Algorithm 3: 2D-to-3D framework for object localization
Input: Projections $\left\{Proj\left(V,\theta \right)|\theta \in \Theta \right\}$, threshold T
Initialization: $U_{3D}=zeros\left(L,W,H\right)$
Procedure Backward projection
for each $\theta \in \Theta$ do
$U_{2D}\left(\theta \right)=fasterRCNN\left(Proj\left(V,\theta \right)\right);$
$U_{3D}=U_{3D}+BP\left(U_{2D}\left(\theta \right)\right)$
end
$U_{3D}=1\left(U_{3D}>T\right)$;
Compute the set of object bounding boxes {v} from $U_{3D}$;
return {v}