GREOPy: A General Relativistic Emitter-Observer problem Python algorithm

[irideselby]

Submitting Author: Jan P. Hackstein (@irideselby)
All current maintainers: (@irideselby)
Package Name: GREOPy
One-Line Description of Package: Calculate relativistic light rays sent by an emitter to a receiver in the presence of a gravitational field.
Repository Link: https://codeberg.org/JPHackstein/GREOPy
Version submitted: v0.2.1
EiC: @coatless
Editor: TBD
Reviewer 1: TBD
Reviewer 2: TBD
Archive: https://zenodo.org/records/14537866
JOSS DOI: TBD
Version accepted: TBD
Date accepted (month/day/year): TBD

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Description

GREOPy is a Python library for calculating relativistic light rays sent by an emitter to a receiver in the presence of a gravitational field. Finding a light ray connecting two events is sometimes called "Emitter-Observer" problem and is always present when it comes to communication between two observers, e.g. two satellites in orbit. GREOPy allows the emitter and receiver to move along arbitrary curves, making this an initial-value problem to solve from the emitter's perspective, and the gravitational field can be described by a rotating, non-accelerating central mass. Everything is being calculated in the general relativistic framework to include relativistic effects like light bending and the relativistic Doppler effect to be able to quantify their impact on error propagation. While only two spacetimes are implemented at the moment (even though further additions are planned), GREOPy is written in a way to allow the community to easily expand the number of spacetimes to suit their needs.

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Data processing/munging: GREOPy uses parametrised curves, e.g. orbit data, to simulate communication via relativistic light rays between them. This allows analysis of relativistic effects on light and by extension any corresponding observable in some chosen spacetime, giving insights into fundamental properties of the underlying spacetime.

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This package is mainly targeted for scientists working in geodesy; it can be used to simulate satellite-satellite or satellite-ground station communication and from this derive, e.g. how the Earth mass distribution changes over time due to for example climate change.

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Not the same thing. There exist of course Python packages that implement General Relativity, e.g. to be able to calculate light rays (lightlike/nulllike geodesics) as one can do with EinsteinPy for example. However there appear to be no packages that implement specifically the Emitter-Observer problem (initial-value problem with a variable target boundary) in terms of General Relativity.

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[coatless]

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Editor comments

Thanks for bearing with us as we hibernated over the holidays and assigned out a new EiC.

Regarding the package, I'm happy to work on assigning an editor.

However, I do want to bring to your attention a few concerns.

Specifically, the "How to find initial conditions" page linked on the documentation website is blank.

https://greopy.readthedocs.io/en/latest/about/initial_conditions.html

Also, the tutorial gallery only one tutorial is present ("Quick Start"). Do you envision additional tutorials being added during the review process?

https://greopy.readthedocs.io/en/latest/auto_tutorials/index.html

Lastly, the Quickstart example on the reduced grid also took about 15 minutes of compute time on Colab. Would it be possible to include a note on the documentation that computations may be long running?

[irideselby]

Hello!
Thank you very much for your answer and comments.
Concerning the blank page on the wiki. It has sadly been sitting there for a while while I was working on different aspects of the package and it has been slipping through until now, but I think now will be a good time to finally update it.
I definitely want to fill the tutorial gallery with more tutorials over time, and I think I have a good idea about a second small tutorial already. Now that I got the package into shape I can also focus more on tutorials.
Also thank your for the notice on computation times, I will add a note to the documentation.

I will begin working on the comments in the next couple of days and update everything accordingly, so thanks again!
Maybe one question: Between submitting the package and now, I have found a bug concerning the light ray calculation for which I have worked out a fix. May I just update the package while the review process is going on? I imagine that the review process will be conducted with the exact version I submitted, so in case the bug will be found by the reviewers as well, do I then just link to the package version/PR that fixes the bug?

[coatless]

@irideselby Okay, let's hold off on sending it out for the review until the bug regarding light ray calculation is fixed as that may impact what SME reviewers of the software respond with.

Sound okay?

[irideselby]

@coatless Thank you for waiting, I fixed the bug and bumped the version accordingly. I also edited the initial message in this thread to reflect this change, so now the submitted version is 0.2.1 instead of 0.2.0, I hope that's alright.

[coatless]

@irideselby thanks for letting me know. I'll start the process of assigning an editor.

[irideselby]

I have now added the paper.md for JOSS in a paper/ directory and added a tick for the corresponding bullet point in the initial submission message.