TPolyLine3D with log scale

[ksmith]

Just another issue with visualization in ROOT in log space. Here is an alternate solution:

void testTPolyLine3D(){
  TCanvas* canvas = new TCanvas("canvas");
  canvas->SetLogz();

  TF2 *f2 = new TF2("myfunc","pow(10, x)",0,5,0,5);
  f2->SetMinimum(1E0);
  f2->SetMaximum(1E3);
  f2->Draw("surf");

  TPolyLine3D *l = new TPolyLine3D(2);

  l->SetLineWidth(5);

  l->SetPoint(0,0,0,log10(1E0));
  l->SetPoint(1,1,0,log10(1E1));
  l->SetPoint(2,2,0,log10(1E2));
  l->SetPoint(3,3,0,log10(1E3));

  l->Draw("same");
}

Other issues with log space include:

TCutG Plotted on Log Axis

I recently discovered that TCutG objects are always plotted as straight lines connecting points even if on a log axis. This can lead to misleading cuts. Say I draw a nice and square box around my data that happens to be exponential and plotted on a log plot and then use that cut to only look at that data. The result is not what one would expect as the cut needs to be evaluated against the data in linear space due to the plotting. Below is an example where I created a cut around the data in the …

GetUymax has problems with log scale

Dear ROOTers, I have this annoying problem with the Pad axis limits command, GetUymax(). When I want to plot a vertical line on a plot, I normally do like this: histo->Draw(); c1->Update(); TLine *l = new TLine(0.5,c1->GetUymin(),0.5,c1->GetUymax()); l->Draw(); This works very well for plots with a linear y scale. However, when I want to use a log scale, I observed the following: If I add the following line before the code above, I get a tiny line, for which Uymax is too small (Uymin looks o…