Comparing two PointClouds.

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I'm using octomap for my mapping, this publishes a PointCloud2 message that represents all the points in the current map.

So at a point in time t = 0 i have a PointCloud2 message with some points inside. At a later time t>0 this PointCloud2 message has more points ( map is bigger).

Is there any efficient way to compare those 2 PointCloud2 messages and generate a third PointCloud2 message that contains only the new points?

Resetting the map is not possible since i need it to have it for mapping/planning.