[Orekit Developers] TimeStamped PVCoordinates/AngularCoordinates

[MAISONOBE Luc <luc.maisonobe@c-s.fr>]

Hi all,

One of the lowest level data structure we use extensively in Orekit is  
PVCoordinates. It simply holds two vectors and thats all. The class  
was not intended to be used alone, as people most often need to  
associate it with both time (typically either an AbsoluteDate instance  
of an offset from some reference) and a Frame instance. When these  
more complete data are needed, we use slightly higher level objects,  
like CartesianOrbit for example. Another similar structure is  
AngularCoordinates, all the discussion below applies to both cases.

However, I wonder if another intermediate level would be useful or  
not, with the date already associated with the two vectors (or  
rotation), but still without frames? There are several places in  
Orekit where this intermediate level is used, but up to now we relied  
simply on Pair<AbsoluteDate, PVCoordinates>, using the Pair<K,V> class  
provided by Apache Commons Math. This is cumbersome, and it does not  
implement TimeStamped, thus preventing us to collect a bunch of  
instances in a TimeStempedCache. As we often deal with a full  
ephemeris of PVCoordinates were all elements have a different date but  
all are in the same frame, letting the frame out of this seems fair to  
me.

I can see several different ways to implement it:

 1a) new classes TimeStampedPVCoordinates, TimeStampedAngularCoordinates ...
 1b) internal classes : PVCoordinates.TimeStamped ...
 1c) changing current PVCoordinates to add time

I would personnally prefer 1a as it is simpler than 1b and allow to  
keep also non-dated PVCoordinates which are useful when the date is  
either not meaningful for constant positions or when it is in some  
upper level structure and could lead to some consistency problems if  
1c were chosen.

If time-stamped versions of these classes were available, we could  
also simplify the signature of the static interpolation methods (and  
probably move them to the new classes).


What do you think about a new class at this level?

best regards,
Luc

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