I have read this paper. But i don't know what the Invariance means in page 3 and 5. Calculation/estimation of κ is NOT invariant and Invariant to viewpoint. What's the meaning of these sayings? When i read "Invariant to viewpoint", i think it means the k value is same when rotation and translation. But after i read "Calculation/estimation of κ is NOT invariant" ,i have no idea. Then i try the code what i got here,to caculate the k value.
And i have found that, the k value is different when shape have rotated which have the same sigma. Then i changed the sigma, k value is also different while the shape is same. When i set the sigma as 0.6667, the curvature of straight line is 1.6 not 0, why? The curvature of straight line should be zero,right? I don't why the value is 1.6. Then I tried to rotate the straight line, the curvature changed!!new value is -6.6. The papge said to find zero crossing to get concave-convex. But here curvature of straight line is not 0 is 1.6? Can somebody help me. Thank you very much!