Coordinate systems

This folder implements the coordinate systems used in geodesy, following the classical classification below:

Fig. 1: Relationship between geocentric, topocentric, and 2D coordinate systems

• Geocentric systems (origin at the Earth's center):
  • IT — Instantaneous Terrestrial: tied to the true (instantaneous) rotation axis; related to CT through polar motion (x_P, y_P)
  • CT — Conventional (Average) Terrestrial: the Earth-fixed frame the others are referred to
  • G — Geodetic: latitude φ, longitude λ, height h on a reference ellipsoid; related to CT by the datum parameters (x₀, y₀, z₀, ε_X, ε_Y, ε_Z)
• Topocentric systems (origin at an observer on the surface):
  • LA — Local Astronomic: aligned with the plumb line (astronomical Φ, Λ)
  • LG — Local Geodetic: aligned with the ellipsoid normal (φ, λ); LA ↔ LG differ by the deflection of the vertical (ξ, η) and azimuth correction ΔA
• Celestial / orbital systems: AP — Apparent Places (related to IT through GAST), OR — Orbital
• Mappings take geodetic coordinates to 2D coordinate systems — implemented in MapProjections

Systems in this folder

Each subfolder follows the same four-file pattern: the coordinate-system class, a strongly-typed …Point class, and their two interfaces. Points are generic over measurement units (e.g. Meter/Degree) from IRI.Maptor.Core.Common.Metrics.

Folder	Coordinates	Used for
Cartesian2D	X, Y (LinearUnit)	Planar/projected coordinates
Cartesian3D	X, Y, Z (LinearUnit)	Geocentric frames (CT, IT) and datum shifts
Polar	Radius, Angle	2D polar coordinates
Curvilinear.Spherical	Radius, HorizontalAngle, VerticalAngle	Spherical approximations, astronomy
Curvilinear.Ellipsoidal	HorizontalAngle, VerticalAngle + Datum	Angular coordinates on a reference ellipsoid
Curvilinear.Ellipsoidal/Curvilinear.Astronomical	HorizontalAngle, VerticalAngle	Astronomical (plumb-line) coordinates — LA, AP, HA
Curvilinear.Geodetic	Latitude, Longitude, Height + Datum	The geodetic system (G) — lat/lon/height on an ellipsoid

Basic usage

GeodeticPoint<TLinear, TAngular> is the workhorse: a φ/λ/h position bound to a datum (Ellipsoids), convertible to geocentric Cartesian:

using IRI.Maptor.Core.Common.Metrics;
using IRI.Maptor.Core.SpatialReferenceSystem;

var point = new GeodeticPoint<Meter, Degree>(
    Ellipsoids.WGS84,
    new Meter(0),                // ellipsoidal height
    new Degree(51.123456),       // longitude
    new Degree(35.123456));      // latitude

var cartesian = point.ToCartesian<Meter>();   // geocentric X, Y, Z

Converting between systems

The static Transformations class implements the arrows of Fig. 1:

Conversion	Methods
CT ↔ IT	AverageToInstantaneous / InstantaneousToAverage
CT ↔ G	AverageToGeodetic / GeodeticToAverage
G1 ↔ G2 (datum change)	ChangeDatum
CT ↔ LA	AverageToLocalAstronomic / LocalAstronomicToAverage
G ↔ LG	GeodeticToLocalGeodetic / LocalGeodeticToGeodetic
LA ↔ LG	LocalAstronomicToLocalGeodetic / LocalGeodeticToLocalAstronomic
LA ↔ HA	LocalAstronomicToHorizontalAngle / HorizontalAngleToLocalAstronomic
HA ↔ AP	HorizontalAngleToApparentPlace / ApparentPlaceToHorizontalAngle
IT ↔ AP	InstantaneousToApparentPlace / ApparentPlaceToInstantaneous
OR ↔ AP	OrbitalToApparentPlace / ApparentPlaceToOrbital

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