Coordinate conversion library

Collaboration diagram for Coordinate conversion library:

Modules
	Coordinate conversion constants
	Coordinate conversion typedefs
	Coordinate conversion functions

Detailed Description

Coordinate conversion.

COSMOS supports a wide variety of coordinate systems for both position and attitude. This library provides both definitions of structures for representing these various systems, as well as functions for conversion between them. A number of constants are also defined that relate to the various physical parameters involved in these conversions.

COSMOS approaches the process of defining position and attitude by defining something called a Location. A fully defined Location, stored in a locstruc, represents the complete state vector for an object, including time, represented in all possible coordinate systems. This Location is first broken down in to a posstruc and attstruc, representing Position and Attitude. These are subsequently broken down in to the various possible representations in the various systems supported.

Position is actually a triple of the 0th, 1st and 2nd derivative of position, measured in either meters, or meters and radians, with respect to a standardly defined coordinate system. The systems currently supported are:

• Barycentric: Cartesian, ICRF centered on Solar System Barycenter
• Earth Centered Inertial: Cartesian, ICRF centered on instantaneous Earth position
• Selene Centered Inertial: Cartesian, ICRF centered on instantaneous Moon position
• Geocentric: Cartesian, ITRF centered on instantaneous Earth position
• Selenocentric: Cartesian, lunar pole and equator of epoch and the IAU node of epoch centered on instantaneous Moon position
• Geodetic: Oblate Spherical, ITRF centered on instantaneous Earth position
• Selenographic: Spherical, lunar pole and equator of epoch and the IAU node of epoch
• Geospherical: Spherical, ITRF centered on instantaneous Earth position

The posstruc also contains some extra derivative information such as:

• angular separation between Earth and Sun
• angular separation between Moon and Sun
• angular size of Sun
• Solar radiance
• Sun to Earth vector
• Sun to Moon vector

Attitude is also a triple of the 0th, 1st and 2nd derivatives. The 1st and 2nd derivatives, or Omega and Alpha, are represented as vectors in the relevant coordinate system. The 0th derivative is represented as the quaternion that will transform a vector in the relevant coordinate system into a vector in the body frame. The systems currently supported are:

• Topocentric: Geocentric based, East North Up
• Local Vertical Local Horizontal: Geocentric based, +z = -position, +y = +z cross velocity, +x = +y cross +z
• Geocentric: Geocentric based
• Selenocentric:: Selenocentric based
• ICRF: ICRF based

Additionally, support is provided for Two Line Element and table based coordinates.