pa] and other.

It it necessary to recalculate all values of a curve ( which is not good) or
is it possible to change the axis only?

Stefan

[Uwe]

You could derive from QwtSeriesData<QPointF>. Store the samples as they are and do the translation in QwtSeriesData<QPointF>::sample() and QwtSeriesData<QPointF>::boundingRect().

Uwe

[HappyCoder]

Hello Uwe,

just an idea, but can this be done also using QwtTransform if i add a new one like this (not tried):

mbarToTorrTransform::mbarToTorrTransform():
    QwtTransform()
{
}
mbarToTorrTransform::~mbarToTorrTransform()
{
}
 
double mbarToTorrTransform::transform( double value ) const
{
    return value*0.75006;
}
double mbarToTorrTransform::invTransform( double value ) const
{
    return value/0.75006;
}

mbarToTorrTransform::mbarToTorrTransform():
    QwtTransform()
{
}
mbarToTorrTransform::~mbarToTorrTransform()
{
}

double mbarToTorrTransform::transform( double value ) const
{
    return value*0.75006;
}
double mbarToTorrTransform::invTransform( double value ) const
{
    return value/0.75006;
}

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Thx
Stefan

[HappyCoder]

With the grateful help of phenoboy and some modifications i was able to create a subclass of QwtSeriesData.
But now application crashes on close with this message in Debugger

can't find linker symbol for virtual table for `QwtSeriesStore<QPointF>' value
found `construction vtable for QwtSeriesStore<QPointF>-in-PlotCurve' instead

What is going wrong here? (clean Project, qmake, rebuild all done)

It looks like the app crahes here:

template <typename T>
QwtSeriesStore<T>::~QwtSeriesStore()
{
    delete d_series;    // CRASH
}

template <typename T>
QwtSeriesStore<T>::~QwtSeriesStore()
{
    delete d_series;    // CRASH
}

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Thx
Stefan

My code:

plotcurve.h

#include "qwt/subclass/seriesdata.h"
...
SeriesData curveData;

#include "qwt/subclass/seriesdata.h"
...
SeriesData curveData;

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plotcurve.cpp

void PlotCurve::newCurveData()
{
    if( isPointerValid() )
    {
        // with subclass from QwtSeriesData
        curveData.setMinYValue( d_data->pmdata.data()->valueMin );
        curveData.setMaxYValue( d_data->pmdata.data()->valueMax );
        curveData.setSamples(d_data->pmdata.data()->timestamps,
                             d_data->pmdata.data()->values);
        curveData.setFactorY( d_data->unitPressureFactor );
 
        setSamples( &curveData );
}

void PlotCurve::newCurveData()
{
    if( isPointerValid() )
    {
        // with subclass from QwtSeriesData
        curveData.setMinYValue( d_data->pmdata.data()->valueMin );
        curveData.setMaxYValue( d_data->pmdata.data()->valueMax );
        curveData.setSamples(d_data->pmdata.data()->timestamps,
                             d_data->pmdata.data()->values);
        curveData.setFactorY( d_data->unitPressureFactor );

        setSamples( &curveData );
}

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seriesdata.h

#include "qwt_series_data.h"
#include <QObject>
 
class SeriesData : public QwtSeriesData<QPointF>
{
public:
    SeriesData();
 
    virtual QPointF sample( size_t index ) const;
    virtual size_t size() const;
    virtual QRectF boundingRect() const;
 
    double getFactorY() const;
    void setFactorY(const double &value);
 
    void setMaxYValue(const double &value);
    void setMinYValue(const double &value);
 
    void clear();
 
    void setSamples( const QVector<double> &xData, const QVector<double> &yData );
    QVector<double> &pointsX();
    QVector<double> &pointsY();
    QRectF _boundingRect;
 
protected:
    QVector<double> points_x;
    QVector<double> points_y;
    double factorY;
    double maxYValue;
    double minYValue;
};

#include "qwt_series_data.h"
#include <QObject>

class SeriesData : public QwtSeriesData<QPointF>
{
public:
    SeriesData();

    virtual QPointF sample( size_t index ) const;
    virtual size_t size() const;
    virtual QRectF boundingRect() const;

    double getFactorY() const;
    void setFactorY(const double &value);

    void setMaxYValue(const double &value);
    void setMinYValue(const double &value);

    void clear();

    void setSamples( const QVector<double> &xData, const QVector<double> &yData );
    QVector<double> &pointsX();
    QVector<double> &pointsY();
    QRectF _boundingRect;

protected:
    QVector<double> points_x;
    QVector<double> points_y;
    double factorY;
    double maxYValue;
    double minYValue;
};

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#include "seriesdata.h"
 
#include "qwt_series_data.h"
 
SeriesData::SeriesData()
{
    qDebug() << Q_FUNC_INFO;
 
    factorY = 1;
    points_x.reserve(1000);
    points_y.reserve(1000);
}
 
QPointF SeriesData::sample(size_t index) const
{
    QPointF p(points_x.value(index), points_y.value(index));
    p.setY(factorY*p.y());
    return p;
}
 
size_t SeriesData::size() const
{
    return points_x.size();
}
 
QRectF SeriesData::boundingRect() const
{
    return _boundingRect;
}
 
QVector<double> &SeriesData::pointsX()
{
    return points_x;
}
 
QVector<double> &SeriesData::pointsY()
{
    return points_y;
}
 
double SeriesData::getFactorY() const
{
    return factorY;
}
 
void SeriesData::setFactorY(const double &value)
{
    factorY = value;
}
 
void SeriesData::setMaxYValue(const double &value)
{
    maxYValue = value;
}
 
void SeriesData::setMinYValue(const double &value)
{
    minYValue = value;
}
 
void SeriesData::clear()
{
    points_x.clear();
    points_y.clear();
}
 
void SeriesData::setSamples(const QVector<double> &xData, const QVector<double> &yData)
{
    points_x = xData;
    points_y = yData;
 
    _boundingRect.setLeft( (qreal)(xData.first()) );
    _boundingRect.setRight( (qreal)(xData.last()) );
    _boundingRect.setTop( maxYValue );
    _boundingRect.setBottom( minYValue );
}

#include "seriesdata.h"

#include "qwt_series_data.h"

SeriesData::SeriesData()
{
    qDebug() << Q_FUNC_INFO;

    factorY = 1;
    points_x.reserve(1000);
    points_y.reserve(1000);
}

QPointF SeriesData::sample(size_t index) const
{
    QPointF p(points_x.value(index), points_y.value(index));
    p.setY(factorY*p.y());
    return p;
}

size_t SeriesData::size() const
{
    return points_x.size();
}

QRectF SeriesData::boundingRect() const
{
    return _boundingRect;
}

QVector<double> &SeriesData::pointsX()
{
    return points_x;
}

QVector<double> &SeriesData::pointsY()
{
    return points_y;
}

double SeriesData::getFactorY() const
{
    return factorY;
}

void SeriesData::setFactorY(const double &value)
{
    factorY = value;
}

void SeriesData::setMaxYValue(const double &value)
{
    maxYValue = value;
}

void SeriesData::setMinYValue(const double &value)
{
    minYValue = value;
}

void SeriesData::clear()
{
    points_x.clear();
    points_y.clear();
}

void SeriesData::setSamples(const QVector<double> &xData, const QVector<double> &yData)
{
    points_x = xData;
    points_y = yData;

    _boundingRect.setLeft( (qreal)(xData.first()) );
    _boundingRect.setRight( (qreal)(xData.last()) );
    _boundingRect.setTop( maxYValue );
    _boundingRect.setBottom( minYValue );
}

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