Looking at the interface
EstimationModifier, I do not see any
Gradient implementation required.
Does this mean that they are used only for the value of the residual of an OD iteration, and not in the derivative information for the update?
The partial derivatives of the measurements with respect to estimated modifier’s parameters using
Gradient are internally computed inside the
modify method. You can for instance look at the class BaseRangeTroposphericDelayModifier.java which is extended by the RangeTroposphericDelayModifier.java.