BEV size must be square

[GYJamor]

Hi, here is the details. when bev voxel is not a square, the VT-transform with ring&ray method still work？ mainly about the step to simplify FLOPs in VT. cause i see the Comment in get_proj_mat
bev_size = int(self.voxel_num[0]) # only consider square BEV
thank you