Time in x - axis

[Faramia]

Hello together,

i use qwt and its a nice tool but i am a newbie (work on it

i have problems to implement a time in my x-axis.

I want to display datas on the x-axis (from 08:00 clock to 20:00 clock)
The y-axis are simple values from 0-100...

i got the data for the clock values in a simple string for example: 160025 (hhmmss) (x-axis value) and another value y-axis = 10.

i dont know how to implement the x-axis to draw a correct time/clock distance...

Sorry for my bad english

Thank in advance for any help!
Faramia

[desantossierra]

Hi Faramia,

you have create a new class deriving from QwtScaleDraw and re-implement the QwtText label (double) const; method

When you have your new class, you have to attach it in your plot, like this

QwtScaleDrawTime *scaleTime = new QwtScaleDrawTime;
plot->setAxisScaleDraw(QwtPlot::xBottom,scaleTime);

Sorry for my bad english too.

[FelixB]

Hi,

that is really quite easy. desantosseria already tolod you how to do that.

Additionally, have a look at the examples delivered with qwt. there is at least one example using a time axis (don't ask me which one, might be "CPUPlot" or something thelike).

Felix

[Faramia]

Hi Thanks for your replys desantossierra and FelixB.

My new QwtScaleDrawClass looks like: i dont think this is the right way
"i" is a static var which holds the counter for the hours...

class QwtScaleDrawTime: public QwtScaleDraw
{
public:
    QwtScaleDrawTime(const QTime &base):
        baseTime(base)
    {
    }
    virtual QwtText label(double v) const
    {
        i++;
        qDebug() << "basetime to string" << baseTime.toString() << "v:" << v << "i:" << i;
        qDebug() << baseTime.addSecs(3600*i).toString();
        return baseTime.addSecs(3600*i).toString();
    }
private:
    QTime baseTime;
    static int i;
};

class QwtScaleDrawTime: public QwtScaleDraw
{
public:
    QwtScaleDrawTime(const QTime &base):
        baseTime(base)
    {
    }
    virtual QwtText label(double v) const
    {
        i++;
        qDebug() << "basetime to string" << baseTime.toString() << "v:" << v << "i:" << i;
        qDebug() << baseTime.addSecs(3600*i).toString();
        return baseTime.addSecs(3600*i).toString();
    }
private:
    QTime baseTime;
    static int i;
};

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implements to my plot:
i set the default time to 7:00 to achieve a x-axis from 8-to20. but it doesnt work really well
it draws on the x-axis 8:00, 10:00 ,11:00....20:00, 09:00... Why is the 09:00 at the end of the x-axis?

setAxisScale(xBottom, 08.00, 20.00, 1);
 QTime myTime(7,00);
  setAxisScaleDraw(QwtPlot::xBottom,
                     new QwtScaleDrawTime(myTime));

setAxisScale(xBottom, 08.00, 20.00, 1);
 QTime myTime(7,00);
  setAxisScaleDraw(QwtPlot::xBottom,
                     new QwtScaleDrawTime(myTime));

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i THink i dont get the point, how to implement it -.-

Sorry for that.

Faramia

[desantossierra]

Hi Faramia,

the main idea is that you have the normal x-axis in the plot, I mean
x from 1 to ...
and you have to convert to hours, in the label method
for example, when x = 1 then hour = 7:00

virtual QwtText label(double v) const v is the x-value in the plot
{
// check if v is an integer value

// if yes do this
qDebug() << "basetime to string" << baseTime.toString() << "v:" << v << "i:" << i;
qDebug() << baseTime.addSecs(3600*v).toString();
return baseTime.addSecs(3600*v).toString();
// if not
return EMPTY_STRING;
}

then, you have to change your code to

setAxisScale(xBottom, 1,1+numOfHours, 1); // numOfHours = number of hours you want to show
QTime myTime(7,00);
setAxisScaleDraw(QwtPlot::xBottom,
new QwtScaleDrawTime(myTime));

[Faramia]

Thank you very much desantossierra!,

this helps really a lot!

for my understanding i have to map all the x-values, right?

that means for example:
value1: y = 5, x=08:00 clock,
value2: y = 10, x = 08:25...
value3: y= 3, x = 9:45...

so the first value for x is 0800, -> x = 1 ( if 8:00 is the startvalue for the x-axis.)
2nd value x 08:25 -> x = 1,41 - for correct display ?
3rd value x 9:45, -> x = 2,75 - for correct display ?

TIA
Faramia

[desantossierra]

mmm...

why x=1,41?

for example, if x is the double value of the label method then you could use something like this

int hour = (floor(x) + initHour ) % 24 ;
int minute = 60*(x - floor(x));
return QwtText(QString('%1:%2').arg(hour).arg(minute));

[Faramia]

Thank you again desantossierra,

i will try ur solution.

i thought and tested it, that the x-axis values starts every time with 1. (not the label, the values in the plot.... - for example, if i start wiht 8:00 to 15:00 (x axis labels...) and if i want to display a x value with y = 5 and x = 8:00, i have to map x to 1 to set the correct display in the plot...
But perhaps i am wrong so i will try your solution.

Thank again and again!

Sorry for my bad english

Faramia

[desantossierra]

don't worry for your english, my english is worse

tell me if works or not

[Faramia]

it works ty!

[oddytz1989]

Hello, I also have a question about the time axis X.
Value for the X axis, I get in the loop from the database in the format of Unix time like 1328612875.
From the example cpuplot, write the following:

class TimeScaleDraw: public QwtScaleDraw
{
public:
    TimeScaleDraw(const QTime &base):
        baseTime(base)
    {
    }
    virtual QwtText label(double v) const
    {
 
        QTime upTime = baseTime.addSecs((int)v);
        return upTime.toString();
    }
private:
    QTime baseTime;
};
 
 
QTime TrendTop::upTime() const
{
    QTime t;
    t=QTime::currentTime();
    return t;
}

class TimeScaleDraw: public QwtScaleDraw
{
public:
    TimeScaleDraw(const QTime &base):
        baseTime(base)
    {
    }
    virtual QwtText label(double v) const
    {

        QTime upTime = baseTime.addSecs((int)v);
        return upTime.toString();
    }
private:
    QTime baseTime;
};


QTime TrendTop::upTime() const
{
    QTime t;
    t=QTime::currentTime();
    return t;
}

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But time is displayed on the X axis does not correspond to reality.
Can you please tell what I need to fix?