Hi,
@Serrof maybe if you change this line:
public SpacecraftState getInterpolatedState(AbsoluteDate date) { return spacecraftState; }
With something like:
public SpacecraftState getInterpolatedState(AbsoluteDate date) { return spacecraftState.shiftedBy(date.durationFrom(spacecraftState.getDate())); }
It will work like before no?
I’m not sure about the public boolean isForward() { return true; } though.
@luc I know you"re not happy with using “shiftedBys” but we already have had two questions on this new API. I understand Orekit should be as accurate as possible but it should also be accessible to users 
We did cope with “shiftedBy” for years in the OD and the measurement generation, so why not add a default method in the MeasurementBuilder interface that would allow the old code to work?
It would look like this (Not sure about all the methods in the interpolator, I haven’t thought this through very much).
/** Generate a single measurement.<p>
*
* Warning: This method uses "shiftedBy" so it is not as accurate as the method above that uses interpolators.
*
* @param states all spacecraft states (i.e. including ones that may not be relevant for the current builder)
* @return generated measurement
*/
default T build(AbsoluteDate date, SpacecraftState[] states) {
final Map<ObservableSatellite, OrekitStepInterpolator> interpolators = new ConcurrentHashMap<>();
for (int i = 0; i < states.length; i++) {
final ObservableSatellite sat = getSatellites()[i];
final SpacecraftState state = states[i];
final OrekitStepInterpolator interpolator = new OrekitStepInterpolator() {
public OrekitStepInterpolator restrictStep(SpacecraftState newPreviousState, SpacecraftState newCurrentState) { return null; }
public boolean isPreviousStateInterpolated() { return false; }
public boolean isForward() { return true; }
public boolean isCurrentStateInterpolated() { return false; }
public SpacecraftState getPreviousState() { return state; }
public SpacecraftState getInterpolatedState(AbsoluteDate date) { return state.shiftedBy(date.durationFrom(state.getDate())); }
public SpacecraftState getCurrentState() { return state; }
};
interpolators.put(sat, interpolator);
}
return build( date, interpolators);
}
What do you think?