storing 3d range data for localization

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It depends on your needs. 3D would provide would allow you to localize in a 3D space. However there are other considerations.

Firstly, localizing in the a 3D space would increase the complexity of the localization problem. It would thus impose a significant computation load on the system.

Secondly, it would also takes more memory just to store a 3D map as opposed to a 2D map. say you have 10 points for 1D, that would be 100 points for 2D and 1000 points for 3D.

Thirdly, the laser scanner only provides 2D data. So you might need to get a tilting mechanism to be able to build a 3d pointcloud. Or use other kind of sensors such as a kinect camera.

Most of the time when you are driving you just need to know your 2D location. It's nice to know what's your height with reference to AMSL; and you can install a fancy altimeter in your car. However you probably won't be looking at it much, simply because you don't really need the data.

So at the end of the day, it really depends on your needs.