## angle and radius of a curve

### joo (view profile)

on 17 Nov 2012
Accepted Answer by John Petersen

### John Petersen (view profile)

i have the xy data (in excel) to obtain the following curve in black (obtained in laboratory)

` there anyway to obtain the parameters in red, or something similar to it? i have many curves like those and i need to classificate them by some parameters ans this were the ones i remembered`

any help of code or theorical would be very good to me. thank you so much.

here you have the excel data and the plots (there are two types, but the parameters i want are as well the angle and radius).

` you very much guys.`

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### John Petersen (view profile)

Answer by John Petersen

### John Petersen (view profile)

on 20 Nov 2012

It would help if you gave some definitions, but I'll do that, hopefully correctly interpreting your question.

Define the curve as C = [xv,yv] where xv and yv are a vector of corresponding points of the curve. Then the red X can be defined as

```X = [xv(1),yv(end)];  % this may not work for the general case, but
%should work for the curve you've shown if the curve starts at the left
%and moves to the right.
v1 = (X-C(1,:));   %vector to starting point of the curve
v2 = (X-C(end,:)); %vector to ending point of the curve
Cangle = acos(dot(v1,v2)/(abs(v1)*abs(v2))); % curve angle
r1 = abs(v1);  % distance to starting point of curve
r2 = abs(v2);  % distance to ending point of curve
```

Image Analyst

### Image Analyst (view profile)

on 23 Nov 2012

John, did you get an advance copy of the Mind Reading Toolbox or something?

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