oblique incidence in FDTD

hi
i am writing a code for FDTD technique.i need to have an oblique plane wave.i have read taflove 's book on FDTD. But

1)i would not understand the look up table method for incident wave.There are some equations regarding the geometrical interpretation of the method.What is the meaning
of it.Should i use those equations in my code

2)To calculate Einc and Hinc ,numerical phase velocity at an angle is required.
To calculate numerical phase velocity for any angle ,newton's method has been proposed in the fourth chapter.But i should start the newton's method with a initial guess.I cannot figure out what should be the initial guess.

Thanks

1) Theoretically speaking, you do not need the lookup table. It is used only to speed up the code. In inc/spr method, you set the field in the border of the cubic that you want the wave to be. However, as the wave is a uniform plane wave, you can think of it using a lookup table. You define the phase/amplitude at each point and translates/rotates these points to the border of the cubic space.

2) i don't remember. sorry.

hi
thank u so much for the reply
but i don't understand how to translate/rotate the points to the cube