Algorithm 1 Camera view selection.

Input: The complete trajectory ${\mathbf{T}}^n=\left\{{\mathbf{T}}_i\right\},i\in [1,n]$; the list of loop closure key frames $\mathbf{L}=\left\{j\right\},j\in [1,l]$.

Output: The reduced trajectory ${\mathbf{T}}^r=\left\{{\mathbf{T}}_k\right\},k\in [1,r]$. 1:for each input frame $i\in [1,n]$ do 2:    Compute ${\alpha }_i$, ${\beta }_i$, ${\gamma }_i$, ${\mathbf{v}}_i$; 3:    if ($|{\alpha }_i|\le T{h}_{\alpha }$ or $|{\beta }_i|\le T{h}_{\beta }$ or $|{\gamma }_i|\le T{h}_{\gamma }$) and $\left|\right|{\mathbf{v}}_i\left|\right|\le T{h}_v$ then 4:        Prune away ${\mathbf{T}}_i$; 5:    else if $i\ne j$ then 6:        for each loop closure key frame $j\in [1,l]$ do 7:            Compute the con-visibility ratio ${\rho }_{i,j}$; 8:            if ${\rho }_{i,j}\ge T{h}_{\rho }$ then 9:                Prune away ${\mathbf{T}}_i$; 10:    else 11:        Save ${\mathbf{T}}_i$; 12:return The reduced trajectory ${\mathbf{T}}_k={\mathbf{T}}_i$;