Phasor Plotting with QwtPolar (drawing rays on a polar coordinate grid)

I'm trying to draw rays on a phasor coordinate plane and I have no idea what function to use or any example code that I could follow, in the Qwt Polar Documentation I found a drawRays method but the arguments are way too confusing. I'm using a QwtPhasorGrid. Could someone who has done this before help me, preferably with code examples? Thanks!

Here's my code:
Attachment 7292

There is no QwtPhasorGrid and the code you have posted shows nothing - so what do you want to display how ?

Uwe

Well, I'm trying to draw rays on a polar coordinate plane, the code in my first post will display a polar coordinate grid but I don't know how to plot a ray from the origin given the degrees and magnitude of the line. I was kind of forced to use something that someone didn't finish and he is now gone.

Quote:

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Originally Posted by bwnicewo

Well, I'm trying to draw rays on a polar coordinate plane, the code in my first post will display a polar coordinate grid but I don't know how to plot a ray from the origin given the degrees and magnitude of the line.

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The grid lines are rendered according to the ticks of the scales. If you want to to modify the grid ( having lines at different angles ) you have to modify the scale for the azimuth ( QwtPolar::AxisAzimuth ) - or configure the autoscaler that is responsible for calculating this scale. Check the QwtPolarPlot::setAxisXY methods.

You can change the pen, that is used for drawing the grid lines by QwtPolarGrid::setMajorGridPen/setMinorGridPen - if this is what you mean by magnitude.

In general drawing something to a plot widget is done by configuring and attaching Qwt plot item - or implementing your own type of plot items.

Uwe

Yeah, I wanted to attach an item to the plot, but I'm worried that I'll have to impliment my own plot item for just drawing a simple line from the origin, I would think there should just be a function to draw a line like drawLine or something that takes the length of the line and angle of the line.

You can't simply draw to a widget - this is not how Qt works. On most platforms you can't event paint outside paint events at all. You also need to take care of the plot -> widget transformation, that is changing on different type of layout events or when zooming in/out. But having a class around a couple of lines of render code ( this is what your is plot item about) is nothing to be afraid of.

QwtPlotMarker has a mode for drawing such a line - but I simply forgot to add a similar feature to QwtPolarMarker.

Uwe

What I have now to post the data is this:

d_grid = new QwtPolarGrid();
d_grid->setPen(QPen(Qt::white));
for ( int scaleId = 0; scaleId < QwtPolar::ScaleCount; scaleId++ )
{
d_grid->showGrid(scaleId);
d_grid->showMinorGrid(scaleId);

QPen minorPen(Qt::gray);
#if 0
minorPen.setStyle(Qt::DotLine);
#endif
d_grid->setMinorGridPen(scaleId, minorPen);
}
d_grid->setAxisPen(QwtPolar::AxisAzimuth, QPen(Qt::black));

d_grid->showAxis(QwtPolar::AxisAzimuth, true);
d_grid->showAxis(QwtPolar::AxisLeft, false);
d_grid->showAxis(QwtPolar::AxisRight, false);
d_grid->showAxis(QwtPolar::AxisTop, false);
d_grid->showAxis(QwtPolar::AxisBottom, false);
d_grid->showGrid(QwtPolar::Azimuth, true);
d_grid->showGrid(QwtPolar::Radius, true);
d_grid->attach(this);

// curves
m_curve = new QwtPolarCurve();
m_curve->setPen(QPen(Qt::red));
m_curve->setData(SinData(0,10));
m_curve->setPen(QPen(Qt::red));
m_curve->attach(this);
replot();

SinData is a class to return a QwtData pointer to setData, the arguments are an angle offset and amplitude of the line respectively. I'm attaching it to a QwtPolarPlot, the problem is I'm not seeing anything on the grid.

This wasn't my code, someone else wrote it.

bwnicewo, You solved it?