Getting coordinates through comparing .pgm files using opencv

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1 - Generated the .pgm files through gmapping using LIDAR data.

-- One with partial map

-- One with map of the whole area

Trying to:

2 - Use opencv to compare the maps

3 - To get the coordinates of the lidar at the partial map

-- For pinpointing this lidar in the full map

Above is the brief summary of the problem encountered. Anyone may have any advice or a direct solution.

Please and Thank You viewers.