deep_time/
position.rs

1use crate::{C_SQUARED, Real, hypot, sqrt};
2
3/// A 3-dimensional position vector expressed in Cartesian coordinates (x, y, z)
4/// with units of meters (SI).
5///
6/// This type is designed for high-precision relativistic calculations in space
7/// navigation, deep-space tracking, and interplanetary timing. Positions are
8/// typically expressed in a heliocentric (Sun-centered) reference frame because
9/// the dominant gravitational light-time correction—the Shapiro delay—is
10/// calculated with respect to the Sun.
11#[derive(Clone, Copy, Debug, PartialEq)]
12#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
13#[cfg_attr(feature = "js", derive(tsify::Tsify))]
14pub struct Position {
15    pub x: Real,
16    pub y: Real,
17    pub z: Real,
18}
19
20impl Position {
21    /// Creates a new `Position` directly from its Cartesian components in meters.
22    #[inline]
23    pub const fn new(x: Real, y: Real, z: Real) -> Self {
24        Self { x, y, z }
25    }
26
27    /// The zero vector, representing the origin of the coordinate system
28    /// (commonly the center of the Sun).
29    pub const ZERO: Self = Self::new(f!(0.0), f!(0.0), f!(0.0));
30
31    /// Creates a `Position` from coordinates expressed in Astronomical Units (AU),
32    /// converting them to meters using the exact IAU 2012 definition
33    /// (1 AU = 149 597 870 700 m).
34    ///
35    /// Especially convenient when working with planetary ephemerides or solar-system
36    /// models that are natively given in AU.
37    #[inline]
38    pub const fn from_au(x: Real, y: Real, z: Real) -> Self {
39        const AU: Real = f!(1.495978707e11);
40        Self {
41            x: x * AU,
42            y: y * AU,
43            z: z * AU,
44        }
45    }
46
47    /// Returns the Euclidean norm (straight-line distance) of this position from
48    /// the origin.
49    ///
50    /// When the position is Sun-centered, this is the radial distance from the Sun
51    /// required for Shapiro-delay calculations.
52    #[inline]
53    pub const fn norm(self) -> Real {
54        hypot(hypot(self.x, self.y), self.z)
55    }
56
57    /// Computes the straight-line (Euclidean) distance between this position and
58    /// another `Position`.
59    ///
60    /// Together with the two radial distances from the Sun, this value supplies the
61    /// three geometric inputs needed to evaluate the Shapiro delay.
62    pub const fn distance_to(self, other: Self) -> Real {
63        let dx = self.x - other.x;
64        let dy = self.y - other.y;
65        let dz = self.z - other.z;
66        hypot(hypot(dx, dy), dz)
67    }
68
69    /// Returns a new position that lies a fraction `t` of the way along the straight
70    /// line between `self` and `other`.
71    ///
72    /// This is known as linear interpolation (lerp). It is most commonly used when
73    /// you need to generate evenly spaced sample points along a path — for example,
74    /// when building the `samples` slice for [`ObserverState::one_way_relativistic_delay_integrated`].
75    ///
76    /// # Parameters
77    /// - `other` – the ending position
78    /// - `t` – interpolation parameter (0.0 = start point, 1.0 = end point).
79    ///   Values outside [0, 1] are allowed and will extrapolate.
80    ///
81    /// # Examples
82    ///
83    /// ```rust
84    /// use deep_time::Position;
85    ///
86    /// let a = Position::new(0.0, 0.0, 0.0);
87    /// let b = Position::new(10.0, 20.0, 30.0);
88    ///
89    /// let midpoint = a.lerp(b, 0.5);           // (5.0, 10.0, 15.0)
90    /// let quarter   = a.lerp(b, 0.25);         // (2.5, 5.0, 7.5)
91    /// let beyond    = a.lerp(b, 1.5);          // (15.0, 30.0, 45.0)
92    /// ```
93    #[inline]
94    pub const fn lerp(self, other: Self, t: Real) -> Self {
95        Self::new(
96            self.x * (f!(1.0) - t) + other.x * t,
97            self.y * (f!(1.0) - t) + other.y * t,
98            self.z * (f!(1.0) - t) + other.z * t,
99        )
100    }
101}
102
103/// A 3-dimensional velocity vector expressed in Cartesian coordinates (vx, vy, vz)
104/// with units of meters per second (SI).
105#[derive(Clone, Copy, Debug, PartialEq)]
106#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
107#[cfg_attr(feature = "js", derive(tsify::Tsify))]
108pub struct Velocity {
109    pub vx: Real,
110    pub vy: Real,
111    pub vz: Real,
112}
113
114impl Velocity {
115    /// Creates a new `Velocity` directly from its Cartesian components in m/s.
116    #[inline]
117    pub const fn new(vx: Real, vy: Real, vz: Real) -> Self {
118        Self { vx, vy, vz }
119    }
120
121    pub const ZERO: Self = Self::new(f!(0.0), f!(0.0), f!(0.0));
122
123    /// Creates a `Velocity` from its scalar speed (magnitude) in m/s.
124    ///
125    /// Direction is set along the x-axis because only the speed matters
126    /// for relativistic calculations (`beta()`, `norm_squared()`, etc.).
127    /// This is the convenience constructor used by `Drift::from_velocity_potential_and_scale`.
128    #[inline]
129    pub const fn from_speed(speed_m_s: Real) -> Self {
130        Self::new(speed_m_s, f!(0.0), f!(0.0))
131    }
132
133    /// Returns the squared Euclidean norm (v²).
134    #[inline]
135    pub const fn norm_squared(self) -> Real {
136        self.vx * self.vx + self.vy * self.vy + self.vz * self.vz
137    }
138
139    /// Speed in m/s (Euclidean magnitude).
140    #[inline]
141    pub const fn speed(self) -> Real {
142        sqrt(self.norm_squared().max(f!(0.0)))
143    }
144
145    /// Dimensionless 3-velocity β = v/c relative to the local chrono-rest frame.
146    /// This is exactly what the master Lagrangian and `Spacetime` expect.
147    #[inline]
148    pub const fn beta(self) -> Real {
149        sqrt((self.norm_squared() / C_SQUARED).max(f!(0.0)))
150    }
151}
deep_time/position.rs

deep_time/
position.rs
