Fig. 6
From: Geographical model-derived grid-based directional routing for massively dense WSNs
Routing direction and routing paths. Here, the sinks indicated by circles are located at 
and 
, and the black regions represent the holes. a Routing direction \(\widetilde {\mathbf {u_{f}}}\). b Routing paths: the source is close to the grid point 
. c Routing paths: the source is close to the grid point 