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)

if it's not right please show me a way to extract direction features from my(x,y) coordinates series.

Thank you in advance