Time/Date Axis

[dinojerm]

I wrote code for this stuff, based on the provided Qwt examples.
For the time/date axis, the following simple class was used (it assumes the time is stored in the time_t form):

class StockTimeScaleDraw: public QwtScaleDraw
{
public:
	StockTimeScaleDraw(QString fmt) : format(fmt) { }
 
    virtual QwtText label(double v) const
    {
		QDateTime t = QDateTime::fromTime_t((int)v);
		return t.toString(format);
    }
private:
	const QString format;
}

class StockTimeScaleDraw: public QwtScaleDraw
{
public:
	StockTimeScaleDraw(QString fmt) : format(fmt) { }

    virtual QwtText label(double v) const
    {
		QDateTime t = QDateTime::fromTime_t((int)v);
		return t.toString(format);
    }
private:
	const QString format;
}

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The attached program contains a plot item to draw candlesticks based on OHLC data. This example generates random data each second, aggregating and creating bars every 10 seconds. Another feature that might be useful is the ability to adjust the scale by clicking and dragging the axes.
Hopefully some of this will be helpful to others.

[philwinder]

Thanks for the code post. Here is an much more simple example of a plot using a QDateTime base.

[drizzt]

i want to have a timescale with millisecond accuracy, but i don't really know how to do that.
All examples only have second accuracy and always use QDateTime::fromTime_t(int v) or something else.

Has somebody experiences with that and can give me a tip how to solve that problem?

thx

[Lupus]

Hej drizzt.
My idea would be to create a similar type to time_t where you count milliseconds from some start date.
The easiest thing would be to use QDateTime::toTime_t of your start date and multiply it to get your milliseconds and add as many milliseconds as needed for the datapoint
Then you could call

QDateTime t = QDateTime::addMSecs((qint64)v);
return t.toString("yyyy-MM-dd HH:mm:ss:zzz");

in the label function from dinojerm.

Just take care of the really big number which is lager than an interger, so use qint64.
I have NOT tested this, it ist just a suggestion.

[techr]

Hi Phil Winder,
is it possible to get the datetime.zip? looks like the above link does not contain all the files...after i download, i could not unzip it...

Thanks in advance

[Patrik]

I'm very interested in something similar to this. Basically I need only dates as X axis. Do you thing this snippet is correct?

QwtPlot *plt = ui->qwtPlot;
plt->setAxisScaleDraw(QwtPlot::xBottom, new TimeScaleDraw("dd/M/yy"));
QDate date = getDateFromSomewhere();
QDateTime tm(date);
xData.append(tm.toTime_t());
yData.append(someData());

[FelixB]

I'm very interested in something similar to this. Basically I need only dates as X axis. Do you thing this snippet is correct?

why don't you try it by yourself?

[falconium]

Hi Philminder, I tried your example under 6.00-rc5, and it fails at:

..\datetime\mainwindow.cpp: In constructor 'MainWindow::MainWindow(QWidget*)':
..\datetime\mainwindow.cpp:40: error: no matching function for call to 'QwtPlotCurve::setData(double*, double*, int)'
..\libraries\qwt/qwt_plot_seriesitem.h:146: note: candidates are: void QwtPlotSeriesItem<T>::setData(QwtSeriesData<T>*) [with T = QPointF]

It looks like setData arguments have changed...

[corrado1972]

please download latest Qwt (6.0) and recompile: it should works.

[TorAn]

corrado1972 -
I downloaded datetime.zip and curve->setData(&xData[0], &yData[0], xData.size()); (mainwindow.cpp line40) does not compile with Qwt 6.0.0.

setData should be replaced with setRawSamples

[corrado1972]

TorAn excuse me but I understood that the problem was referred to the examples included in Qwt release.
My advice is to discard the datetime.zip and look in the examples, friedberg and cpuplot: there is all the necessary to get datetime axis.
bye