TGaxis title alignment

ROOT
1

Hi there,

I’m trying to scale my histogram axis by hand, i.e. painting a TGaxis with a different range on top of the TAxis drawn by default. The TGaxis plots fine except for one thing - the title won’t align with the top of the frame. I tried calling TAxis::CenterTitle(kFALSE) and as a cross check also with a kTRUE argument and I can see that it changes the fBits field, but it doesn’t move the axis title. Does anybody know how I can get the title properly aligned with the top of the frame?

Thanks,
Bram

I’m using this weekend’s CVS version compiled into my own code, code snippet below:

   if(hdata->GetMaximum() > 1000) {
  yaxis = new TGaxis(0, 0, 0, hdata->GetMaximum(), 0, hdata->GetMaximum()/1000., 505, "");
  yaxis->ImportAxisAttributes(hdata->GetYaxis());
  hdata->GetYaxis()->SetTitle("");
  hdata->GetYaxis()->SetTitleColor(WHITE);
  hdata->GetYaxis()->SetTitleSize(0.01);
  hdata->GetYaxis()->SetLabelSize(0.01);
  hdata->GetYaxis()->SetLabelColor(WHITE);
  yaxis->SetLabelColor(BLACK);
  yaxis->SetLabelSize(0.07);
  yaxis->SetTitleSize(0.07);
  yaxis->SetTitle(Form("#times1000 entries/%g GeVc^{-1}",(Double_t)(hdata->GetXaxis()->GetXmax()/hdata->GetNbinsX())));
  yaxis->SetTextColor(BLACK);
  yaxis->CenterTitle(kFALSE);
  yaxis->DrawAxis(0, 0, 0, hdata->GetMaximum(), 0, hdata->GetMaximum()/1000., 505, "");
   }
2

Can you send a small example I can run ?

Thanks, Olivier

3

Here goes - the executable should not depend on anything but ROOT, histogram is in the attached file test0.root.

Bram
test0.root (3.75 KB)
test.cxx (1.58 KB)

4

The Yaxis position you choose is not correct. Pad maximum is not the histogram maximum (there is a margin). Change axis color to red and you will see that. Here is a working example:

void test() {
   TCanvas* c1 = new TCanvas("c1", "Test axis");

   gStyle->SetPadLeftMargin(0.14);
   gStyle->SetPadBottomMargin(0.15);
   gStyle->SetLabelSize(0.07, "xyz");
   gStyle->SetTitleSize(0.07, "xyz");
   gStyle->SetTitleH(0.08); // width is adjusted according to string length
   gStyle->SetTitleX(0.14); // flush with the left side of the frame, I hope
   gStyle->SetTitleStyle(0);

   TFile* ftest = new TFile("test0.root", "read");
   TH1F* hdata = (TH1F*) ftest->Get("hPtRelPhi_5");
   hdata->DrawCopy("ep");
   c1->Update();

   TGaxis* yaxis;
   if(hdata->GetMaximum() > 1000) {
      yaxis = new TGaxis(0, 0, 0, gPad->GetUymax(), 0, gPad->GetUymax()/1000., 510, "");     
      yaxis->ImportAxisAttributes(hdata->GetYaxis());
      hdata->GetYaxis()->SetTitleOffset(999.);
      hdata->GetYaxis()->SetLabelOffset(999.);
      hdata->DrawCopy("ep");
      yaxis->SetLineColor(2); 
      yaxis->SetLabelSize(0.03);
      yaxis->SetTitleSize(0.03);
      yaxis->SetTitle("Y Title align on top (use GetUymax)");
      yaxis->Draw();
   }
}
5

Thanks!

I had tried the gPad->Uymax() method before (it’s in the examples) but I never called TPad::Update() , so gPad->Uymax() returned 1.

6

Yes, gPad->Uymax returns the Y maximum value of the current pad. But tobe right, the pad should have been created. That’s what Update() is doing.