Why does the pointpillars net not have voxelization operation at the beginning?

[chenrui17]

I am a begginer of 3D obejct detection, i compared some pointpillars relization from det3d , mmdetection3D and PointPillars(https://github.com/zhulf0804), such as:

mmdetection3d : voxelization -> PillarFeatureNet -> PointPillarsScatter -> SECONDFPN -> Anchor3DHead det3d: PillarFeatureNet -> PointPillarsScatter -> RPN -> MultiGroupHead PointPillars : voxelization -> PillarEncoder -> backbone...

and i found mmdetection3D repo's pointpillars net and paper's PointPillars both have voxelization operation, but det3d's pointpillars net is not. why ?