gmapping with multiple lidars

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we have used a single lidar with slam-gmapping but now we want to extend this with multiple lidars (around 4 sick lidars). is there anyway to maybe merge the data together and continue using slam-gmapping (as ive read AMCL can subscribe to two LaserScan topics and combine it into one topic but would this be feasible).

otherwise is it advisable to have a gmapping node for each lidar and then combine the costmap created

Or alternatively use octomap to input all the data to one map and create a cost map

what would be the best approach?