Dividing matlab plot into grids - matlab

Question

I have two different functions of time x(t) and y(t). I want to plot x(t) vs y(t) in Matlab . The plot needs to be divided into a 40x40 grid stretching from min and max values of signal in each direction. I then need to calculate the number of grid boxes occupied in the plot. Please suggest a convenient way to implement this in Matlab.
I've tried the following code (neglect the upper and lower limits of axis):
NrGrid = 20; % Number Of Grids
x = linspace(0, 100, NrGrid+1);
[X,Y] = meshgrid(x);
figure(1)
plot(X,Y,'k')
hold on
plot(Y,X,'k')
hold off
set(gca, 'Box','off', 'XTick',[], 'YTick',[])
axis square
In my understanding, the code only divides the plot into grids. how do I count the number of grids that are occupied?
Reference: I basically need to implement the algorithm in this paper:
http://www.fhv.at/media/pdf/forschung/prozess-und-produktengineering/working-papers/working-papers-2005/detecting-ventricular

Answer 1

Sounds like you want to create a 40x40 matrix and then use a Bresenham line drawing algorithm to connect each of the points (after appropriate scaling) in x(t)/y(t) correspondence in that matrix.
You can then use nnz to count the number of non-zero elements in the matrix.

Answer 2

I managed to get a much simpler solution than the one mentioned by Dave Durbin by quantizing the signal into 40 levels and then comparing it with its shifted region. The code is attached for reference:
function TD=TimeDelay(val,fs)
n=40;
jump=( max(val) + abs(min(val)))/40;
level=zeros(n,1);
level(1)=min(val) + jump;
for i=2:n
level(i)=level(i-1)+jump;
end
level(n)=level(n)+1;
ScaledECG=zeros(size(val));
ScaledECG(val <= level(1))=1;
for j=2:n
ScaledECG( val<=level(j) & val>level(j-1))=j;
end
tau=fs*.5;
N=zeros(n,n);
for k=tau+1:1:length(val)
N(ScaledECG(k-tau),ScaledECG(k))=N(ScaledECG(k-tau),ScaledECG(k)) + 1;
end
N(N>5)=0;
N(N<=5)=1;
TD=sum(sum(N));