Motivated by the needs of WSNs with ubiquitous structure such as the strip networks deployed in the Great Wall or pipelines, we present a lightweight geographic opportunistic routing approach to cope with the routing problem in complicated strip network. By carefully taking into account both the geographic information and the transmission direction, we propose the Virtual Plane Mirror (VPM) algorithm, which is inspired by the light propagation to select forwarding candidate with a short path. Two implementation problems of VPM, transmission spread angle and the communication range, are thoroughly analyzed based on the percolation theory. Based on VPM, we propose a geographic opportunistic routing strategy (LIPS). Experimental results show that the transmission successful rate of LIPS is 26.37% higher than the state-of-the-art approach, and the communication overhead and energy consumption rate are 33.11% and 40.23% lower, respectively. Furthermore, the path length in LIPS is close to the shortest