Let g be an affine Lie
algebra and gL its Langlands dual. It was conjectured by Kashiwara, Nakashima, and
Okado that g has a positive geometric crystal whose ultra-discretization is isomorphic
to the limit of certain coherent family of perfect crystals for gL. We prove that the
ultra-discretization of the positive geometric crystal for g = D4(3) given by
Igarashi and Nakashima is isomorphic to the limit of the coherent family
of perfect crystals for gL= G2(1) constructed by Misra, Mohamad, and
Okado.