Suggestion: different solints for antenna groups with different distances

[henedler]

I have a suggestion for a feature that might solve computation time and reduce the complexity of future LOFAR pipelines:
When solving for ionospheric effects in LOFAR data, the solutions of e.g. a core station vary on much longer time intervals compared to e.g. a distant remote or international station (with respect to some central reference station).
As a consequence, we can use much longer time intervals for those stations and prevent over-fitting. If one wants to do that with the current DP3, one needs to run multiple consecutive solves with different solints and either resetting or constraining the solutions for groups of stations - which costs time and also makes the pipelines more complicated to develop and maintain.

It would be handy if this could be a direct constraint in the solver, similar to the feature of having different solints for different directions. It would probably mean that the user has to define either different groups of stations (similar to the stationconstraint feature, [[CS001LBA..,],[RS307LBA,..]]) or, alternatively, groups with different distances to the central station [1km, 100km, 1000km...], which then get different solints: [16,4,1].
This could also be extended to frequency by using different smoothnessconstraints for different groups of stations (similar to the smoothnessrefdistance feature, but a bit more flexible).

I'm not sure if that is easy to implement, but it would be a nice-to-have.