Crate icao_wgs84 

icao-wgs84

A library for performing geometric calculations on the WGS-84 ellipsoid, see Figure 1.

Figure 1 The WGS-84 Ellipsoid (not to scale) Cmglee, CC BY-SA 4.0, via Wikimedia Commons

WGS-84 has become the de facto standard for satellite navigation since its adoption by the Navstar Global Positioning System (GPS) and the USA making GPS available for civilian use in 1983.

This library uses the WGS-84 primary parameters defined in Tab. 3-1 of the ICAO WGS-84 Implementation Manual.

Geodesic navigation

The shortest path between two points on the surface of an ellipsoid is a geodesic segment. It is the equivalent of a straight line segment in planar geometry or a great circle arc on the surface of a sphere, see Figure 2.

Figure 2 A geodesic segment (orange) and a great circle arc (blue)

This library uses the correspondence between geodesic segments on an ellipsoid and great-circle arcs on a unit sphere, together with 3D vectors to calculate:

• the length and azimuths of a geodesic segment between two positions;
• the along track and across track distances of a point relative to a geodesic segment;
• and the intersection of two geodesic segments.

See: geodesic algorithms.

Design

The library is based on Charles Karney’s GeographicLib library.

Like GeographicLib, it models geodesic segments as great circle arcs on the surface of a unit sphere. However, it also uses vectors to perform calculations between geodesic segments.

The Ellipsoid class represents an ellipsoid of revolution. The static WGS84_ELLIPSOID represents the WGS-84 Ellipsoid which is used by the GeodesicSegment From traits to create GeodesicSegments on the WGS-84 Ellipsoid.

The library depends upon the following crates:

• angle-sc - to define Angle, Degrees and Radians and perform trigonometric calculations;
• unit-sphere - to define LatLong and perform great-circle and vector calculations.
• icao_units - to define Metres and NauticalMiles and perform conversions between them.

Figure 3 Class Diagram

The library is declared no_std so it can be used in embedded applications.

Modules

ellipsoid

The ellipsoid module contains types and functions for defining an ellipsoid given its Semimajor axis (the equivalent of its radius) and flattening ratio.

geodesic

The geodesic module contains functions for calculating the geodesic segment between two points on the surface of an ellipsoid.

intersection

The intersection module contains functions for calculating geodesic intersections using vectors.

Structs

Angle

An angle represented by it’s sine and cosine as UnitNegRanges.

Degrees

The Degrees newtype an f64.

Ellipsoid

The parameters of an Ellipsoid.

GeodesicSegment

A geodesic segment on the surface of an ellipsoid.

LatLong

A position as a latitude and longitude pair of Degrees.

Metres

A Metres newtype for representing distance.

NauticalMiles

A Nautical Mile newtype for representing distance.

Radians

The Radians newtype an f64.

Statics

WGS84_ELLIPSOID

A static instance of the WGS-84 Ellipsoid.

Traits

Validate

The Validate trait.

Functions

calculate_azimuths_and_geodesic_length

Calculate the azimuths and geodesic length (in metres) between a pair of positions on the ellipsoid.

calculate_intersection_distances

Calculate the distances along a pair of GeodesicSegments (in Radians) to their closest intersection or reference points.

calculate_intersection_point

Calculate the position (Latitude and Longitude) where a pair of GeodesicSegments intersect, or None if the GeodesicSegments do not intersect.