Quote Originally Posted by bwnicewo View Post
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.
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