Bar3 plot with seperate x,y,height and width values - matlab

Question

Solution posted below function to plot bar 3 with separate x, y values and separate width and height values
bar3(x,y,z,xWidth,yWidth)
We are currently working on a project that allow one to visualize the area under a 3d function, f(x,y). The purpose of this is to demonstrate how the bars cut a 3d surface. Indirectly to visualize the desired integral.
We wish to have the bars match up with the intervals of the surface grid.
Below is a rough demonstration of the idea.
bar3 only has input for the x-values bar3(x,z), where as surf has a input for both the x and y surf(x,y,z)
Unfortunately this is what we are getting. - this is because bar3 cant be in terms of x and y
CODE:
clc;
cla;
d=eval(get(handles.edtOuterUpperB,'string'));
c=eval(get(handles.edtOuterLowerB,'string'));
b=eval(get(handles.edtInnerUpperB,'string'));
a=eval(get(handles.edtInnerLowerB,'string'));
n=eval(get(handles.edtInnerInterval,'string'));
m=eval(get(handles.edtOuterInterval,'string'));
h=(b-a)/n;
k=(d-c)/m;
[x,y] = meshgrid(a:h:b, c:k:d);
f=eval(get(handles.edtFunc,'string'));
surf(x,y,f);
hold on
bar3(f,1);

Answer 1

If you look closely, you will see that the XData and YData are different from the mesh to the 3D bar plot. This is because your mesh uses "real" x and y values while the bar plot uses indexes for the x and y values.
To fix this, you will want to change one or the other. For your case, the easiest one to change is going to be the surface. You can actually just omit the x and y inputs and the indexed x and y values will be used instead by default when generating the surface.
surf(f);
From the documentation for surf:
surf(Z) creates a three-dimensional shaded surface from the z components in matrix Z, using x = 1:n and y = 1:m, where [m,n] = size(Z). The height, Z, is a single-valued function defined over a geometrically rectangular grid. Z specifies the color data, as well as surface height, so color is proportional to surface height.
Update
If you want to keep the non-indexed values on the x and y axes, you will want to convert the bar3 plot instead. Unfortunately, MATLAB provides a way to specify the x axis bot not the y axis. You can take one of two approaches.
Change the XData
You can get the XData property of the resulting bar objects and change them to the data you want.
x = a:h:b;
y = c:k:d;
%// Anonymous function to scale things for us
scaler = #(vals)x(1) + ((vals-1) * (x(end) - x(1)) / (numel(x) - 1));
%// Create the bar plot
bars = bar3(y, f);
%// Change the XData
xdata = get(bars, 'XData');
xdata = cellfun(scaler, xdata, 'uni', 0);
set(bars, {'XData'}, xdata);
set(gca, 'xtick', x)
%// Now plot the surface
surf(x,y,f);
And just to demonstrate what this does:
x = linspace(0.5, 1.5, 5);
y = linspace(2.5, 4.5, 4);
f = rand(4,5);
scaler = #(vals)x(1) + ((vals-1) * (x(end) - x(1)) / (numel(x) - 1));
bars = bar3(y, f);
set(bars, {'XData'}, cellfun(scaler, get(bars, 'XData'), 'uni', 0))
set(gca, 'xtick', x)
axis tight
Change the XTickLabels
Instead of changing the actual data, you could simply change the values that are displayed to be what you want them to be rather than the indexed values.
x = a:h:b;
y = c:k:d;
labels = arrayfun(#(x)sprintf('%.2f', x), x, 'uni', 0);
bar3(y, f);
set(gca, 'xtick', 1:numel(x), 'xticklabels', labels);
hold on
%// Make sure to use the INDEX values for the x variable
surf(1:numel(x), y, f);

Answer 2

We found a user contributed function scatterbar3, which does what we want, in a different way than what bar3 uses:
http://www.mathworks.com/matlabcentral/fileexchange/1420-scatterbar3
There was however a slight hiccup that we had to correct:
hold on
scatterbar3(x,y,f,h);
scatterbar3 does not have separate inputs for the width and height of the bars, thus large gaps occur when the intervals do not equal one another. Demonstrated below.
We thus edited the scatterbar3 function in order to take both the width and height of the bars as inputs:
Edited scatterbar3 function:
function scatterbar3(X,Y,Z,widthx,widthy)
[r,c]=size(Z);
for j=1:r,
for k=1:c,
if ~isnan(Z(j,k))
drawbar(X(j,k),Y(j,k),Z(j,k),widthx/2,widthy/2)
end
end
end
zlim=[min(Z(:)) max(Z(:))];
if zlim(1)>0,zlim(1)=0;end
if zlim(2)<0,zlim(2)=0;end
axis([min(X(:))-widthx max(X(:))+widthx min(Y(:))-widthy max(Y(:))+widthy zlim])
caxis([min(Z(:)) max(Z(:))])
function drawbar(x,y,z,widthx,widthy)
h(1)=patch([-widthx -widthx widthx widthx]+x,[-widthy widthy widthy -widthy]+y,[0 0 0 0],'b');
h(2)=patch(widthx.*[-1 -1 1 1]+x,widthy.*[-1 -1 -1 -1]+y,z.*[0 1 1 0],'b');
h(3)=patch(widthx.*[-1 -1 -1 -1]+x,widthy.*[-1 -1 1 1]+y,z.*[0 1 1 0],'b');
h(4)=patch([-widthx -widthx widthx widthx]+x,[-widthy widthy widthy -widthy]+y,[z z z z],'b');
h(5)=patch(widthx.*[-1 -1 1 1]+x,widthy.*[1 1 1 1]+y,z.*[0 1 1 0],'b');
h(6)=patch(widthx.*[1 1 1 1]+x,widthy.*[-1 -1 1 1]+y,z.*[0 1 1 0],'b');
set(h,'facecolor','flat','FaceVertexCData',z)
Finally the working solution in action:
hold on
scatterbar3(x,y,f,h,k);