Why does histogram data from hist3 have to be transposed?

I just learnt how to use hist3 and I don't understand a couple of lines in the example code that Matlab help provided. I've copy pasted the example for plotting a density histogram with intensity map (an intensity map is what I'm interested in plotting actually). The two lines that I don't understand are: 1. n1 = n'; --> why does the histogram have to be transposed? 2. h.ZData = ones(size(n1)) * -max(max(n)); --> what does this line do?

%Load the sample data.

load seamount

%Correct grid for negative y-values and draw histogram in 2D.

hold on

dat = [-y,x];

hist3(dat)

%Extract histogram data.

n = hist3(dat);  % default is to 10x10 bins

n1 = n';

n1(size(n,1) + 1, size(n,2) + 1) = 0;

%Generate grid for 2-D projected view of intensities.

xb = linspace(min(dat(:,1)),max(dat(:,1)),size(n,1)+1);

yb = linspace(min(dat(:,2)),max(dat(:,2)),size(n,1)+1);

%Make a pseudocolor plot.

h = pcolor(xb,yb,n1);

h.ZData = ones(size(n1)) * -max(max(n));

colormap(hot) % heat map

title('Seamount:Data Point Density Histogram and Intensity Map');

grid on

view(3);

Answer 1

[Thorsten]

1. 1. n1 = n'; --> why does the histogram have to be transposed?

Because dat is defined as

 dat = [-y, x]

but the grid is defined with xb from the first column (that is -y) and yb from the second column of dat, which is x:

 xb = linspace(min(dat(:,1)),max(dat(:,1)),size(n,1)+1);
 yb = linspace(min(dat(:,2)),max(dat(:,2)),size(n,1)+1);

To get the right mapping for the x and y axis in the plot

h = pcolor(xb,yb,n1);

the n1 has to be transposed before.

2. h.ZData = ones(size(n1)) * -max(max(n)); --> what does this line do?

This moves the pcolor plot down by max(max(n) to appear below the hist3 plot.

[lalikesbrains]

That makes sense, thank you! :)