PyQT QwtScaleDiv adds ticks to axis

**mbernasocchi** · 16th March 2011, 11:58

Hi, i'm implementing my own QwtScaleDraw like that:

Qt Code:

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class TimeScaleDraw(QwtScaleDraw):
    def __init__(self, baseTime):
        QwtScaleDraw.__init__(self)
        #QTime baseTime
        self.baseTime = baseTime
        self.setLabelAlignment(Qt.AlignLeft | Qt.AlignBottom)
        self.setLabelRotation(-25.0)
 
    def label(self, secs):
        upTime = self.baseTime.addSecs(secs)
        upTime = upTime.toString('dd MM yy hh:mm:ss')
        return QwtText(upTime)

class TimeScaleDraw(QwtScaleDraw):
    def __init__(self, baseTime):
        QwtScaleDraw.__init__(self)
        #QTime baseTime
        self.baseTime = baseTime
        self.setLabelAlignment(Qt.AlignLeft | Qt.AlignBottom)
        self.setLabelRotation(-25.0)

    def label(self, secs):
        upTime = self.baseTime.addSecs(secs)
        upTime = upTime.toString('dd MM yy hh:mm:ss')
        return QwtText(upTime)

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then I use it this way:

Qt Code:

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ticks = [0, 60, 120]
div = QwtScaleDiv()
div.setInterval(ticks[0], ticks[len(ticks)-1])
div.setTicks(QwtScaleDiv.MinorTick, [])
div.setTicks(QwtScaleDiv.MediumTick, [])
div.setTicks(QwtScaleDiv.MajorTick, ticks)
draw = TimeScaleDraw(QDateTime(self.main.timeMin))
draw.setScaleDiv(div)
self.plot.setAxisScaleDraw(QwtPlot.xBottom, draw)
self.plot.setAxisScale(QwtPlot.yLeft, self.main.valueMin, self.main.valueMax)

ticks = [0, 60, 120]
div = QwtScaleDiv()
div.setInterval(ticks[0], ticks[len(ticks)-1])
div.setTicks(QwtScaleDiv.MinorTick, [])
div.setTicks(QwtScaleDiv.MediumTick, [])
div.setTicks(QwtScaleDiv.MajorTick, ticks)
draw = TimeScaleDraw(QDateTime(self.main.timeMin))
draw.setScaleDiv(div)
self.plot.setAxisScaleDraw(QwtPlot.xBottom, draw)
self.plot.setAxisScale(QwtPlot.yLeft, self.main.valueMin, self.main.valueMax)

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I'd like to have only 3 ticks (where there actually are values) on my x axis, but some how I get more ticks added (see screen shot). what do i do wrong? any suggestion?

**Uwe** · 16th March 2011, 18:45

Use QwtPlot::setAxisScaleDiv() - the ticks directly assigned to your scaleDraw object will be overwritten by the next replot.

Uwe

**mbernasocchi** · 17th March 2011, 10:11

Hi Uwe, thanks for the reply, I had tryed it already and the result was worse, but I tryed it again just to be shure. it does not work (see attach).
my code is:

Qt Code:

Switch view

ticks = [0, 60, 120]
div = QwtScaleDiv()
div.setInterval(ticks[0], ticks[len(ticks)-1])
div.setTicks(QwtScaleDiv.MinorTick, [])
div.setTicks(QwtScaleDiv.MediumTick, [])
div.setTicks(QwtScaleDiv.MajorTick, ticks)
draw = TimeScaleDraw(QDateTime(self.main.timeMin))
#draw.setScaleDiv(div)
self.plot.setAxisScaleDiv(QwtPlot.xBottom, div)
self.plot.setAxisScaleDraw(QwtPlot.xBottom, draw)
self.plot.setAxisScale(QwtPlot.yLeft, self.main.valueMin, self.main.valueMax)

ticks = [0, 60, 120]
div = QwtScaleDiv()
div.setInterval(ticks[0], ticks[len(ticks)-1])
div.setTicks(QwtScaleDiv.MinorTick, [])
div.setTicks(QwtScaleDiv.MediumTick, [])
div.setTicks(QwtScaleDiv.MajorTick, ticks)
draw = TimeScaleDraw(QDateTime(self.main.timeMin))
#draw.setScaleDiv(div)
self.plot.setAxisScaleDiv(QwtPlot.xBottom, div)
self.plot.setAxisScaleDraw(QwtPlot.xBottom, draw)
self.plot.setAxisScale(QwtPlot.yLeft, self.main.valueMin, self.main.valueMax)

