A simultaneous robotic footprint and sensor coverage planning scheme is proposed to efficiently detect all the unknown targets with range sensors and cover the targets with the robot's footprint in a structured environment. The proposed online Sensor-based Complete Coverage (online SCC) planning minimizes the total traveling distance of the robot, guarantees the complete sensor coverage of the whole free space, and achieves near-optimal footprint coverage of all the targets. The planning strategy is applied to a crack-filling robotic prototype to detect and fill all the unknown cracks on ground surfaces. Simulation and experimental results are presented that confirm the efficiency and effectiveness of the proposed online planning algorithm.