TCutG IsInside never tests true

ROOT
1

I am attempting to gate on a TCutG but I can’t get it to ever test true when I use the IsInside method. Please let me know if more information is needed other than what is below…

TCutG cut1(cutName.Data(),fNPoints,fX,fY);
if(cut1.IsInside(csIFast,csISlow)) printf(“cut1=in\n”);

I also tried if(cut1.IsInside(csIFast,csISlow)==1) but that also never tested true.

I double checked that the x and y values had indeed been filled into the TCutG using the GetPoint method and they all appear fine.

what am i missing?!

2

Can you send a small running example reproducing your problem ?

3

i’m not sure how to as it is part of a large and inextricably linked set of classes…created not by me. :frowning: I can try to show more of the code?

  TString cutName;
  Int_t fN[1];
  Double_t fZ[1],fA[1],fX[100],fY[100];
  Int_t detNum=73;
  cutName=Form("det%d",detNum);
  LoadPoints(detNum,fN,fZ,fA,fX,fY);
  Int_t fNPoints=fN[0];
  printf("points:%d\n",fNPoints);
  TCutG cut1(cutName.Data(),fNPoints,fX,fY);

Load points reads in the picked points of the polygon from a file given the detector number.

The program then scrolls through a large event file, event by event, and uses the cut.

if(csIFast>5 && csISlow>5 && siFront>5 && cut1.IsInside(csIFast,csISlow)) { printf("cut 1 passed\n"); hCsITestSlowVsFastFull[csIId-1]->Fill(csIFast,csISlow); fSiCounter[siId]++; }
I don’t know if this makes it any more clear…?

4

That does not really help as we cannot see what the cut points are. I suspect you are outside the cut. Can you draw the cut and save it in a “.C” file from the File/SaveAs menu ?

5

in any kind of just world this is the C file you asked for…
cut.C (1.77 KB)

6

Thanks. It works for me. After:

   cutg->Draw("alp");

I have added:

   Int_t i;
   i = cutg->IsInside(3000.,2000.);
   printf("%d\n",i);                         
   i = cutg->IsInside(2000.,3000.);
   printf("%d\n",i);

And, as expected, the 1st printf gives me 1 and the 2nd 0. Can you try yourself ?

7

It does work with how you showed it. I even got it to go through a scatter plot and only pick out the points that are inside the cut. I still can’t get it to work in my other program- but at least now I know I’m using TCutG correctly. Thanks!

8

I noticed in the above “C file” that the first and last points in the cut are the same. I had been trying to add points to TCutG objects and when I drew them they would never complete the polygon. That is until i added the last line in my code example below

  if(z1cut!=NULL) {delete z1cut; z1cut=NULL;};
  z1cut = new TCutG("z1cut",nz+1);
  z1cut->SetVarX("");
  z1cut->SetVarY("");
  for(Int_t i=0;i<nz+1;i++) {
	z1cut->SetPoint(i,cpntsz[0][i],cpntsz[1][i]);
  }
  z1cut->SetPoint(nz+1,cpntsz[0][0],cpntsz[1][0]);

For clarity the cpntsz array is two dimensional, one for each x-y coordinate. The last line sets the final point of the TCutG equal to the first. This apparently signifies closeure as the IsInside() function doesn’t work properly without this!

9

As indicated in the documentation of TCutG, it must be a closed polygon.
This remark should be probably repeated in several places.

Rene