how to load data file and plot from the datafile

[charu]

hi
I am charu, totally New to Qwt , i have to plot from .txt file containing floating point. i want to know how to load/read a datafile and plot it row by row (that is: one value by one)
thank you for ur grt help

[huseyinkozan]

hi
I am charu, totally New to Qwt , i have to plot from .txt file containing floating point. i want to know how to load/read a datafile and plot it row by row (that is: one value by one)
thank you for ur grt help

Hi charu,
I also new. I wrote something similar to load data from text file:

QFile file("./data.txt");
	if (!file.open(QIODevice::ReadOnly | QIODevice::Text))
		return;
	QStringList list;
	QTextStream in(&file);
	while (!in.atEnd()) {
		list << in.readLine();
	}
	data = new double[list.size()];
	for(int i = 0; i< list.size(); i++){
		data[i] = list[i].toDouble();
	}
	dataSize = list.size();

QFile file("./data.txt");
	if (!file.open(QIODevice::ReadOnly | QIODevice::Text))
		return;
	QStringList list;
	QTextStream in(&file);
	while (!in.atEnd()) {
		list << in.readLine();
	}
	data = new double[list.size()];
	for(int i = 0; i< list.size(); i++){
		data[i] = list[i].toDouble();
	}
	dataSize = list.size();

To copy to clipboard, switch view to plain text mode 

And the data.txt in this format:

1.8600000e+03
1.8640000e+03
1.8660000e+03
1.8550000e+03
1.8660000e+03
1.8760000e+03

For plotting, you can look at the examples (simple plot maybe).
Good luck.


Hüseyin

[charu]

thank you so much

Now i need to Plot the data ?
can u plz tell me how to plot? I am using QT3 and QWT5.1.1

[huseyinkozan]

thank you so much

Now i need to Plot the data ?
can u plz tell me how to plot? I am using QT3 and QWT5.1.1

Sorry, I don't have Qt3.
Also I don't know the difference between 3 and 4.
Maybe both are same for simple things.

For plotting I am using double array, and QwtPlotCurve::setRawData() in a derived QwtPlot class.

You can also use setData().
Simply like this: (From QwtPlot Class Reference)

#include <qwt_plot.h>
#include <qwt_plot_curve.h>
 
QwtPlot *myPlot;
double x[100], y1[100], y2[100];        // x and y values
 
myPlot = new QwtPlot("Two Curves", parent);
 
// add curves
QwtPlotCurve *curve1 = new QwtPlotCurve("Curve 1");
QwtPlotCurve *curve2 = new QwtPlotCurve("Curve 2");
 
getSomeValues(x, y1, y2);
 
// copy the data into the curves
curve1->setData(x, y1, 100);
curve2->setData(x, y2, 100);
 
curve1->attach(myPlot);
curve2->attach(myPlot);
 
// finally, refresh the plot
myPlot->replot();

#include <qwt_plot.h>
#include <qwt_plot_curve.h>

QwtPlot *myPlot;
double x[100], y1[100], y2[100];        // x and y values

myPlot = new QwtPlot("Two Curves", parent);

// add curves
QwtPlotCurve *curve1 = new QwtPlotCurve("Curve 1");
QwtPlotCurve *curve2 = new QwtPlotCurve("Curve 2");

getSomeValues(x, y1, y2);

// copy the data into the curves
curve1->setData(x, y1, 100);
curve2->setData(x, y2, 100);

curve1->attach(myPlot);
curve2->attach(myPlot);

// finally, refresh the plot
myPlot->replot();

To copy to clipboard, switch view to plain text mode 

In getSomeValues(x, y1, y2) simply copy the data to the double buffers.


Hüseyin

[charu]

thanks

i have error:expected constructor,destructor, or type conversion before'=' token..... hence i commented each line by line
1) no errors with include file alone
2) error started from myplot=... onwards .
i dont have any idea to solve this can you plz let me know what could be the problem on my program.

procedure i created the project:
1) New Project
2) New Widget
3) New main.cpp
copied ur code in the form1.ui.h and qmake, make ....errors plz help me

thank u in advance

[huseyinkozan]

thanks

i have error:expected constructor,destructor, or type conversion before'=' token..... hence i commented each line by line
1) no errors with include file alone
2) error started from myplot=... onwards .
i dont have any idea to solve this can you plz let me know what could be the problem on my program.

procedure i created the project:
1) New Project
2) New Widget
3) New main.cpp
copied ur code in the form1.ui.h and qmake, make ....errors plz help me

thank u in advance

It could be many different things; maybe header problem, or trying to reach a pointer out of scope....I don't know.
Now, its your turn to figure it out.
Act like a detective, and find the problem. Maybe you should turn back to some fundamentals.

Good luck.


Hüseyin

[charu]

thanks i got it

After incliding the lib file i can plot.

but the getSomeValues(); is not working, so i generated some x,y values and ploted

thank you so much 4r ur grt help