How to retain previous values in graph? QWT

[maarvi]

Hello everyone!

I am new to qwt and I am facing a problem that when I refresh my graph after 10 seconds my old graph is removed and new is plotted. What I want though is that my previous graph is retained and new values get plotted into the existing plot. Is there a way to do this?

Here is my code (its just start code I have to so improvements in it also the data is large i can not plot it again from the start)

Kindly help me, here is the code :

double xs[100];
double yT[100];
double yP[100];
static int j=0;
myplot::myplot()
{
// add curves
QwtPlotCurve *curveT = new QwtPlotCurve("Temperature");
curveT->setPen(QPen(Qt::red,1));
QwtPlotCurve *curveP = new QwtPlotCurve("Pressure");
curveP->setPen(QPen(Qt::green,1));
for (int i = 0; i < 100; i ++)
{
xs[i] = j;
yT[i] = j;
yP[i] = j+10;
j++;
}

curveT->setRawSamples(xs,yT,100);

curveP->setRawSamples(xs,yP,100);
curveT->attach(this);
curveP->attach(this);
(void)startTimer(1000);

}
void myplot::newValues()
{
for (int i = 0; i < 100; i ++)
{
xs[i] = j+20;
yT[i] = j+20;
yP[i] = j+30;
j++;
}


}
void myplot::timerEvent(QTimerEvent * )
{
newValues();
replot();
}

[FelixB]

What I want though is that my previous graph is retained and new values get plotted into the existing plot. Is there a way to do this?

So, you want to create two new curves (one for temperature and one for pressure) each time "newValues()" is called?

Then you should not overwrite the old values. Create new curves and attach them to your plot.

edit: please, use CODE-tags when you post source code...

[maarvi]

ok sir thanks for your kind reply

but the data is increasing continuously like 24 hr will it be ok?also sir kindly quide me a little more as i am first time using QWT

[FelixB]

but the data is increasing continuously like 24 hr will it be ok?

I don't know if that will be ok. but, when you add two curves each second, I strongly assume that the plot will look very confusing with thousands of curves....

[maarvi]

sir i have made following changes but it didnt work

double xs[10];
double yT[10];
double yP[10];
static int j=0;
myplot::myplot()
{
setTitle("A Simple QwtPlot Demonstration");
// insertLegend(new QwtLegend(), QwtPlot::RightLegend);
// Set axes
// QwtInterval d_interval;
setAxisTitle(xBottom, "time (sec)");
setAxisScale(QwtPlot::xBottom,0,600,30);
// setIntervalLength(20);

setAxisTitle(yLeft, "Payload");
setAxisScale(yLeft, 0,1000 ,10.0);

// add curves
QwtPlotCurve *curveT = new QwtPlotCurve("Temperature");
curveT->setPen(QPen(Qt::red,1));
QwtPlotCurve *curveP = new QwtPlotCurve("Pressure");
curveP->setPen(QPen(Qt::green,1));
for (int i = 0; i < 10; i ++)
{
xs[i] = j;
yT[i] = j;
yP[i] = j+10;
j++;
}

curveT->setRawSamples(xs,yT,10);

curveP->setRawSamples(xs,yP,10);
curveT->attach(this);
curveP->attach(this);
(void)startTimer(1000);

}
void myplot::newValues()
{

QwtPlotCurve *curveT = new QwtPlotCurve("Temperature");
curveT->setPen(QPen(Qt::red,1));
QwtPlotCurve *curveP = new QwtPlotCurve("Pressure");
curveP->setPen(QPen(Qt::green,1));


for (int i = 0; i < 10; i ++)
{
xs[i] = j+20;
yT[i] = j+20;
yP[i] = j+30;
j++;
}

curveT->setRawSamples(xs,yT,10);

curveP->setRawSamples(xs,yP,10);
curveT->attach(this);
curveP->attach(this);

}
void myplot::timerEvent(QTimerEvent * )
{


newValues();
replot();
}

[FelixB]

use "setSamples()" instead of "setRawSamples()". "setSamples()" copies the data while "setRawSamples()" only uses a reference.

I assume, you are using Qwt 6, in the documentation of QwtPlotCurve I don't find a method "setRawSamples()". Uwe probably changed the name from "setRawData()". What I want to say, maybe you don't have a method "setSamples()". Try "setData()" then.

and please, use code tags when you post source code...

[maarvi]

Sorry gfor inconvenience and thanks for ur concern


Sir i have used setSample() but its not working with timer my graphs it not even reploting
what should i do kindly help

thank

[FelixB]

whether you use "setSamples" or "setRawSamples" has absolutely nothing to do with your timer. did you debug if "timerEvent" gets called?

[maarvi]

thanks alot sir my this problem is solved u are awesome..

but kindly tell me is there a way by which my to points get joined after 10 sec as now my two line get joined after 10 sec
thanks you kindly help me

[FelixB]

I'm sorry, I don't understand what you mean with "join two points". can you explain a bit more detailed?

[maarvi]

sir i mean that i have some points like (0,0) (30, 200) ,(60,150)........ so one i want to plot the graph i want that my graph should appear like moving graph in which joins two points for eg (30,200) to (60 ,150) gradually and then join the next two points

should i have to insert timer in my setSample if yes then how or what else i could do

thanks so much

[FelixB]

that sounds quite complicated. I have no idea how to do that at the moment. is the time between two points fixed? e.g. do you want to reach the next point always after x seconds? or is it dependant of the distance between the points, e.g. very short from (0,0) to (1,1) and very long time from (1,1) to (100,100)?

[maarvi]

sir actually the distance alond x axis is fixed.the interval is 30 but y axis changes. and time should be same no need that for longer distance more time required

thanks