How to convert gazebo world to octomap?

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I understand converting a gazebo world to a voxel map/octomap isn't supported by gazebo, but is there a way to indirectly accomplish this? The easiest way I could imagine is to make some sort of global sensor (which may not be possible), or alternatively, add a number of sensors to the environment with infinite spherical views that will capture most of the environment. Then I'd use the distance measurement outputs to create an octomap. Does anyone have any other, perhaps simpler, suggestions?