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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 "cplx.h"
#include "bode_plot.h"
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] = exp(lxmin + double(i) * lstep);
}
BodePlot::BodePlot(QWidget *parent):
QwtPlot(parent)
{
setAutoReplot(false);
setTitle("Frequency Response of a Second-Order System");
setCanvasBackground(QColor(Qt::darkBlue));
// legend
QwtLegend *legend = new QwtLegend;
legend->setFrameStyle(QFrame::Box|QFrame::Sunken);
insertLegend(legend, QwtPlot::BottomLegend);
// grid
QwtPlotGrid *grid = new QwtPlotGrid;
grid->enableXMin(true);
grid->setMajPen(QPen(Qt::white, 0, Qt::DotLine));
grid->setMinPen(QPen(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, 10);
setAxisScaleEngine(QwtPlot::xBottom, new QwtLog10ScaleEngine);
// curves
d_crv1 = new QwtPlotCurve("Amplitude");
#if QT_VERSION >= 0x040000
d_crv1->setRenderHint(QwtPlotItem::RenderAntialiased);
#endif
d_crv1->setPen(QPen(Qt::yellow));
d_crv1->setYAxis(QwtPlot::yLeft);
d_crv1->attach(this);
d_crv2 = new QwtPlotCurve("Phase");
#if QT_VERSION >= 0x040000
d_crv2->setRenderHint(QwtPlotItem::RenderAntialiased);
#endif
d_crv2->setPen(QPen(Qt::cyan));
d_crv2->setYAxis(QwtPlot::yRight);
d_crv2->attach(this);
// marker
d_mrk1 = new QwtPlotMarker();
d_mrk1->setValue(0.0, 0.0);
d_mrk1->setLineStyle(QwtPlotMarker::VLine);
d_mrk1->setLabelAlignment(Qt::AlignRight | Qt::AlignBottom);
d_mrk1->setLinePen(QPen(Qt::green, 0, Qt::DashDotLine));
d_mrk1->attach(this);
d_mrk2 = new QwtPlotMarker();
d_mrk2->setLineStyle(QwtPlotMarker::HLine);
d_mrk2->setLabelAlignment(Qt::AlignRight | Qt::AlignBottom);
d_mrk2->setLinePen(QPen(QColor(200,150,0), 0, Qt::DashDotLine));
d_mrk2->setSymbol( QwtSymbol(QwtSymbol::Diamond,
QColor(Qt::yellow), QColor(Qt::green), QSize(7,7)));
d_mrk2->attach(this);
setDamp(0.0);
setAutoReplot(true);
}
void BodePlot::showData(double *frequency, double *amplitude,
double *phase, int count)
{
d_crv1->setData(frequency, amplitude, count);
d_crv2->setData(frequency, phase, count);
}
void BodePlot::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_mrk2->setValue(freq, amplitude);
d_mrk2->setLabel(text);
}
void BodePlot::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_mrk1->setValue(freq, 0.0);
d_mrk1->setLabel(text);
}
//
// re-calculate frequency response
//
void BodePlot::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];
cplx g = cplx(1.0) / cplx(1.0 - f * f, 2.0 * damping * f);
amplitude[i] = 20.0 * log10(sqrt( g.real()*g.real() + g.imag()*g.imag()));
phase[i] = atan2(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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