Directional feature extraction and Freeman chain code

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aurora 2012-10-31

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https://ww2.mathworks.cn/matlabcentral/answers/52447-directional-feature-extraction-and-freeman-chain-code

Hi,

I used a freeman chain code file - that's exchanged by Alessandro Minnini- to extract the features of my (x,y) coordinate series and I'm new to this algorithm and matlab too.

I've the following questions :

1- When I run it on my data an error sometimes occurs : " Curve isn't 8-connected in elements " , why ?

2- The cc.code length is np-by-1 or 1-by-np array and most of its numbers is repeated, so can we reduce the result to only get the features of a character without duplicates and avoiding a feature vector length as the original coordinates length ?

3- if I used the following code to get the directions of a series of coordinates or the angles , is it right?

deltax=x(1:end-1)-x(2:end);
deltay=y(1:end-1)-y(2:end);
deltas=sqrt(deltax.^2+deltay.^2);
ax= deltax(1:end)./deltas(1:end); thx=cos(ax);
ay= deltay(1:end)./deltas(1:end); thy=sin(ax);
tangent=ay./ax;
theta=atan(tangent)