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#include <qwt_math.h>
#include <qwt_scale_engine.h>
#include <qwt_symbol.h>
#include <qwt_plot_grid.h>
#include <qwt_plot_marker.h>
#include <qwt_plot_curve.h>
#include <qwt_legend.h>
#include <qwt_text.h>
#include <qwt_plot_canvas.h>
#include <qmath.h>
#include "complexnumber.h"
#include "plot.h"
#if QT_VERSION < 0x040601
#define qExp(x) ::exp(x)
#define qAtan2(y, x) ::atan2(y, x)
#endif
static void logSpace( double *array, int size, double xmin, double xmax )
{
if ( ( xmin <= 0.0 ) || ( xmax <= 0.0 ) || ( size <= 0 ) )
return;
const int imax = size - 1;
array[0] = xmin;
array[imax] = xmax;
const double lxmin = log( xmin );
const double lxmax = log( xmax );
const double lstep = ( lxmax - lxmin ) / double( imax );
for ( int i = 1; i < imax; i++ )
array[i] = qExp( lxmin + double( i ) * lstep );
}
Plot::Plot( QWidget *parent ):
QwtPlot( parent )
{
setAutoReplot( false );
setTitle( "Frequency Response of a Second-Order System" );
QwtPlotCanvas *canvas = new QwtPlotCanvas();
canvas->setBorderRadius( 10 );
setCanvas( canvas );
setCanvasBackground( QColor( "MidnightBlue" ) );
// legend
QwtLegend *legend = new QwtLegend;
insertLegend( legend, QwtPlot::BottomLegend );
// grid
QwtPlotGrid *grid = new QwtPlotGrid;
grid->enableXMin( true );
grid->setMajorPen( Qt::white, 0, Qt::DotLine );
grid->setMinorPen( Qt::gray, 0 , Qt::DotLine );
grid->attach( this );
// axes
enableAxis( QwtPlot::yRight );
setAxisTitle( QwtPlot::xBottom, "Normalized Frequency" );
setAxisTitle( QwtPlot::yLeft, "Amplitude [dB]" );
setAxisTitle( QwtPlot::yRight, "Phase [deg]" );
setAxisMaxMajor( QwtPlot::xBottom, 6 );
setAxisMaxMinor( QwtPlot::xBottom, 9 );
setAxisScaleEngine( QwtPlot::xBottom, new QwtLogScaleEngine );
// curves
d_curve1 = new QwtPlotCurve( "Amplitude" );
d_curve1->setRenderHint( QwtPlotItem::RenderAntialiased );
d_curve1->setPen( Qt::yellow );
d_curve1->setLegendAttribute( QwtPlotCurve::LegendShowLine );
d_curve1->setYAxis( QwtPlot::yLeft );
d_curve1->attach( this );
d_curve2 = new QwtPlotCurve( "Phase" );
d_curve2->setRenderHint( QwtPlotItem::RenderAntialiased );
d_curve2->setPen( Qt::cyan );
d_curve2->setLegendAttribute( QwtPlotCurve::LegendShowLine );
d_curve2->setYAxis( QwtPlot::yRight );
d_curve2->attach( this );
// marker
d_marker1 = new QwtPlotMarker();
d_marker1->setValue( 0.0, 0.0 );
d_marker1->setLineStyle( QwtPlotMarker::VLine );
d_marker1->setLabelAlignment( Qt::AlignRight | Qt::AlignBottom );
d_marker1->setLinePen( Qt::green, 0, Qt::DashDotLine );
d_marker1->attach( this );
d_marker2 = new QwtPlotMarker();
d_marker2->setLineStyle( QwtPlotMarker::HLine );
d_marker2->setLabelAlignment( Qt::AlignRight | Qt::AlignBottom );
d_marker2->setLinePen( QColor( 200, 150, 0 ), 0, Qt::DashDotLine );
d_marker2->setSymbol( new QwtSymbol( QwtSymbol::Diamond,
QColor( Qt::yellow ), QColor( Qt::green ), QSize( 8, 8 ) ) );
d_marker2->attach( this );
setDamp( 0.0 );
setAutoReplot( true );
}
void Plot::showData( const double *frequency, const double *amplitude,
const double *phase, int count )
{
d_curve1->setSamples( frequency, amplitude, count );
d_curve2->setSamples( frequency, phase, count );
}
void Plot::showPeak( double freq, double amplitude )
{
QString label;
label.sprintf( "Peak: %.3g dB", amplitude );
QwtText text( label );
text.setFont( QFont( "Helvetica", 10, QFont::Bold ) );
text.setColor( QColor( 200, 150, 0 ) );
d_marker2->setValue( freq, amplitude );
d_marker2->setLabel( text );
}
void Plot::show3dB( double freq )
{
QString label;
label.sprintf( "-3 dB at f = %.3g", freq );
QwtText text( label );
text.setFont( QFont( "Helvetica", 10, QFont::Bold ) );
text.setColor( Qt::green );
d_marker1->setValue( freq, 0.0 );
d_marker1->setLabel( text );
}
//
// re-calculate frequency response
//
void Plot::setDamp( double damping )
{
const bool doReplot = autoReplot();
setAutoReplot( false );
const int ArraySize = 200;
double frequency[ArraySize];
double amplitude[ArraySize];
double phase[ArraySize];
// build frequency vector with logarithmic division
logSpace( frequency, ArraySize, 0.01, 100 );
int i3 = 1;
double fmax = 1;
double amax = -1000.0;
for ( int i = 0; i < ArraySize; i++ )
{
double f = frequency[i];
const ComplexNumber g =
ComplexNumber( 1.0 ) / ComplexNumber( 1.0 - f * f, 2.0 * damping * f );
amplitude[i] = 20.0 * log10( qSqrt( g.real() * g.real() + g.imag() * g.imag() ) );
phase[i] = qAtan2( g.imag(), g.real() ) * ( 180.0 / M_PI );
if ( ( i3 <= 1 ) && ( amplitude[i] < -3.0 ) )
i3 = i;
if ( amplitude[i] > amax )
{
amax = amplitude[i];
fmax = frequency[i];
}
}
double f3 = frequency[i3] - ( frequency[i3] - frequency[i3 - 1] )
/ ( amplitude[i3] - amplitude[i3 -1] ) * ( amplitude[i3] + 3 );
showPeak( fmax, amax );
show3dB( f3 );
showData( frequency, amplitude, phase, ArraySize );
setAutoReplot( doReplot );
replot();
}
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