Coordinate Systems and Transforms in Space Physics: Terms, Definitions, Implementations, and Recommendations for Reproducibility

TL;DR

This paper highlights the inconsistencies in coordinate system definitions in space physics, emphasizing the need for standardized references, a central database, and transparent software implementations to improve reproducibility.

Contribution

It compares existing definitions and implementations of coordinate systems, proposing standards, a reference database, and best practices for reproducibility in space physics research.

Findings

Implementation differences can cause significant discrepancies in transformations.

Current definitions and data sources lack standardization, hindering reproducibility.

Recommendations for establishing standards and documentation practices are provided.

Abstract

In space physics, acronyms for coordinate systems (e.g., \texttt{GEI}, \texttt{GSM}) are commonly used; however, differences in their definitions and implementations can prevent reproducibility. In this work, we compare definitions in online resources, software packages, and frequently cited journal articles and show that implementation differences can lead to transformations between same-named coordinate systems and position values from different data providers to differ significantly. Based on these comparisons and results, and to enable reproducibility, we recommend that (a) a standard for acronyms and definitions for coordinate systems is developed; (b) a standards body develops a citable database of reference data needed for these transforms; (c) a central authority maintains the SPICE (Spacecraft, Planet, Instrument, C-matrix, Events) kernels used by space physics spacecraft missions to generate data products in different coordinate systems; and (d) software developers provide explicit comparisons of their implementations with the results of (b) and documentation on implementation choices. Additionally, we provide recommendations for scientists and metadata developers to ensure that sufficient information is provided to enable reproducibility.