Where is the code for estimating 3D translation and rotation?

[Taeuk-Jang]

Hi,
I am new to tensorflow, and I only can find VGG16 as a backbone.
Where can I find the code for calculating center of the segmented objects and translation, and rotation etc?
And from the paper, it says normalized ray pointing to center of object has 3 dimensions, (n_x,n_y,T_z).
How do you get T_z with (x,y)?

Thank you