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This presentation outlines revisions to the Object Reference Model (ORM) to enhance its capabilities, including new specifications, definitions, and generalizations. It addresses dependency of coordinate systems on Object Reference Surfaces (ORS) and proposes a Celestial Body Reference Model (CBRM). The goal is to make the ORM applicable to celestial bodies beyond Earth.
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Proposed Revisions to the ORM Presentation given to WG8 Meeting #5 Orlando by Paul A. Birkel November 28 - December 1, 2000
Overview of Proposed Revisions • Refine Object Reference Model to allow0 or more Object Reference Surfaces (ORS) • Define ORS and characterize those which will appear in this International Standard • Characterize dependency of “categories” of CS on ORS (e.g., projection-based CS on sphere or ellipsoid of revolution) • Generalize from “geo” (and Earth) to “celestio”, as appropriate (e.g., ORM, CRM, ERM) • Reorganize/rename “categories” of SRFs and incorporate choices of ORM, ORS(s), and CS
Object Reference Model • Current: An Object Reference Model is an n-dimensional surface. • New: An Object Reference Model is a specification of at least N-1 (where N is the dimensionality of the object) distinguished orthogonal directions, and a distinguished point. It may optionally include the specification of one or more associated Object Reference Surfaces. The distinguished point and the distinguished orthogonal directions may together be used to form an object-centric coordinate system.
Example ORM: Planetary Object • N-1 = 2 distinguished orthogonal directions -- derived from an axis, and some plane containing a second axis. • The axis may relate to rotation, magnetics, or be fixed to an external frame. • The plane may be rotational, perpendicular to a magnetic axis, or ecliptic (among other choices). • The axis-in-the-plane may be defined by a unique point on an associated ORS (e.g., a crater), an equinox, or some external point. • The distinguished point may be a mass-center. • The associated Object Reference Surface(s) may be: • Absent, • Based on a sphere, an ellipsoid of revolution, a tri-axial ellipsoid, a surface of constant gravitational potential, a “well-known” surface such as “mean sea level”, a surface of constant pressure, or • Some combination of these alternatives (e.g., an ellipsoid of revolution, and a surface of constant gravitational potential).
Significant ORS (currently) Define and incorporate additional ORS’s as required.
Generalization of ORM/ERM • This International Standard should (also) apply to non-Earth objects, including: • Sun, planet, natural satellite, asteroid, and space-based man-made objects. • As currently drafted, it provides for only the most general case (which covers LSR/LSR2) and the Earth-specific case of ORMs (a specific planet). • An intermediate case is required, perhaps termed the Celestial Body Reference Model (CBRM) • where “celestial body” is scoped to include suns, planets, natural satellites, and asteroids -- of which the ERM is a special case.
Removing Earth-centrism • The following existing terms should be revised, wherever they appear in this International Standard excepting where the intended scope is exactly the Earth: * *As in “geographic”, “planetographic” (and “cartographic”)
