Why we need to rot90 and flip the occupancy ground truth in LoadOccupancy?

[zhanghm1995]

Hi, I want to why we need to apply the below transformations in LoadOccupancy function?

# to BEVDet format
occupancy = occupancy.permute(2, 0, 1)  # to (16, 200, 200)
occupancy = torch.rot90(occupancy, 1, [1, 2])
occupancy = torch.flip(occupancy, [1])
occupancy = occupancy.permute(1, 2, 0)

Although the comment says they are used to transform the occupancy to BEVDet format, they are not exist in the BEVDet codebase.

Can anybody help to understand the purposes of these operations?

[Yzichen]

@zhanghm1995 I have this same question. Do you know the answer yet?

[zhanghm1995]

@Yzichen Sorry to reply so late. I still cannot understand these operations very well. It seems the built volume is different from the occupancy ground truth. However, the original BEVDet codebase doesn't need to do these operations, it is so weird.

[troylhy1991]

I guess it's related to align IMU coordinate with LiDAR coordinate.