Eclipsing and line of sight computations

[ChristopherRabotin]

High level description

Nyx can compute the eclipsing (with penumbra) and the line-of-sight visibility. This algorithm is derived in the MathSpec and its implementation is verified in the "GEO orbit raising" example.

ANISE needs to add this capability and verify that it (roughly) matches SPICE. The algorithm is probably different than that of SPICE, so one should expect to see small differences.

Requirements

• Compute the eclipsing state of one object given N other objects whose tri-axial ellipsoid is defined in the Almanac.

Test plans

• Move the tests from Nyx to ANISE
• Using SPICE's geometry finder, find the times of eclipse start and end, and ensure that the algorithm implemented in ANISE also returns eclipses during those times -- https://naif.jpl.nasa.gov/pub/naif/toolkit_docs/C/cspice/gfoclt_c.html

Design

The design should be identical to that in Nyx.

Algorithm demonstration

MathSpec