Class Name: GEI Location 3D

Superclass - Location 3D

Definition

A coordinate within the Geocentric Equatorial Inertial (GEI) 3D Spatial Reference Frame (SRF).

The Geocentric Equatorial Inertial Spatial Reference Frame, also known as Earth Centered Inertial (ECI) or Geocentric Celestial Inertial (GCI), is based on a Cartesian coordinate system with 3 orthogonal axes and an origin at the mass-center of the Object Reference Model/Earth Reference Model (ORM/ERM) as defined by the World Geodetic System (WGS) 1984 ellipsoid. The X axis is defined as pointing in the direction of the first point in Aries (vernal equinox) in the Rotational Equatorial and Ecliptic planes. The Z axis is defined as the polar axis (coincident with the ORM/ERM rotational axis) and pointing north. The Y axis is defined as orthogonal to the other two axes and in the ORM/ERM equatorial plane, so as to form a right-handed orthogonal set.

Locations are defined as {ra, dec, r} triplets from the origin (ORM/ERM mass-center). Right Ascension (ra) is defined as the geocentric angle between the projection of the radius vector onto the rotational equatorial plane and the vernal equinox; it is positive towards the east. Declination (dec) is defined as the geocentric angle between the radius vector and the Equatorial plane; it is positive towards the north. R is the magnitude of the radius vector in meters.

See the SEDRIS Spatial Reference Model (SRM) for additional details.

Primary Page in DRM Diagram:

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Example

GEI provides a convenient system for

1. Defining the positions of orbital satellites.
2. Describing space vehicle dynamics.
3. Providing astronomical data.

FAQs

Is GEI an inertial coordinate system?

GEI is independent of the Earth's surface, and the Earth's position with respect to the Sun -- it is fully inertial.

Constraints

• Environment Root Spatial Reference Frame
• Locations Under Model

Component of (one-way)(inherited)

• optionally, some Arcs
• optionally, some Base Perimeter Data
• optionally, some Base Reference Vectors
• optionally, some Directional Light Behaviors
• optionally, a Distance Level of Detail Data (notes)
• optionally, some Ellipses
• optionally, some Elliptic Cylinders
• optionally, some Feature Edges
• optionally, a Feature Node
• optionally, some Image Anchors
• optionally, some Labels
• optionally, a Location Table
• optionally, some Morph Points
• optionally, some Point Geometries
• optionally, some Property Grid Hook Points
• optionally, a Reference Origin
• optionally, some Spatial Domains
• optionally, some Spatial Index Related Feature Topologies
• optionally, some Spatial Index Related Features
• optionally, some Spatial Index Related Geometries
• optionally, some Tack Points
• optionally, some Vertices
• optionally, some Vertex with Component Indices
• optionally, some World 3X3s
• optionally, some World Transformations
• optionally, an Attachment Point
• optionally, some Center of Buoyancies
• optionally, some Center of Mass
• optionally, some Center of Pressures
• optionally, a Contact Point
• optionally, some Positional Lights
• optionally, some Separating Planes
• optionally, some Sound Instances
• optionally, some Stamp Behaviors
• optionally, some Volumes
• optionally, some Volume Level of Detail Data
• optionally, some Volume Light Behaviors

Field Elements

Notes

Component of Notes

Distance_Level_of_Detail_Data

 the center point for the LOD test

Fields Notes

right_ascension

 in degrees of arc

declination

 in degrees of arc

radius

 distance from the mass-center of the reference object;
 non-negative; in meters