Making the both axes square on the pad

ROOT
1

Hi,

Is there a way to force TH2 to draw with both axes the same length? Or more importantly same scale? I’m trying to draw a TH2F where the axes are both in the same units and I’d like it to print that way. Trouble is, I also adjust the pad margins and this seems to affect the overall length of one axis relative to the other.

Thanks,
Bob

2

Yes, of course, if you change the margins the plot may not be square any more. Can you send a small example showing what you thingk is wrong ?

3

Hi,

I’m attaching a script that just draws the pad with the same code that I use. I’ve removed the part that fills the histogram. The reason that I need to adjust the pad margins is because otherwise I lose the labels on the color axis. Is there a way to force the histogram to draw each axis to the same scale regardless of what is done to the pad?

Thanks,
Robert
test.C (1.8 KB)

4

You can use gPad->SetFixedAspectRatio();

5

Hi Again,

So gPad is the global pointer to the current active pad. I have mulitple canvases open, so I figured that since TCanvas inherits from TPad I could use the TPad::SetFixedAspectRatio() on the canvas itself. For example:
{
TCanvas *c = new TCanvas(“c”,"",500,500);
c->SetFixedAspectRatio();
}
However, using gStyle->SetPadXXXMargin( ) still causes the aspect ratio to change between the x and y axes.

I’m also using root version 4.00/08 and do not have permission to upgrade (at least for the time being).

Thanks,
Robert

6

yes sorry you should do it on canvas

7

Hi,

I do it on the canvas, like I said above, and it still doesn’t work. I notice no difference between when I use it and when I don’t. Do I have to somehow grab the pad that’s in the canvas after the TH2F is drawn and set it then? If so, what’s the easiest way to do it?

Thanks,
Robert

8

With the following values in your macro you get a square:

  Float_t leftmargin  = 0.1;
  Float_t rightmargin = 0.12;
  Float_t topmargin   = 0.045;
9

Hi,

I dont want to have edit the margins to both get the color axis and to get the x-y axes square.

When I dump the TCanvas object I find that these are the values I would like to change in my script. The methods TCanvas::GetX1(), etc., return me these values.

fX1 -1.40755 X of lower X coordinate
fY1 -1.59144 Y of lower Y coordinate
fX2 1.36981 X of upper X coordinate
fY2 1.1323 Y of upper Y coordinate

To change these values I’ve found that TPad::Range(x1,y1,x2,y2) works; however, I can’t figureout how to make the histogram adjust to these new settings. TPad::RangeChanged(), Update(), and Draw() seem to do nothing.

Thanks,
Robert

10

see the short example below

[code]{
//method1. compute ymax to get a commensurate range
// 1 pixel must correspond to the same range in x and y
TCanvas c1(“c1”,“c1”,10,10,800,600);
Float_t xmin = 0;
Float_t xmax = 20;
Float_t ymin = -2;
Int_t npx = gPad->GetWw();
Int_t npy = gPad->GetWh();
Float_t ymax = ymin + (xmax-xmin)*npy/npx;
TH2F h(“h”,"",20,xmin,xmax,20,ymin,ymax);
h.Draw();
TArc a1(6,4,6);
a1.Draw();

//method2. set a square virtual canvas size in a non-square canvas
TCanvas c2(“c2”,“c2”,200,50,800,600);
c2.SetCanvasSize(700,700);
c2.DrawFrame(0,0,20,20);
TArc a2(10,10,10);
a2.Draw();
}
[/code]

Rene

11

Hi,

Method 2 works if I dont adjust the pad margins. See attached for an extreme example. Trouble is, I would like to adjust the pad margins, and have square axes without having to guess at their proportions everytime.

Thanks,
Robert
test.C (2.11 KB)