Focusing a TH1I histogram on a previously seen region

Purpose : To focus the display of the histogram on a particular region of interest(ROI)
between repeated calls to load_data. Suppose the histogram has 32000 points
and we want to focus the histogram display between x=1000 and x=2000.
Now suppose we change our ROI to another area using the finger tool widget displayed
when we take the mouse cursor near the x-axis …just below it.
What function to use and where to locate it so that the previously displayed ROI
is maintained between repeated calls to load_data(…)…
Parts of my code is displayed below …
One more help I need is how to label the x-axis depending on the rate of acquisition
of the data points in the histogram.
Suppose the variable rate holds the rate of acquisition of the points
in the 1-D TH1I histogram :
Double_t rate; if rate = 1.0 ; (points acquired at 1 milli second interval)
how to label x-axis in seconds. And if rate = 0.2 ; (0.2 mS) how to label x-axis…
kindly help as the examples given on the internet are not so simple to understand.
forumcpp03.txt (1.86 KB)

Parts of code below :

TH1I *fHpx_waveMCA;
TAxis* x_waveMCA;
TAxis* y_waveMCA;
Int_t xmaxint_waveMCA;
Int_t xminint_waveMCA;
Double_t xmaxdt;
Double_t xmindt;
Double_t ymaxdt;
Double_t ymindt;
TCanvas *c124;

int Wind1::load_data(unsigned short mod3333, unsigned short chan3333)
	int retval;
	unsigned int NumWords ;
	NumWords = 32768;
	char hname1[10] =  "MCA" ;
	if (tracehist == NULL)
		tracehist = new unsigned int[NumWords];
	memset(tracehist, 0, NumWords * sizeof(unsigned int));
	printf("Reading Histogram from module: module no:%i , chan no.:%i \n",mod3333, chan3333);
	Getdata (tracehist, NumWords, mod3333, chan3333);
	if(retval < 0)
	// error handling
		if (retval == -1)
		return 0;
char title01[20] = "data from module" ;
sprintf(histtitle,"%s,mod=%d,chan=%d", title01 ,mod3333, chan3333);
	if (fHpx_waveMCA == NULL ) {
		 	fHpx_waveMCA = new TH1I ( hname1 , histtitle , NumWords, 0, NumWords );  
			x_waveMCA = fHpx_waveMCA->GetXaxis();
		//	y_waveMCA = fHpx_waveMCA->GetYaxis(); // for y-axis
	xmaxint_waveMCA = x_waveMCA->GetLast();
	xminint_waveMCA = x_waveMCA->GetFirst();
//  for y - axis
//	ymaxdt = fHpx_waveMCA->GetMaximum();
//	ymindt = fHpx_waveMCA->GetMinimum();
 	fHpx_waveMCA = new TH1I ( hname1 , histtitle , NumWords, 0, NumWords );  
	for ( int i = 0; i < NumWords ; i++)
		{  fHpx_waveMCA->Fill(i, int(tracehist[i]) );
	xmaxdt = (Double_t) 2000 ; //   xmaxint_waveMCA;
	xmindt = (Double_t) 1000 ; //   xminint_waveMCA;
	fHpx_waveMCA->SetAxisRange(xmindt, xmaxdt, "X");
//	fHpx_waveMCA->SetAxisRange(ymindt, ymaxdt, "Y");  // for y-axis
return 1;
}  // int Wind1::load_data(unsigned short mod3333, unsigned short chan3333)

The previous settings I am getting from the following lines before Reset and fill of Histogram :
xmaxint_waveMCA = x_waveMCA->GetLast();
xminint_waveMCA = x_waveMCA->GetFirst();
and I try to set it again after the Reset and fill of the Histogram , but this does not work.
The whole range of the histogram is displayed again… #-o #-o #-o

Sorry for the late answer I was away.
Did you find a solution meanwhile ?

No, I have not yet found an answer. I have been thinking about the solution to this problem and
I plan to use two double pointer sliders, one for each axis, placed at the external edges of the
histogram window to set the range of the axis - x and y. when I get time to implement it and get
it working I will post a reply. #-o #-o #-o

Ok. Let us know.

I ended up requiring double slider only for the x-axis as the y-axis was auto ranging,
In case I may need it in future then I will have to implement the vertical double
slider also, which is similar to the horizontal double slider for which I have added
the following to my code:

In header file add:

#include "TGSlider.h"
#include "TGDoubleSlider.h"
  TGDoubleHSlider *fHSlider1031;
Float_t	WindowHWmax;
Float_t	WindowHWmin;

In mycode.cpp file in constructor:
   fHSlider1031 = new TGDoubleHSlider(fVerticalFrame770,1016, kScaleBoth ,-1,kHorizontalFrame); 
   fHSlider1031->SetRange(0,int (NumWords) );  // NumWords holds the max range value of x-axis
   fVerticalFrame770->AddFrame(fHSlider1031, new TGLayoutHints(kLHintsLeft | kLHintsTop,2,2,2,2));
Bool_t HistWin::ProcessMessage (Long_t msg, Long_t parm1, Long_t parm2)
cout << "msg = " << msg << ", parm1 = " << parm1 << ", parm2 = " << parm2 << '\n' ;
  switch (GET_MSG (msg))
      case kC_COMMAND:
	case kC_HSLIDER:
	{	cout << "I am in Slider code" << "\n" ;
		WindowHWmax = fHSlider1031->GetMaxPosition();
		WindowHWmin = fHSlider1031->GetMinPosition();
		cout << "WindowHWmin = " << WindowHWmin << " WindowHWmax = " << WindowHWmax "\n";
		fHpx_waveMCA->SetAxisRange(WindowHWmin, WindowHWmax, "X");
	cout << "I am here 007" << "\n";
	c124->cd();cout << "I am here 008" << "\n";
	fHpx_waveMCA->DrawCopy();cout << "I am here 009" << "\n";
	c124->Modified();cout << "I am here 010" << "\n";
	c124->Update();cout << "I am here 011" << "\n";
	gSystem->ProcessEvents();cout << "I am here 012" << "\n";

And in load_data() function
fHpx_waveMCA->SetAxisRange(WindowHWmin, WindowHWmax, "X");

I wrote the code last week, tested it out for a week.
The code works excellently, brilliantly, simply superb,… :slight_smile: :smiley: =D>
Hope this is of help to the root coder community.