Table 2.

Most common coverage failures in wireless visual sensor networks.

Failure Condition	Impact in WVSNs
Coverage optimization	Faulty nodes are artificially produced due to a monitoring schedule or coverage optimization. The set of nodes selected depends on the way visual information is monitored by the application.
New monitoring requirements	Changing the monitoring requirements may alter the role of the visual sensor for the application.
Occlusion	Desired targets may not be viewed due to occlusion, making the affected source node unavailable.
Low-relevance monitoring	Mobile nodes may retrieve information of low relevance for the application. This may also happen with static sensors with dynamic FoV adjustment.
Low-quality monitoring	Environmental conditions or bad configuration and adjustment of the sensors' cameras may reduce the quality of the retrieved visual information.