I'm using Zhang's method to determine the 3D camera parameters from a set of images. When calculating extrinsic parameters for the third image, I get the following matrix.
$$ \begin{vmatrix} 0.9848432 & 0.1745697 & 0.1719238 & - 43.812298 \\ - 0.1734468 & 0.9833136 & - 0.1705526 & 49.196566 \\ 0.0002832 & 0.0005524 & 0.0000002 & 8870.6728 \\ \end{vmatrix} $$
After calculating the eigenvectors and the eigenvalues of the rotation matrix (the first three columns) I get the following results.
$$ \begin{vmatrix} 0.7082676 & 0.7082676 & - 0.1934891 \\ - 0.0034034 + 0.7059357i & - 0.0034034 - 0.7059357i & 0.1344372 \\ 0.0002637 + 0.0003496i & 0.0002637 - 0.0003496i & 0.9718481 \\ \end{vmatrix} $$
$$ \begin{vmatrix} 0.9840684 + 0.1740798i & 0 & 0 \\ 0 & 0.9840684 - 0.1740798i & 0 \\ 0 & 0 & 0.0000202 \\ \end{vmatrix} $$
As far as I know, when I get purely real eigenvectors and eigenvalues, the eigenvector associated to $\lambda = 1$ will be the rotation axis (so far that has worked out fine) but when I get complex values I have no idea how to interpret them (I'm not very familiar with complex numbers).
I would really appreciate some help to determine the axis and angle of rotation from such results.