class TCutG: public TGraph

Graphical cut class

A Graphical cut.

A TCutG object is a closed polygon defining a closed region in a x,y plot. It can be created via the graphics editor option "CutG" or directly by invoking its constructor. The first and last points should be the same.

To create a TCutG via the graphics editor, use the left button to select the points building the contour of the cut. Click on the right button to close the TCutG. When it is created via the graphics editor, the TCutG object is named "CUTG". It is recommended to immediatly change the name by using the context menu item "SetName". When the graphics editor is used, the names of the variables X,Y are automatically taken from the current pad title.

Example:

Assume a TTree object T and:

     Root > T.Draw("abs(fMomemtum)%fEtot")

the TCutG members fVarX, fVary will be set to:

     fVarx = fEtot
     fVary = abs(fMomemtum)

A graphical cut can be used in a TTree selection expression:

    Root > T.Draw("fEtot","cutg1")

where "cutg1" is the name of an existing graphical cut.

Note that, as shown in the example above, a graphical cut may be used in a selection expression when drawing TTrees expressions of 1-d, 2-d or 3-dimensions. The expressions used in TTree::Draw can reference the variables in the fVarX, fVarY of the graphical cut plus other variables.

When the TCutG object is created by TTree::Draw, it is added to the list of special objects in the main TROOT object pointed by gROOT. To retrieve a pointer to this object from the code or command line, do:

    TCutG *mycutg;
    mycutg = (TCutG*)gROOT->GetListOfSpecials()->FindObject("CUTG")
    mycutg->SetName("mycutg");

When the TCutG is not created via TTree::Draw, one must set the variable names corresponding to x,y if one wants to use the cut as input to TTree::Draw,eg

   TCutG *cutg = new TCutG("mycut",5);
   cutg->SetVarX("y");
   cutg->SetVarY("x");
   cutg->SetPoint(0,-0.3586207,1.509534);
   cutg->SetPoint(1,-1.894181,-0.529661);
   cutg->SetPoint(2,0.07780173,-1.21822);
   cutg->SetPoint(3,-1.0375,-0.07944915);
   cutg->SetPoint(4,0.756681,0.1853814);
   cutg->SetPoint(5,-0.3586207,1.509534);

Example of use of a TCutG in TTree::Draw:

   tree.Draw("x:y","mycutg && z>0 %% sqrt(x)>1")

A Graphical cut may be drawn via TGraph::Draw. It can be edited like a normal TGraph.

A Graphical cut may be saved to a file via TCutG::Write.