Usage of TCanvas::SetTheta() and TCanvas::SetPhi()

ROOT
1

Hi,

I’m confused about the right way of using TCanvas::SetTheta() and TCanvas::SetPhi(). E.g. I would like to draw a TGraph2D with PCOLZ option and view it
a) in the x-y plane
b) in the y-z plane
c)- in the x-z plane.

What values for theta and phi do I have to use you achieve that?

E.g. for c) I tried the following but the result doesn’t look right at all, I assume because I used the wrong values for theta and phi.

TGraph2D *gr = new TGraph2D(3);
gr->SetPoint( 0, -10e-5, 30e-5, 9.);
gr->SetPoint( 1, -9e-5, -30e-5, 7.);
gr->SetPoint( 2, -10e-5, -90e-5, 8.);
gr->SetMarkerStyle(21);
TCanvas* canvas = new TCanvas();
double theta = 0;
double phi = 0;
canvas->SetTheta( theta. );
canvas->SetPhi( phi );
 gr->Draw("pcolz");

Cheers,
Bjorn

2

The simplest is that you position your plot interactively with the mouse and then save the result in a .C file.
Then look in that file what the the values of theta and phi.

3

Hi,

thanks for hint, but now I’m even more confused. It llooks like theta=0, phi=0 gives indeed the x-z-plane but the plot looks only reasonable when I set the range of the hidden y-axis by hand (see UserYRange.png produced by code below). Without doing that the plot looks totally different ( see DefaultYRange.png).

{
TGraph2D *gr = new TGraph2D(3);
  gr->SetPoint( 0, -10e-5, 30e-5, 9.);
  gr->SetPoint( 1, -9e-5, -30e-5, 7.);
  gr->SetPoint( 2, -10e-5, -90e-5, 8.);
  gr->SetMarkerStyle(21);
  gr->GetXaxis()->SetTitle("x axis");
  gr->GetYaxis()->SetTitle("y axis");
  gr->GetZaxis()->SetTitle("z axis");

  TCanvas* canvas = new TCanvas();
  canvas->SetTheta(0);
  canvas->SetPhi(0);

  gr->Draw("pcolz");
  canvas->SaveAs("DefaultYRange.png");

  gr->GetYaxis()->SetRangeUser(-100e-5,50e-5);
  gr->Draw("pcolz");
  canvas->SaveAs("UserYRange.png");
}

Why is the call of SetRangeUser on the hidden axis necessary?

Cheers,
Bjorn

4

Ok lets simplify the issue. When I run:

{
TGraph2D *gr = new TGraph2D(3);
  gr->SetPoint( 0, -10e-5, 30e-5, 9.);
  gr->SetPoint( 1, -9e-5, -30e-5, 7.);
  gr->SetPoint( 2, -10e-5, -90e-5, 8.);
  gr->SetMarkerStyle(21);
  gr->GetXaxis()->SetTitle("x axis");
  gr->GetYaxis()->SetTitle("y axis");
  gr->GetZaxis()->SetTitle("z axis");

  TCanvas* canvas = new TCanvas();

  gr->Draw("pcol");
}

I do not see any point at z=9 … which is weird.
I will investigate that.

5

but :

  gr->SetPoint( 0, 1, 2, 9.);
  gr->SetPoint( 1, 2, 3, 7.);
  gr->SetPoint( 2, 4, 5, 8.);

is ok

6

There is a precision issue I am trying to work around.
Not real solution yet.

7

I found a solution:

{
   Double_t x[3], y[3], z[3];
   
   x[0] = -0.01000; y[0] =  1.00000; z[0] = 9.;
   x[1] = -0.00005; y[1] = -0.00002; z[1] = 7.;
   x[2] = -0.00009; y[2] = -0.00003; z[2] = 8.;
   
   Double_t xmin = x[0], xmax = x[0];
   Double_t ymin = y[0], ymax = y[0];
   Double_t zmin = z[0], zmax = z[0];
   
   for (int i=1; i<3; i++) {
      if (x[i]<xmin) xmin = x[i];
      if (x[i]>xmax) xmax = x[i];
      if (y[i]<ymin) ymin = y[i];
      if (y[i]>ymax) ymax = y[i];
      if (z[i]<zmin) zmin = z[i];
      if (z[i]>zmax) zmax = z[i];
   }

   Double_t eps = 0.005;
   
   TH2F *h = new TH2F("h","h",10,xmin-eps,xmax+eps,
                              10,ymin-eps,ymax+eps);
   h->SetMinimum(zmin-eps);
   h->SetMaximum(zmax+eps);
   
   TGraph2D *gr = new TGraph2D(3,x,y,z);
   gr->SetMarkerStyle(21);

   h->Draw("Lego");

   gr->Draw(" PCOL SAME");
  
   h->GetXaxis()->SetTitle("x axis");
   h->GetYaxis()->SetTitle("y axis");
   h->GetZaxis()->SetTitle("z axis");
}
8

Thanks a lot for this workaround!

For reference: Values for theta and phi seem to be:

[code] // xz
canvas->SetTheta(0);
canvas->SetPhi(0);

// yz
canvas->SetTheta(0);
canvas->SetPhi(-90);

// xy
canvas->SetTheta(90);
canvas->SetPhi(0);
[/code]
Cheers,
Bjorn

9

an other possible way:

{
   Double_t x[3], y[3], z[3];
   x[0] = -0.01000; y[0] =  1.00000; z[0] = 9.;
   x[1] = -0.00005; y[1] = -0.00002; z[1] = 7.;
   x[2] = -0.00009; y[2] = -0.00003; z[2] = 8.;
   TGraph2D *gr = new TGraph2D(3,x,y,z);
   gr->SetMarkerStyle(21);
   gr->SetMargin(0.2);
   gr->Draw(" PCOL ");
}