[Solved]Unable to calculate proper intervals for time plot

[C403]

Hey,

I've got this plot with a custom canvas, curve, legend and plotpicker. Everything works great. I'm trying to add date/time support on the x axis. This plot receives real time data and replots as new values arrive, x axis is time. For testing purposes I am firing off a signal every 1000ms that adds a point with a random [0,120] value on the y axis and the current time on the x axis. For the plot I am assigning the following for the scales:

From the StockChart example:

class DateScaleDraw: public QwtDateScaleDraw
{
public:
    DateScaleDraw(Qt::TimeSpec timeSpec):
        QwtDateScaleDraw( timeSpec )
    {
        setDateFormat(QwtDate::Millisecond, "hh:mm:ss:zzz\nddd dd MMM");
        setDateFormat(QwtDate::Second, "HH:MM:ss\nddd dd MMM");
        setDateFormat(QwtDate::Minute, "HH:MM\nddd dd MMM");
        setDateFormat(QwtDate::Hour, "MM:MM\nddd dd MMM");
        setDateFormat(QwtDate::Day, "ddd dd MMM yyyy");
        setDateFormat(QwtDate::Week, "Www");
        setDateFormat(QwtDate::Month, "MMM yyyy");
        setDateFormat(QwtDate::Year, "yyyy");
    }
 
};

class DateScaleDraw: public QwtDateScaleDraw
{
public:
    DateScaleDraw(Qt::TimeSpec timeSpec):
        QwtDateScaleDraw( timeSpec )
    {
        setDateFormat(QwtDate::Millisecond, "hh:mm:ss:zzz\nddd dd MMM");
        setDateFormat(QwtDate::Second, "HH:MM:ss\nddd dd MMM");
        setDateFormat(QwtDate::Minute, "HH:MM\nddd dd MMM");
        setDateFormat(QwtDate::Hour, "MM:MM\nddd dd MMM");
        setDateFormat(QwtDate::Day, "ddd dd MMM yyyy");
        setDateFormat(QwtDate::Week, "Www");
        setDateFormat(QwtDate::Month, "MMM yyyy");
        setDateFormat(QwtDate::Year, "yyyy");
    }

};

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Now:

QwtDateScaleDraw *scaleDraw = new DateScaleDraw(Qt::UTC );
    QwtDateScaleEngine *scaleEngine = new QwtDateScaleEngine(Qt::UTC);
 
    setAxisScaleDraw( QwtPlot::xBottom, scaleDraw );
    setAxisScaleEngine( QwtPlot::xBottom, scaleEngine );

QwtDateScaleDraw *scaleDraw = new DateScaleDraw(Qt::UTC );
    QwtDateScaleEngine *scaleEngine = new QwtDateScaleEngine(Qt::UTC);

    setAxisScaleDraw( QwtPlot::xBottom, scaleDraw );
    setAxisScaleEngine( QwtPlot::xBottom, scaleEngine );

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When my program starts the chart displays an empty canvas with the time scale starting at 1970, which is fine. However, as soon as data comes in from the timer the x axis readjusts to years, instead of seconds (how it should be, as far as I know) and the following happens:



The points all get compressed on to the same line, since they are all only seconds apart and the axis is adjusting to years.

How can I force a fixed interval between the points (say, 60 seconds/minutes/hours/etc), I already have the moving and scrolling code in place after this interval is set, I'm just unsure as to how to do it for time values.

For non-time points I do this:

setAxisScale(QwtPlot::xBottom, m_curves[0]->data()->size()-m_pointsToDisplay, m_curves[0]->data()->size());

setAxisScale(QwtPlot::xBottom, m_curves[0]->data()->size()-m_pointsToDisplay, m_curves[0]->data()->size());

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Which gives me a nice interval of size m_pointsToDisplay, but it doesn't seem to work for the datetime engine.

Thanks, OC.

Edit: Nevermind, I got it. I did the following, for whomever is interested:

double startx = data->sample(data->size()-m_pointsToDisplay).x();
        double endx = data->sample(data->size()-1).x();
        setAxisScale(QwtPlot::xBottom, startx, endx);

double startx = data->sample(data->size()-m_pointsToDisplay).x();
        double endx = data->sample(data->size()-1).x();
        setAxisScale(QwtPlot::xBottom, startx, endx);

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My data samples are in ms since epoch, so that worked well. Thanks anyhow, awesome work Uwe (In case you see this)