Implimentation advice for a large data plotting application.

[Uwe]

If I understand correctly then, I need to add a type of filtering class to my data class to return effectively a lower resolution version of the data it internally stores to the QwtPlot (or QwtPlotCurve not sure which)?

Inside of your data object. I recommend to connect something to the QwtScaleWidget::scaleDivChanged() signals to activate the best resolution for the current scale ranges.

You suggested I looked at the QwtWeedingCurveFitter, however I don't seem to be able to find this, where should I be looking?

qwt_curve_fitter.[h|cpp] - didn't you write, that you are on trunk ?

I was also wondering if there is a description somewhere as to how the QwtPlotZoomer works with a QwtPlot and its associated QwtPlotCurve classes (and ultimately my data class derived from QwtSeriesData).

The zoomer manipulates the scales - your curves and your data object are completely unrelated. Note that the plot has current scale ranges, but the zoom stack is an internal thing of the zoomer. For rendering the content of the plot canvas it is unimportant if the scales are the result of a zoom operation or not.

... however I was a little surprised when the sample index that my data class was asked for always ranged over the entire data set. I had expected the zoom area to have been the bound on this.

In general the index of a point has nothing to do with its coordinates ( start the realtime example, zoom in and you will understand immediately ) !

I guess in your specific situation the values are ordered, what could be used to optimize painting but using specific characteristics of a series can only be implemented, where these are known: your data object.

Why is this not the first and last point identified from the zoomer?

Again, there are not first and last points according to coordinates. But even coordinates, that are outside of the scale ranges might be important: f.e. in case of QwtPlotCurve::Lines the connecting line might be intersecting the visible area.

Is it the QwtPlot that discards data points which fall outsize of its zoom range

QwtPlotCurve does some optimizations like polygon clipping or discarding points depending on the type of visualization. But it can't do it without knowing the points.

Uwe