Numerical feature system should allow heterogeneous features.

[tinevez]

In TrackMate 2, a spot feature can depend only on a spot feature. It cannot depend on an edge feature, because edges are always generated later, and their features are calculated once the spot features are already there.

This is why for instance a spot cannot have a feature that state to what track number it belongs to.

In TrackMate 3 we want the feature dependencies to be heterogenous, so that a spot feature can depend on anything.

This implies that there should be a way to deal with required features that are not here (for instance, you can compute the track a spot belongs to if the tracks have not been generated yet). This particular sub-issue is then probably linked to issue #1.

[tinevez]

This is fixed with the current revision. See for instance the dependency graph of the feature calculation:
https://github.com/fiji/TrackMate3/blob/master/src/main/java/org/mastodon/revised/model/feature/AbstractFeatureComputerService.java#L45-L77