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examples/bode/Plot.cpp
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197
examples/bode/Plot.cpp
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/*****************************************************************************
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* Qwt Examples
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* Copyright (C) 1997 Josef Wilgen
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* Copyright (C) 2002 Uwe Rathmann
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the Qwt License, Version 1.0
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*****************************************************************************/
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#include "Plot.h"
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#include "ComplexNumber.h"
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#include <QwtMath>
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#include <QwtScaleEngine>
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#include <QwtSymbol>
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#include <QwtPlotGrid>
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#include <QwtPlotMarker>
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#include <QwtPlotCurve>
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#include <QwtLegend>
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#include <QwtText>
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#include <QwtPlotCanvas>
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static void logSpace( double* array, int size, double xmin, double xmax )
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{
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if ( ( xmin <= 0.0 ) || ( xmax <= 0.0 ) || ( size <= 0 ) )
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return;
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const int imax = size - 1;
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array[0] = xmin;
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array[imax] = xmax;
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const double lxmin = log( xmin );
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const double lxmax = log( xmax );
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const double lstep = ( lxmax - lxmin ) / double( imax );
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for ( int i = 1; i < imax; i++ )
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array[i] = std::exp( lxmin + double( i ) * lstep );
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}
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Plot::Plot( QWidget* parent )
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: QwtPlot( parent )
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{
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setAutoReplot( false );
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setTitle( "Frequency Response of a Second-Order System" );
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QwtPlotCanvas* canvas = new QwtPlotCanvas();
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canvas->setBorderRadius( 10 );
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setCanvas( canvas );
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setCanvasBackground( QColor( "MidnightBlue" ) );
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// legend
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QwtLegend* legend = new QwtLegend;
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insertLegend( legend, QwtPlot::BottomLegend );
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// grid
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QwtPlotGrid* grid = new QwtPlotGrid;
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grid->enableXMin( true );
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grid->setMajorPen( Qt::white, 0, Qt::DotLine );
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grid->setMinorPen( Qt::gray, 0, Qt::DotLine );
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grid->attach( this );
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// axes
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setAxisVisible( QwtAxis::YRight );
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setAxisTitle( QwtAxis::XBottom, "Normalized Frequency" );
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setAxisTitle( QwtAxis::YLeft, "Amplitude [dB]" );
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setAxisTitle( QwtAxis::YRight, "Phase [deg]" );
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setAxisMaxMajor( QwtAxis::XBottom, 6 );
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setAxisMaxMinor( QwtAxis::XBottom, 9 );
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setAxisScaleEngine( QwtAxis::XBottom, new QwtLogScaleEngine );
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// curves
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m_curve1 = new QwtPlotCurve( "Amplitude" );
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m_curve1->setRenderHint( QwtPlotItem::RenderAntialiased );
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m_curve1->setPen( Qt::yellow );
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m_curve1->setLegendAttribute( QwtPlotCurve::LegendShowLine );
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m_curve1->setYAxis( QwtAxis::YLeft );
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m_curve1->attach( this );
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m_curve2 = new QwtPlotCurve( "Phase" );
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m_curve2->setRenderHint( QwtPlotItem::RenderAntialiased );
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m_curve2->setPen( Qt::cyan );
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m_curve2->setLegendAttribute( QwtPlotCurve::LegendShowLine );
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m_curve2->setYAxis( QwtAxis::YRight );
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m_curve2->attach( this );
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// marker
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m_marker1 = new QwtPlotMarker();
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m_marker1->setValue( 0.0, 0.0 );
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m_marker1->setLineStyle( QwtPlotMarker::VLine );
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m_marker1->setLabelAlignment( Qt::AlignRight | Qt::AlignBottom );
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m_marker1->setLinePen( Qt::green, 0, Qt::DashDotLine );
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m_marker1->attach( this );
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m_marker2 = new QwtPlotMarker();
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m_marker2->setLineStyle( QwtPlotMarker::HLine );
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m_marker2->setLabelAlignment( Qt::AlignRight | Qt::AlignBottom );
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m_marker2->setLinePen( QColor( 200, 150, 0 ), 0, Qt::DashDotLine );
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m_marker2->setSymbol( new QwtSymbol( QwtSymbol::Diamond,
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QColor( Qt::yellow ), QColor( Qt::green ), QSize( 8, 8 ) ) );
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m_marker2->attach( this );
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setDamp( 0.0 );
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setAutoReplot( true );
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}
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void Plot::showData( const double* frequency, const double* amplitude,
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const double* phase, int count )
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{
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m_curve1->setSamples( frequency, amplitude, count );
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m_curve2->setSamples( frequency, phase, count );
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}
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void Plot::showPeak( double freq, double amplitude )
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{
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QString label( "Peak: " );
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label += QString::number( amplitude, 'g', 3 );
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label += " dB";
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QwtText text( label );
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text.setFont( QFont( "Helvetica", 10, QFont::Bold ) );
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text.setColor( QColor( 200, 150, 0 ) );
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m_marker2->setValue( freq, amplitude );
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m_marker2->setLabel( text );
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}
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void Plot::show3dB( double freq )
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{
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QString label( "-3 dB at f = " );
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label += QString::number( freq, 'g', 3 );
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QwtText text( label );
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text.setFont( QFont( "Helvetica", 10, QFont::Bold ) );
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text.setColor( Qt::green );
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m_marker1->setValue( freq, 0.0 );
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m_marker1->setLabel( text );
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}
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//
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// re-calculate frequency response
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//
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void Plot::setDamp( double damping )
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{
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const bool doReplot = autoReplot();
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setAutoReplot( false );
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const int ArraySize = 200;
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double frequency[ArraySize];
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double amplitude[ArraySize];
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double phase[ArraySize];
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// build frequency vector with logarithmic division
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logSpace( frequency, ArraySize, 0.01, 100 );
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int i3 = 1;
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double fmax = 1;
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double amax = -1000.0;
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for ( int i = 0; i < ArraySize; i++ )
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{
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double f = frequency[i];
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const ComplexNumber g =
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ComplexNumber( 1.0 ) / ComplexNumber( 1.0 - f * f, 2.0 * damping * f );
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amplitude[i] = 20.0 * log10( std::sqrt( g.real() * g.real() + g.imag() * g.imag() ) );
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phase[i] = std::atan2( g.imag(), g.real() ) * ( 180.0 / M_PI );
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if ( ( i3 <= 1 ) && ( amplitude[i] < -3.0 ) )
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i3 = i;
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if ( amplitude[i] > amax )
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{
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amax = amplitude[i];
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fmax = frequency[i];
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}
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}
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double f3 = frequency[i3] - ( frequency[i3] - frequency[i3 - 1] )
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/ ( amplitude[i3] - amplitude[i3 - 1] ) * ( amplitude[i3] + 3 );
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showPeak( fmax, amax );
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show3dB( f3 );
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showData( frequency, amplitude, phase, ArraySize );
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setAutoReplot( doReplot );
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replot();
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}
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#include "moc_Plot.cpp"
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