SimpleEci
Defined in: frame.rs:171
pub struct SimpleEciApproximate Earth-centered inertial frame: the “parent frame” for the ERA-only Z rotation used by the simple path. Ignores precession, nutation, polar motion, and frame bias.
Meeus ephemerides return Gcrs (the analytical “geocentric inertial”),
not SimpleEci. SimpleEci is specifically the complement of SimpleEcef
under the ERA-only rotation; there is no direct relationship between
SimpleEci and Gcrs other than both being Earth-centered inertial in the
broad Eci category.