Fig. 6.

Effect of $d$ and $\theta$ on vessel visibility. (a) When the distance $d$ from a starting point changes and there is no change in $\theta$, the original field-of-view remains the same. (b) When there is a change in $\theta$ and a small change in $d$, there is some overlap in the field-of-view. Larger changes in $\theta$ would cause less overlap. (c) When there is a large change in $d$ and $\theta$ combined, there is a significant change in the field-of-view.