When getting data measurements, we need to make sure that the measurement we are taking now is of the same thing we are measuring right before.
IE. GPS satellite measurement is coming from the same satellite as before
External Data Association is where the data is being associated before it is being considered in our state estimator.
- GPS, Visual Feature Matching, (loop closure detection, feature-based initial alignment), Apriltags
Internal Data Association is where data is being associating while inside our state estimator
- only the measurements/model are used to do data association
- ICP is one of them, as it relies on a good initial guess AND it solve association and state optimization together