On the evolution of a rogue wave along the orthogonal direction of the ($t,x$)-plane

The localization characters of the first-order rogue wave (RW) solution $u$ of the Kundu-Eckhaus equation is studied in this paper. We discover a full process of the evolution for the contour line with height $c^2+d$ along the orthogonal direction of the ($t,x$)-plane for a first-order RW $|u|^2$: A point at height $9c^2$ generates a convex curve for $3c^2leq d<8c^2$, whereas it becomes a concave curve for $0<d<3c^2$, next it reduces to a hyperbola on asymptotic plane (i.e. equivalently $d=0$), and the two branches of the hyperbola become two separate convex curves when $-c^2<d<0$, and finally they reduce to two separate points at $d=-c^2$. Using the contour line method, the length, width, and area of the RW at height $c^2+d (0<d<8c^2)$ , i.e. above the asymptotic plane, are defined. We study the evolutions of three above-mentioned localization characters on $d$ through analytical and visual methods. The phase difference between the Kundu-Eckhaus and the nonlinear Schrodinger equation is also given by an explicit formula.