//! Doppler shift computation.
//!
//! A satellite and a ground station move relative to each other, so the
//! frequency that arrives at the receiver differs from the frequency that
//! left the transmitter. This crate computes that shift from the relative
//! velocity.
//!
//! Two effects are present and they are separate. The classical shift is
//! proportional to the range rate divided by the speed of light, and it is
//! what a Doppler tracker compensates. The relativistic time dilation
//! between the two clocks is a second order correction that is far smaller
//! for orbital velocities, and it is offered separately so that a caller can
//! include it when the application needs it.
//!
//! The sign convention used here is that a positive range rate, meaning the
//! two terminals are moving apart, produces a negative shift and therefore a
//! lower received frequency. This matches the everyday observation that a
//! receding source sounds lower.
//!
//! ```
//! use apsis_doppler::{DopplerShift, range_rate_from_velocity};
//! use apsis_math::Vec3;
//!
//! // A satellite at the first axis moving away along it.
//! let range_rate = range_rate_from_velocity(
//!     Vec3::new(7_000_000.0, 0.0, 0.0),
//!     Vec3::new(1_000.0, 0.0, 0.0),
//! );
//! assert_eq!(range_rate, Some(1_000.0));
//!
//! let shift = DopplerShift::from_range_rate(12.0e9, 1_000.0).expect("valid");
//! assert!(shift.shifted_frequency() < 12.0e9);
//! ```

#![forbid(unsafe_code)]
#![deny(missing_docs)]

mod shift;

pub use shift::{
    DopplerShift, acquisition_span, angle_from_range_rate, classical_shift, maximum_shift,
    range_rate_from_velocity, relativistic_doppler_factor,
};

pub use apsis_core::constant::SPEED_OF_LIGHT;
pub use apsis_math::Vec3;