Gaussian filtering of Adcole Roundness data

Hi all,

I'm having trouble working through the examples in the book "Computational surface and roundness metrology". When attempting to run the following program, I get the following error. I'm trying to get my head around the line of S1(blah) = S. I don't understand how this can work but I've placed it in exactly as described in the book. Any help you give is greatly appreciated.

omegac = 20;                        % Cutoff in units of UPR (undulations per revolution)
n = 3600;                           % number of points measured (3600 = 0.1 of a degree)
alpha = sqrt(log(2)/pi);
i = (-n/omegac:1:n/omegac)';        %n/omegac is the number of points in one cutoff
x = i*omegac/n;
S = (omegac/alpha).*exp(-pi*(i.*omegac/alpha/n).^2);
S = S/sum(S);
plot(x,S)

q = (1:n)';
theta = (q-1)/n*2*pi;               % Generate angle data
R = sin(2*pi/n*omegac.*q);          % profile with UPR
% note that the variable R is used to indicate radial deviation data

% plot(theta,R)

S1(3600,1) = 0;                     % Generate an array with 3600 points
S1(1441:2161,1) = S;                % Centre filter in S1
Sf = fft(S1);                       % FFT of S1
Rf = fft(R);                        % FFT of R
wf = Sf.*Rf;                        % term by term multiplication
w = ifft(wf);                       % inverse FFT of wf
w = [w(1801:3600,1);w(1:1800,1)];
plot(theta,R,'b-',theta,w ,'r-')

radius = 20;                         %Enter the radius of the polar plot)
polar(theta, R + radius)
hold on;
polar(theta,w + radius, 'r-')

ERROR

Subscripted assignment dimension mismatch.
Error in gauss_test2 (line 25)
S1(1441:2161,1) = S;                % Centre filter in S1

I'd like to input 3600 point data from my Adcole and apply a Gaussian filter to the FFT with certain UPR settings then convert back to the time domain.

Any advice or examples?

[Stephen23]

Advice: you should not use i or j as variables names, as these are the names of the inbuilt imaginary unit . You might need a complex number one day, and then it is a real pain because you have redefined those variables.

Answer 1

[Star Strider]

The S vector is a (361x1) double array and the subscript range [1441:2161] is 721.

That mismatch is throwing the error.

I’m not sure what you’re doing, so I can’t suggest a fix other than to define the subscript range as [1441:1441+length(S)-1] or create S to be a (721x1) vector.