# Bin navigation and assignment for TH3D

Hi. I’m trying to retrieve information from a 3D histogram and getting confused with the output.

So I’m using the code below to generate a 2x2x2 histogram and fill one of the bins positioned at (0,1,0) with 1.
To output the contents (included below) I get the number of bins (64 due to overflow in this case) and output the centre position and content of the bins.
But the bin with the value of 1 returns a position of (40.5, 41.5, 40.5) instead of somewhere close to (0,1,0). Also I would of expected the maximum range to be 3 from overflow not 63.5.

Can someone explain how the positions are assigned for TH3D?

Thanks!

{
int noBins3Dx = 2;
int noBins3Dy = 2;
int noBins3Dz = 2;

double min3Dx = -1.;
double max3Dx = 1.;
double min3Dy = 0;
double max3Dy = 2.;
double min3Dz = -1.;
double max3Dz = 1.;

TH3D* edep3D = new TH3D("e1", "edep3D", noBins3Dx, min3Dx, max3Dx, noBins3Dy, min3Dy,max3Dy, noBins3Dz, min3Dz, max3Dz);
double value = 1;
edep3D->Fill(0.,1.,0.,value);

int noOfBins = edep3D->GetSize();
cout << "No of bins = " << noOfBins << endl;
for (int i = 1; i <= noOfBins; i++)
{
cout  << edep3D->GetXaxis()->GetBinCenter(i)<< "\t" << edep3D->GetYaxis()->GetBinCenter(i) << "\t" <<edep3D->GetZaxis()->GetBinCenter(i) << "\t" << edep3D->GetBinContent(i) << endl;
}
}
-0.5    0.5     -0.5    0
0.5     1.5     0.5     0
1.5     2.5     1.5     0
2.5     3.5     2.5     0
3.5     4.5     3.5     0
4.5     5.5     4.5     0
5.5     6.5     5.5     0
6.5     7.5     6.5     0
7.5     8.5     7.5     0
8.5     9.5     8.5     0
9.5     10.5    9.5     0
10.5    11.5    10.5    0
11.5    12.5    11.5    0
12.5    13.5    12.5    0
13.5    14.5    13.5    0
14.5    15.5    14.5    0
15.5    16.5    15.5    0
16.5    17.5    16.5    0
17.5    18.5    17.5    0
18.5    19.5    18.5    0
19.5    20.5    19.5    0
20.5    21.5    20.5    0
21.5    22.5    21.5    0
22.5    23.5    22.5    0
23.5    24.5    23.5    0
24.5    25.5    24.5    0
25.5    26.5    25.5    0
26.5    27.5    26.5    0
27.5    28.5    27.5    0
28.5    29.5    28.5    0
29.5    30.5    29.5    0
30.5    31.5    30.5    0
31.5    32.5    31.5    0
32.5    33.5    32.5    0
33.5    34.5    33.5    0
34.5    35.5    34.5    0
35.5    36.5    35.5    0
36.5    37.5    36.5    0
37.5    38.5    37.5    0
38.5    39.5    38.5    0
39.5    40.5    39.5    0
40.5    41.5    40.5    1
41.5    42.5    41.5    0
42.5    43.5    42.5    0
43.5    44.5    43.5    0
44.5    45.5    44.5    0
45.5    46.5    45.5    0
46.5    47.5    46.5    0
47.5    48.5    47.5    0
48.5    49.5    48.5    0
49.5    50.5    49.5    0
50.5    51.5    50.5    0
51.5    52.5    51.5    0
52.5    53.5    52.5    0
53.5    54.5    53.5    0
54.5    55.5    54.5    0
55.5    56.5    55.5    0
56.5    57.5    56.5    0
57.5    58.5    57.5    0
58.5    59.5    58.5    0
59.5    60.5    59.5    0
60.5    61.5    60.5    0
61.5    62.5    61.5    0
62.5    63.5    62.5    0

Search for “global bin” in the TH1 class reference.

Ohh I see… Thanks!