Drawing Rect on QwtPlot

[baray98]

I am planning to overlay some boxes (rects) on top of my spectrogram but i am not sure how to go about this.

background:

these boxes can be up to millions ,information is from a database so i am expecting lots.

I dont think all of them will be shown in one time, its just too much information to handle for the user - say if valid x is from 0 to 1000000 , i will only give my user maximum of 200 units x at a time , and they can scroll left and right to navigate from 0 - 1000000. but still i should be prepared to handle more than 100 boxes.

My plans:

a) I would sublass QwtPlotItem which will represent a single rect.plot will have lots of items to draw i am not sure if this is efficient;
b) I would give a plotCurve a Rect Data (4 points) which represent a rect. This is worse than option a i think.

your thoughts? your opinion is highly appreciated

baray98

[Uwe]

With the version of SVN trunk you could use a QwtPlotShapeItem - with Qwt 6.0 you can use the RectItem from the navigation example.
Using curves for displaying rectangles is no good idea - as long as its size depends on plot coordinates ( otherwise it could be a curve symbol ).

Using one item for each rectangle of course has a lot overhead compared with an implementation where you have one item for all rectangles. But this depends on details I don't know.

Uwe

[esutton]

I am just getting started with Qwt. In case it may be relevant to your application, the Qwt example cpuplot draws a pie chart overlay on the graph.

Or maybe a hover over and display tool-tip approach might be less cluttered? The user could hover over a peak and tool tip could display relevant nformation?

-Ed

[Uwe]

The user could hover over a peak and tool tip could display relevant information?

This is usually done with a QwtPlotPicker - you find many threads about this topic in this forum. Note that QwtText can have a background with a frame ( = rectangle ) around the tracker text.

In opposite to a tracker you can use a marker if you want to have something persistant ( f.e when it should be part of a PDF you want to generate ).

Uwe

[esutton]

This is usually done with a QwtPlotPicker
Uwe

Good tip thank you!