ISO 19161-1:2020

Overview

ISO 19161-1:2020 - Geographic information - Geodetic references - Part 1: International terrestrial reference system (ITRS) defines the basic information and requirements for the International Terrestrial Reference System (ITRS), its realizations and how to access and use them. The standard aligns terminology and definitions with the International Union of Geodesy and Geophysics (IUGG), the International Association of Geodesy (IAG) and the International Astronomical Union (IAU). It describes primary and secondary realizations (including the International Terrestrial Reference Frame, ITRF), categorizes realization procedures, and provides normative guidance on position determination.

Key topics and requirements

• Definitions and scope: Clarifies ITRS as the geocentric terrestrial reference system used for precise positioning and reference frame maintenance.
• Primary vs. secondary realizations:
  • Primary realizations are the ITRF products produced by the International Earth Rotation and Reference Systems Service (IERS) (ISO does not redefine or set requirements for ITRF production).
  • Secondary realizations are terrestrial reference frames aligned to an ITRF and may be called implementations or densifications.
• Alignment and transformation: Secondary realizations must be aligned to a primary/secondary ITRS using 7-parameter (positions) or 14-parameter (positions + velocities) similarity transformations to ensure consistent origin, scale, orientation and time evolution.
• Types of terrestrial reference frames (TRF):
  • Crust-based TRF (geodetic markers, tracking instruments; global, regional or local networks).
  • Satellite-ephemerides-based TRF (numerical trajectories of satellite centers of mass expressed in ITRS).
• Representation formats: Coordinates at specified epochs, time series, or parameterized functions of time (static, kinematic or dynamic realizations).
• Normative methods and access: Annex A provides methods for determining positions in an ITRS realization and access mechanisms; Annex B and C give informative descriptions and lists of major aligned frames.
• Conformance: Secondary realizations must demonstrate alignment and consistency with an ITRF-compliant realization to claim conformance.

Applications and users

ISO 19161-1:2020 is relevant to:

• Geodesists and national mapping agencies maintaining national TRFs or densifications.
• GNSS service providers and satellite navigation teams requiring ITRF-aligned frames.
• Surveyors, GIS professionals and infrastructure monitoring teams needing consistent positioning references.
• Space agencies, oceanography and earthquake monitoring programs that depend on precise global reference systems.

Keywords: ISO 19161-1:2020, ITRS, ITRF, terrestrial reference frame, geodetic references, GNSS, satellite ephemerides, IERS, geodesy.

Related standards and references

• ISO 19111:2019 (coordinate referencing)
• IERS Conventions and ITRF products (primary realization authority)
• Annex C of ISO 19161-1 summarizes major reference frames aligned to ITRF (e.g., GNSS-specific frames).