Any tech report about the anchor change operation?

[FengyuGuo]

https://github.com/rpng/open_vins/blob/4534a2f32d4763bdc8c95121b3292c7423e12aca/ov_msckf/src/update/UpdaterSLAM.cpp#L505

Any technical document about the anchor change operation and the state and covariance update process?

[goldbattle]

Not currently, we should probably expand the function comments. The code transforms the points from the oldest from into the newest frame. The core equation relation can be seen in this comment: https://github.com/rpng/open_vins/blob/4534a2f32d4763bdc8c95121b3292c7423e12aca/ov_msckf/src/update/UpdaterSLAM.cpp#L614-L615

This is the mapping between the old feature, to the new feature error state, which is used to propagate the covariance (the mean of the feature is straightforward to do).