	Handling frames
	A simple model Frames known by JEphem Coordinate labels Here, we see the classes used to represent frames and deal with coordinate transformations.

A simple model

To be flexible, the program should be able to respond to a request like "I want the coordinate of this body in a frame materializing this reference system, having this center, this reference plane and this reference axis".
It should also possible to specify if we want geometrical or apparent coordinates ; if apparent coordinates are wanted, it should be possible to specify from where they are apparent.

For the first version, I simplified and developed JEphem to be just able to respond to "I want the coordinates in this frame", for frames currently used in astronomy. In JEphem API, to identify a frame, constants of interface jephem.astro.spacetime.SpaceConstants are used.
In fact, the notion of frame, as it is used in the API, corresponds to "a way to express the coordinates" : it includes (sometimes implicitely) the information about apparent / geometrical coordinates.

The frames known by JEphem

The API names are the constant names of jephem.astro.spacetime.SpaceConstants ; these names are use throughout the program to designate the different frames.

API name	Description	Names of the spherical coordinates (order : r, q, j)
FRAME_THEORY	The coordinates are expressed as given by the theory used to compute them, without any transformation. Center : depends on the theory Ref. plane : depends on the theory Ref. axis : depends on the theory Reference system : depends on the theory Geometric coordinates	Depends on the theory
FRAME_EC_HELIO_GEOMETRIC	Center : Sun Ref. plane : Mean ecliptic J2000 Ref. axis : Mean equinox J2000 Reference system : FK5 Geometric coordinates	(D, b, l)
FRAME_ECLIPTIC	Center : Earth Ref. plane : Mean ecliptic of date Ref. axis : True equinox J2000 Reference system : FK5 Apparent coordinates	(r, l, b)
FRAME_EQUATORIAL	Center : Earth Ref. plane : True Equator of date Ref. axis : True equinox J2000 Reference system : FK5 Apparent coordinates	(r, a, d)

A method, jephem.astro.spacetime.Space.getFrameLabel(int whichFrame) permits to get the English name of a given frame.

Coordinate labels

I developped constants and methods to identify the coordinates, and retrieve their names. This is implemented in classe jephem.astro.spacetime.Space and jephem.astro.spacetime.SpaceConstants.

Six constants (SpaceConstants.COORD_xx) permit to identyify a coordinate.

The notion of coord group was introduced for convenience (the groups are identified by SpaceConstants.COORDGROUP_XXX). Groups are accessed with Space.getCoordGroup(int frame, int sphereCart) This is useful to get the labels.

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