How to save a 2dmap obtained from a topic published by octomap ??

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Octomap provides a projected 2d map through the topic "projected_map". I want to save this map. The map server is also running. So i remapped the topic in the octomap server launch file : <remap from="map" to="projected_map"/>

This info is given in the ros wiki: map (up to fuerte) / projected_map (since fuerte) (nav_msgs/OccupancyGrid)

Downprojected 2D occupancy map from the 3D map. Be sure to remap this topic if you have another 2D map server running. New / changed in octomap_mapping 0.4.4: The topic is now projected_map by default to avoid collisions with static 2D maps

I am able to visualise in rviz but when i try to save it :

rosrun map_server map_saver -f mapName

The default map is saved rather than the map from octomap.

Any suggestion what is wrong ??