calculate the length of scattered data

Hello everyone,

can anyone tell me how to calculate the length of the curve l plotted here?

thanks in advance!

Answer 1

[KSSV]

Let A be your n*2 data points

A = [A ; A(1,:)] ; 
x = A(:,1) ;   % x coordinates of the points 
y = A(:,2) ;   % y coordinates of the points 
iwant = sum(sqrt(diff(x).^2+diff(y).^2)) ;   % distance formula 

[Walter Roberson]

This assumes that the data is sorted, which we cannot assume for the case of scattered data, not even when the user has drawn a boundary line -- the drawing of the boundary line might have been a separate operation .

If we are given sorted points, then they are not scattered ;-)

If they are scattered, then we need to do something like boundary() to find the point ordering. There are also sorting techniques based on angle from the centroid.

Note: I do not see where you have closed the curve back to the first point ?

[KSSV]

Yes you are right....Walter. Edited the code considering your Note.

[yunwei hu]

Sorry l did not explain clearly before.

Actually this is the contour of a cell and i would need the length of it. That is why the curve is closed.

[KSSV]

If plot(x,y), give you the above curve..you can use what I have given.