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Thread: is it possible to plot points without connecting points with line?

  1. #1
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    Default is it possible to plot points without connecting points with line?

    Hi,
    I have two questions. 1- when plotting like below example, points be connected together by lines. I need the points be plotted and there be no line. 2- my data is too huge and i want to use float instead of double but setSamples function gives two "QVector< double > &" . is it possible to use QVector< float > & ???
    for example:
    Qt Code:
    1. QVector<double> v(10);
    2.  
    3. v<<0<<1<<2<<3<<4<<5<<6<<7<<8<<9;//1-is it possible only this points be showed without any line between them?
    4.  
    5. c.setSamples(v, v);//2-how could i use Qvector<float> instead of Qvector<double>?
    6. c.attach(&p);
    7.  
    8. p.show();
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    thanks for any help
    Last edited by Alex22; 13th December 2015 at 20:56.

  2. #2
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    Default Re: is it possible to plot points without connecting points with line?

    Please this post be deleted. i think right position for ask is "Newbie". sorry about this.

  3. #3
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    Default Re: is it possible to plot points without connecting points with line?

    Hello,

    set the curve style to Dots (see qwt documentation of QwtPlotCurve::CurveStyle).

    my data is too huge
    What do you mean by too huge (how many data points)? Qwt can handle really big traces (I use traces with 100 million points), but in this case you have to do some data reduction because default plotting of such a big number of points takes far too much time.

    If you need float for storing your data in your application business logic, you can extract a reduced trace from these data for qwt display. Have a look at the abstract class QwtSeriesData and derive your own series data class from QwtSeriesData< QPointF >. Then use QwtPlotCurve method
    Qt Code:
    1. void setSamples (QwtSeriesData< QPointF > *)
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    . Your QwtSeriesData<> derived class would access your float data, convert them to a pair of double (QPointF) and return this to the curve for plotting.

    I think you have chosen the right place for asking your qwt related question, so from my point of view no need for moving or deleting your question.

    Best regards
    ars

  4. The following user says thank you to ars for this useful post:

    Alex22 (16th December 2015)

  5. #4
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    Default Re: is it possible to plot points without connecting points with line?

    Thanks ars,

    What do you mean by too huge (how many data points)?
    I want to plot more than 10 curves together, each curve has 30,000,000 points. while attaching new curve, speed of plotting goes to be more slower and slower. there is no memory leakage.

    thank you again ars
    Last edited by Alex22; 16th December 2015 at 21:08.

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