[Orekit Developers] Time-variable potential

[Tanguy Yannick <Yannick.Tanguy@cnes.fr>]

Hello,

We are implementing a terrestrial tides force model. This model computes a gravity field and needs to update C/S coefficients. Droziner and Cunningham models cannot be used because we want to calculate accelerations separately and at the moment, Droziner/Cunningham cannot update their coefficients during an extrapolation. So we had to duplicate some code, which is only a work-around...

By the way, some earth potential models propose periodic variations on the first terms of potential (see http://grgs.obs-mip.fr/index.php/fre/Donnees-scientifiques/Champ-de-gravite/grace/static).

So I think there is a need for time-variable potential, which could be used for both earth potential perturbations and tidal effects (terrestrial crust, oceans tides, etc.). 

There could be many ways to implement this, and we would like to propose a solution :
- Creating an interface for classes that can update some coefficients at a given date
- Creating an Abstract Cunningham (or Droziner) model which implement the computation of the acceleration
- The terrestrial tides force model could extend the Abstract Cunningham model and implement the new interface
- The existing Droziner and Cunningham models would simply inherit the abstract models
- A new class (TimeVariableCunninghamModel ?) could extend the abstract class and implement the new interface to handle periodic variations on the first term coefficients.

What do yo think about this ? 
Shall I open a ticket on JIRA now ?

Best regards,


Yannick TANGUY