How to make the x-Bottom scale fixed.

[Tavit]

Hi friends i have a problem with my Plotting program. I have a db in which i save the data i have acquired. Initially the db is empty with no values. I need to have a fixed time scale from 0 to 60 seconds. Now once i click the start acquisition button i have to start acquiring data from a external device and save it to the DB and plot it. Its real time plotting. so i have to plot as i acquire the data. But the x-bottom scale changes according to the amount of data present in the db.
example - If i have only 4 values acquired to the DB the scale is changed to [0 to 3]. It looks like the image i have attached named (3).

If have say 40 values are added to the db the scale is changed to 35. It looks like the image i have attached named (35)

I actually wanted the scale to stay fixed to 60 and the graph to grow from the initial value as the data keeps adding in the graph has to grow gradually.Some thing like the snapshot (60) i have attached.

what do i need to do so that the x-bottom scale is fixed and the data to be plotted with out changing the scale irrespective of the amount of data present in the DB like in the image named (60).


Thank You
Please looking forward for a reply.

[Tavit]

Hi friends how do i fix the the x-bottom size of a qwt plot widget.

myPlot->setTitle("Data Acquisition");
	myPlot->setAxisTitle(QwtPlot::xBottom, "System time");
	myPlot->setAxisScale(QwtPlot::xBottom, 0, 60);
	myPlot->setAxisTitle(QwtPlot::yLeft, "Bar");
	myPlot->setAxisScale(QwtPlot::yLeft, 0, 100);
    myPlot->setAutoReplot(true);

myPlot->setTitle("Data Acquisition");
	myPlot->setAxisTitle(QwtPlot::xBottom, "System time");
	myPlot->setAxisScale(QwtPlot::xBottom, 0, 60);
	myPlot->setAxisTitle(QwtPlot::yLeft, "Bar");
	myPlot->setAxisScale(QwtPlot::yLeft, 0, 100);
    myPlot->setAutoReplot(true);

To copy to clipboard, switch view to plain text mode 

I am using the above code to set the x-bottom scale from 0 to 60. But when i click the start plotting button the bottom scale is changed according to the number of values present in the db. I wanted the scale to stay at 0 to 60 only and the graph to plot according to the number of values present in the db.I am able to retrive data from the db every second but my only problem is the scale which changes i want it to be fixed. How can i do that. ??


Thank You

[Uwe]

The code above is already what you need to do. Obviously someone else is also changing the scale or re-enables autoscaling.

Uwe

[Tavit]

Hi uwe problem solved. Thank You for the reply.

In my plot function i had this

curve->setPen(QPen(Qt::red));
 //myPlot->setAxisScale(QwtPlot::xBottom, m_vx[0], m_vx[m_vx.count() - 1]);

curve->setPen(QPen(Qt::red));
 //myPlot->setAxisScale(QwtPlot::xBottom, m_vx[0], m_vx[m_vx.count() - 1]);

To copy to clipboard, switch view to plain text mode 

Just commented the second line and Bingo. !! But once the graph reaches the x-bottom point 60. I wanted the graph to be cleared and the next graph which again starts with 0 to be started fresh again. I have the data in the db in this format ..

TIME         DATA
0                21
1                24
2                28
3                20
.                  .
.                  .
.                  .
60               24
0                 22
1                 31
2                 26
3                 23
4                 19
.                  .
.                  .
.                  .
60              27

TIME         DATA
0                21
1                24
2                28
3                20
.                  .
.                  .
.                  .
60               24
0                 22
1                 31
2                 26
3                 23
4                 19
.                  .
.                  .
.                  .
60              27

To copy to clipboard, switch view to plain text mode 

Time keeps repeating from 0 to 60 so once the graph is plotted from 0 to 60 it has to be cleared and the graph has to start again from next 0 to 60 and so on. I am not able to figure out how to clear the graph which is displayed on the screen once it reaches 60.Because of this once the graph reaches 60 weird things happen. How should i clear the graph from the screen uwe. ?

Thank You

[Tavit]

Hi uwe i used the clear slot to clear the plot on a button clicked.

void graphplotting::on_pushButton_clicked()
{
myPlot->clear();
}

void graphplotting::on_pushButton_clicked()
{
myPlot->clear();
}

To copy to clipboard, switch view to plain text mode 

But i get a exception error. I tried so much but i still get the same error.
where am i going wrong uwe. !!!


Thank You

[jacek]

Such error appears when you try to access unallocated memory.

When you invoke QwtPlot::clear() it deletes all attached curves, so this error might appear if you access "curve" after push button has been clicked.

[Tavit]

Hi jacek I have looked so much for an example which shows how to clear plots. But cud't find any. I have been tryin since yeste with this problem but cud't slove it. Pls tell me what i have to do to clear this error.



Thank You

[Tavit]

Hi some one pls give me an example to clear( ) a plot . I don't find any on the net. !!!


Thank You

[Tavit]

Hi every one,

I tried so much , I tried the qwt example realtime_plot example in which there is a clear function . Into my program but still i get a exception. Some one pls help me i am really stuck at this place past 2 dazz. !! Tried all the things i cud.But no o/p . Give me a example or tell me how to use the qwtPlot->clear(); in the program.


Thank You

[jacek]

Where do you use "curve" varaible?

[Tavit]

Hello jacek Thankx for the reply, I solved my problem .

void RS232_Receive::retrive() 
{
		{
	 m_curve = new QwtPlotCurve("myPlot");
     myPlot->clear();
	 myPlot->replot();
	 	 //draw();
		}
		draw();	
}
}

void RS232_Receive::retrive() 
{
		{
	 m_curve = new QwtPlotCurve("myPlot");
     myPlot->clear();
	 myPlot->replot();
	 	 //draw();
		}
		draw();	
}
}

To copy to clipboard, switch view to plain text mode 

I did this but once i clear the curve i wanted to call the draw function so that the next values is plotted from start after the present graph is cleared from the screen. But i am not getting it, the new curve is not plotted. !! Where am i going wrong .

Thank You jacek