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**corrado1972** · 29th March 2011, 13:05

Hi, did you solved ?
bye

**mbernasocchi** · 29th March 2011, 17:08

no

any ideas?

**Uwe** · 29th March 2011, 18:48

What type of answer do you expect for "it does not work" ?

Uwe

**mbernasocchi** · 7th April 2011, 22:50

Hi Uwe, well the situation for me is that I've the following code:

Qt Code:

Switch view

ticks = [0, 60, 120]
div = QwtScaleDiv()
div.setInterval(ticks[0], ticks[len(ticks)-1])
div.setTicks(QwtScaleDiv.MinorTick, [])
div.setTicks(QwtScaleDiv.MediumTick, [])
div.setTicks(QwtScaleDiv.MajorTick, ticks)
draw = TimeScaleDraw(QDateTime(self.main.timeMin))
#draw.setScaleDiv(div)
self.plot.setAxisScaleDiv(QwtPlot.xBottom, div)
self.plot.setAxisScaleDraw(QwtPlot.xBottom, draw)
self.plot.setAxisScale(QwtPlot.yLeft, self.main.valueMin, self.main.valueMax)

ticks = [0, 60, 120]
div = QwtScaleDiv()
div.setInterval(ticks[0], ticks[len(ticks)-1])
div.setTicks(QwtScaleDiv.MinorTick, [])
div.setTicks(QwtScaleDiv.MediumTick, [])
div.setTicks(QwtScaleDiv.MajorTick, ticks)
draw = TimeScaleDraw(QDateTime(self.main.timeMin))
#draw.setScaleDiv(div)
self.plot.setAxisScaleDiv(QwtPlot.xBottom, div)
self.plot.setAxisScaleDraw(QwtPlot.xBottom, draw)
self.plot.setAxisScale(QwtPlot.yLeft, self.main.valueMin, self.main.valueMax)

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which instead of generating only 3 major ticks at the desired location it creates many more ticks as shown in the attachement in the post above. you can see the full code at http://hub.qgis.org/projects/multivi...eplotwidget.py i'd be super if you could give me an hint...
thanks a lot
Marco

**Uwe** · 11th April 2011, 07:09

QwtScaleDiv internally has a flag, that indicates if it is valid or not - if not it gets recalculated from the autoscaler. Of course this is a bad class design and has to do with the history of the QwtScaleDiv class.

Instead you have to initialize your QwtScaleDiv object this way ( C++ ):

Qt Code:

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QList<double> ticks[QwtScaleDiv::NTickTypes];
ticks[QwtScaleDiv::MajorTick] << 0.0 << 60.0 << 120.0;
 
QwtScaleDiv scaleDiv( 
    ticks[QwtScaleDiv::MajorTick].first(),
    ticks[QwtScaleDiv::MajorTick].last(), 
    ticks );
 
setAxisScaleDiv(QwtPlot::xBottom, scaleDiv);

QList<double> ticks[QwtScaleDiv::NTickTypes];
ticks[QwtScaleDiv::MajorTick] << 0.0 << 60.0 << 120.0;

QwtScaleDiv scaleDiv( 
    ticks[QwtScaleDiv::MajorTick].first(),
    ticks[QwtScaleDiv::MajorTick].last(), 
    ticks );

setAxisScaleDiv(QwtPlot::xBottom, scaleDiv);

