Key points are not available for this paper at this time.
Isophote comprises a locus of the surface points whose normal vectors make a constant angle with a fixed vector. Main objective of this paper is to find the axis of an isophote curve via its Darboux frame and afterwards to give some characterizations about isophote and its axis. Particularly, for isophotes lying on a canal surface will be obtained other characterizations again.
Doğan et al. (Thu,) studied this question.