For applications in agriculture, sensors are often placed at grid points. Which grid (or pattern) minimizes the number of sensors and reach the full (area) coverage? It is not hard to show that the optimal solution is the triangle grid such that each cell is an equilateral triangle. However, when the requirement is the full coverage together with others, such as k-connectivity, the optimal solution would be nontrivial. Actually, there exist a lot of research efforts along this direction in the literature.