Project about 3D point density

I have a school project where we are given a 1000-column, 3-row Excel file and told to organize it into 'boxes' in three dimensions then concentrate the points into the most dense z-box for each box on the bottom (25 since I chose to make 5x5x5 boxes). I then have to make a surface out of my 25 density points. I have made three functions that mostly complete the problem.

Data='Data.xlsx';
num=xlsread(Data);
x=num(1:size(num),1);
y=num(1:size(num),2);
z=num(1:size(num),3);
minx=min(x);
miny=min(y);
minz=min(z);
maxx=max(x);
maxy=max(y);
maxz=max(z);
xinc=linspace(minx,maxx,6);
yinc=linspace(miny,maxy,6);
zinc=linspace(minz,maxz,6);

First one reads the file and gets basic info such as the minimum and maximum values.

incx=xinc(2)-xinc(1);
incy=yinc(2)-yinc(1);
incz=zinc(2)-zinc(1);
spaces=zeros(25,1);
grnd=zeros(25,5);
for i=1:size(num)
    m=ceil((num(i,1)-minx)/incx);
    if m==0
        m=1;
    elseif m==6
        m=5;
    end
    n=ceil((num(i,2)-miny)/incy);
    if n==0
        n=1;
    elseif n==6
        n=5;
    end
    p=ceil((num(i,3)-minz)/incz);
    if p==0
        p=1;
    elseif p==6
        p=5;
    end
    grnd(m+5*(n-1),p)=grnd(m+5*(n-1),p)+1;
end
for j=1:25
    [g h]=max(grnd(j,1:5));
    space(j,1)=h;
end

This one finds the density of points. I'm most worried about this as values at the absolute minimum or maximum would give values outside 1:5, so I set any 0 value to 1 and 6 values to 0. Seems dubious, but I couldn't think of another way to fix it. Let me know if this could cause problems and suggest ways to fix it.

xboxes=linspace(16.309,18.701,5);
yboxes=linspace(35.149,75.861,5);
zboxes=linspace(11.309,13.701,5);
for i=1:5
    for j=1:5
        plot3(x(i,1),y(j,1),z(space((i+5*(j-1)),1)))
        hold on
    end
end
grid on

This plots the 25 points I found. I've tested these functions and it works until now, but I can't figure out how to make a surface of the points without messing up my data. Once I can do that (and maybe optimize the second function), I'm done. Any suggestions? Thanks in advance. I have included the Excel file in this post.

[Image Analyst]

It sure would be a heck of a lot easier for people to help you if you attached 'Data.xlsx'.

[Matt]

Sorry, I thought I did. It should be there now.