some concepts that not appear at paper

hello! thanks for your great works!

when i go into source code, i found "sweep", "ida" and "bda". these maybe something we have not seen in LSS. can you kindly explain the meaning of the three concepts? thanks!

--- update ---

sorry for my not familiar with nuscenes data. i google and found sweep images are not annotated intermediate frames (the counterpart of annotated keyframe). maybe the first sweep image (index 0 of sweep axis) in your code is keyframe. is that correct?
but i still not know about "ida" and "bda". hope you can kindly make some explanation for them. thanks!

for example in LSSFPN

def forward(self,
                sweep_imgs,
                mats_dict,
                timestamps=None,
                is_return_depth=False):
        """Forward function.

        Args:
            sweep_imgs(Tensor): Input images with shape of (B, num_sweeps,
                num_cameras, 3, H, W).
            mats_dict(dict):
                # ...
                ida_mats(Tensor): Transformation matrix for ida with
                    shape of (B, num_sweeps, num_cameras, 4, 4).
                # ...
                bda_mat(Tensor): Rotation matrix for bda with shape
                    of (B, 4, 4).
            # ...
        """
        batch_size, num_sweeps, num_cams, num_channels, img_height, \
            img_width = sweep_imgs.shape
        # ... ...

Start with LSSFPN.forward and the mats_dict docstring shown in the issue, then trace where sweep_imgs, ida_mats, and bda_mat are defined and used. Done means adding project documentation that explains sweep, ida, and bda, including the relationship between sweeps and keyframes, without requiring readers to infer their meanings from source code.