62 lines
2.7 KiB
Rust
62 lines
2.7 KiB
Rust
//! Inter-satellite link geometry and visibility.
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//!
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//! Two satellites can form a link when the straight line between them does
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//! not pass through the Earth. This crate decides that condition, gives the
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//! geometry a link budget needs, and reports the range and the angles at
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//! which each satellite must point.
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//!
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//! The blocking test is whether the line segment between the two positions
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//! has any point inside the body. For a spherical body that is a
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//! perpendicular distance test, which is exact and cheap, so it is the one
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//! used here.
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//!
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//! An optical link adds a second condition: the Sun must not be within the
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//! field of view of either terminal, because the background would swamp the
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//! signal. That is a separate test, offered as [`sun_blocks_link`], which
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//! takes the direction to the Sun.
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//!
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//! Lengths are in kilometers and angles in radians. The positions are in a
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//! frame in which the Earth is a sphere of the given radius, which for link
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//! geometry is the same frame the orbit layer produces.
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//!
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//! ```
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//! use apsis_isl::{LinkGeometry, link_geometry, mutual_visibility};
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//! use apsis_math::Vec3;
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//!
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//! // Two satellites on the same side of the Earth see each other.
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//! let first = Vec3::new(6_928.137, 0.0, 0.0);
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//! let second = Vec3::new(6_868.137, 2_500.0, 0.0);
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//! assert_eq!(mutual_visibility(first, second, 6_378.137), Some(true));
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//!
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//! // Two satellites on opposite sides do not.
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//! let opposite = Vec3::new(-6_928.137, 0.0, 0.0);
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//! assert_eq!(mutual_visibility(first, opposite, 6_378.137), Some(false));
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//! ```
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//!
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//! 星间链路几何与可见性。
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//!
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//! 当两颗卫星之间的直线不穿过地球时，它们可以形成一条链路。本 crate 判定该条件、
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//! 给出链路预算所需的几何，并报告距离以及每颗卫星必须指向的角度。
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//!
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//! 遮挡判据是两点之间的线段是否有点位于天体内部。对球形天体而言这是一个垂距判定，
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//! 它精确且廉价，故此处采用它。
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//!
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//! 光链路还加一个条件：太阳不得位于任一终端的视场内，因为背景会淹没信号。那是一个
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//! 单独的判定，作为 [`sun_blocks_link`] 提供，它接收太阳方向。
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//!
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//! 长度以千米计，角度以弧度计。各位置所在的坐标系中地球是给定半径的球，对链路
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//! 几何而言它与 orbit 层所产生的是同一坐标系。
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#![forbid(unsafe_code)]
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#![deny(missing_docs)]
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mod batch;
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mod geometry;
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mod link;
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pub use batch::{visibility_matrix, visibility_matrix_parallel};
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pub use geometry::{closest_approach_to_centre, link_geometry, mutual_visibility, sun_blocks_link};
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pub use link::{LinkGeometry, LinkState};
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pub use apsis_math::Vec3;
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