Question Re: Canvas and Axis Aspect Ratios

[jfcaron]

If I make a TCanvas with one of the “form” constructors that gives a 500x500 pixel canvas (or if I manually make one with the same width and height), and the X and Y axis ranges are equal (say -1 to 1), then does the area of the graph have a 1:1 aspect ratio like the canvas?

I.e. are the left, right, top, and bottom margins automatically equal in pixel width by default? I would like some way to ensure that the axes of the plot have a fixed aspect (in my case I require 1:1), but I am not sure if this aspect is always the same as the canvas aspect.

Thanks for any clarifications,
Jean-François

[couet]

The size you specified when you create a TCanvas take into account the windows decoration also.
See the comment here: root.cern.ch/root/html534/TCanvas.html

At creation time, the canvas size defines the size of the canvas window (including the window manager’s decoration). To define precisely the graphics area size of a canvas, the following four lines of code should be used:

{
Double_t w = 600;
Double_t h = 600;
TCanvas * c1 = new TCanvas(“c”, “c”, w, h);
c->SetWindowSize(w + (w - c->GetWw()), h + (h - c->GetWh()));
}

[ferhue]

With the code above, the axes aspect ratio is not exactly the same as the canvas aspect ratio (even after subtracting borders).

For setting exact axes aspect ratio setting, see this post

Set real aspect ratio of TH2 or TGraph

This is a follow-up op Resize canvas to get real aspect ratio of TH2 or TGraph When you have a TH2, TGraph or TGraph2D where your x and y axes are in the same units (e.g. both MeV, or both mm, or both in ns), you normally want to get a real aspect ratio in your monitor or canvas. In other words, you want that the unit length of each axis occupies the same number of pixels, so that the representation on your monitor is proportional to reality and not distorted. I wrote a simple function to acco…