The usage of voxel format

[miaozhang97bosch]

Hello, Thanks for sharing this interesting work. I kind of wonder the meaning of using voxel rather than pillar in the radar encoding part. As I know, the radar point cloud of NuScenes doesn't really contain any real height information of the object, the z value of the point is actually derived from the relative pose of the radar sensor, which means you will only get one point at each certain (x,y) value, so in that case, if voxel is utilized, most of the voxel will be empty, since there is no point there. And also very limited 3d info can be extracted from that. I'll appreciate it if you can give me some hint about it or some ablation study of different encoding structures. Looking forward to your reply!