Logging the obstacle surrounding the grid data to a file.

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Hello.

I have implemented A, Dijkstra and GBFS algorithm for path planning in a single robot. I have used costmap2D for the process. I wish to make a 33 or a 5*5 grid around the robot, which moves in the same way as the robot moves so that we have a tumbling window sort of process where we are able to detect the obstacle (mapping is already done, and obstacle is represented by value greater than 100 but less than 255)

How can I implement such a process in rospy, the output log can be either in CSV/JSON/XML?