  Probability distribution for the ratio ($r$) of consecutive level spacings of
the eigenvalues of a Poisson (generating regular spectra) spectrum and that of
a GOE random matrix ensemble are given recently. Going beyond these, for the
ensemble generated by the Hamiltonian $H_\lambda = (H_0+\lambda
V)/\sqrt{1+\lambda^2}$ interpolating Poisson ($\lambda=0$) and GOE ($\lambda
\rightarrow \infty$) we have analyzed the transition curves for $\langle
r\rangle$ and $\langle \tilde{r}\rangle$ as $\lambda$ changes from $0$ to
$\infty$; $\tilde{r} = min(r,1/r)$. Here, $V$ is a GOE ensemble of real
symmetric $d \times d$ matrices and $H_0$ is a diagonal matrix with a Gaussian
distribution (with mean equal to zero) for the diagonal matrix elements;
spectral variance generated by $H_0$ is assumed to be same as the one generated
by $V$. Varying $d$ from 300 to 1000, it is shown that the transition parameter
is $\Lambda \sim \lambda^2\,d$, i.e. the $\langle r\rangle$ vs $\lambda$
(similarly for $\langle \tilde{r}\rangle$ vs $\lambda$) curves for different
$d$'s merge to a single curve when this is considered as a function of
$\Lambda$. Numerically, it is also found that this transition curve generates a
mapping to a $3 \times 3$ Poisson to GOE random matrix ensemble. Example for
Poisson to GOE transition from a one dimensional interacting spin-1/2 chain is
presented.