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Uwe

**mbernasocchi** · 11th April 2011, 12:31

Hi Uwe, thanks for the answer, I tried and it almost works, now I just dont' have the labels anymore (the ticks are at the right place). (see screenshot and note that the picker shows the correct value)
the code I use is:

Qt Code:

Switch view

#update axes
            div = QwtScaleDiv(ticks[0], ticks[len(ticks)-1], ticks, [],[])
            baseTime = QDateTime(self.mainWidget.timeMin)
            draw = TimeScaleDraw(baseTime)
            self.plot.setAxisScaleDraw(QwtPlot.xBottom, draw)
            self.plot.setAxisScaleDiv(QwtPlot.xBottom, div)
 
class TimeScaleDraw(QwtScaleDraw):
    def __init__(self, baseTime):
        QwtScaleDraw.__init__(self)
        #QTime baseTime
        self.baseTime = baseTime
        self.setLabelAlignment(Qt.AlignLeft | Qt.AlignBottom)
        self.setLabelRotation(-25.0)
 
    def label(self, secs):
        upTime = self.baseTime.addSecs(secs)
        upTime = upTime.toString('dd MM yy hh:mm:ss')
        return QwtText(upTime)

#update axes
            div = QwtScaleDiv(ticks[0], ticks[len(ticks)-1], ticks, [],[])
            baseTime = QDateTime(self.mainWidget.timeMin)
            draw = TimeScaleDraw(baseTime)
            self.plot.setAxisScaleDraw(QwtPlot.xBottom, draw)
            self.plot.setAxisScaleDiv(QwtPlot.xBottom, div)

class TimeScaleDraw(QwtScaleDraw):
    def __init__(self, baseTime):
        QwtScaleDraw.__init__(self)
        #QTime baseTime
        self.baseTime = baseTime
        self.setLabelAlignment(Qt.AlignLeft | Qt.AlignBottom)
        self.setLabelRotation(-25.0)

    def label(self, secs):
        upTime = self.baseTime.addSecs(secs)
        upTime = upTime.toString('dd MM yy hh:mm:ss')
        return QwtText(upTime)

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as well, using python one has to know this: http://pyqwt.sourceforge.net/doc5/re...t5.QwtScaleDiv
do you have an idea why this happens?
Screenshot.jpg
thanks Marco

**Uwe** · 13th April 2011, 08:37

Is your overloaded label method called - and if yes with which values ?

Uwe

**mbernasocchi** · 13th April 2011, 10:12

Hi uwe, spot on... no it si not called, when I dont use the

Qt Code:

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self.plot.setAxisScaleDiv(QwtPlot.xBottom, div)

self.plot.setAxisScaleDiv(QwtPlot.xBottom, div)

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line then it gets called automatically with the correct values. Do I need to call it myself? where?
ciao Marco

Added after 40 minutes:

Uwe, btw, it is not only my overloaded label that doesn't get called, if I remove the label method in my QwtScaleDraw, nothing changes, the labels are not drawn.

**Uwe** · 13th April 2011, 10:59

labels are painted for major ticks only. I'm not familiar with the Python API, but maybe the ticks you have set are the minor or medium ticks ?

Uwe

**mbernasocchi** · 13th April 2011, 11:29

Uwe thanks a lot... you do indeeed know your "baby" by heart. i think there is a bug in the python API documentation. by changing:

Qt Code:

Switch view

div = QwtScaleDiv(ticks[0], ticks[len(ticks)-1], [], [], ticks)

div = QwtScaleDiv(ticks[0], ticks[len(ticks)-1], [], [], ticks)

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to

Qt Code:

Switch view

div = QwtScaleDiv(ticks[0], ticks[len(ticks)-1], ticks, [], [])

div = QwtScaleDiv(ticks[0], ticks[len(ticks)-1], ticks, [], [])

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it all works although the documentation it says:

scaleDiv = QwtScaleDiv(
lower, upper, majorTicks, mediumTicks, minorTicks)

I'll contact the API author. thanks a lot Again
ciao Marco
working.jpg

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