[PROJ] Non-Earth Based Coordinate Transforms

[Jérôme St-Louis]

Dear Daniel,

I worked with Martin in those OGC Testbed initiatives.

You may also be interested in OGC 22-035 which documented the use of the 
NOVAS library <https://aa.usno.navy.mil/software/novas_info> to perform 
conversions between Earth-Centered Earth-Fixed (ECEF) and Barycentric 
Celestial Reference System (BCRS):

https://docs.ogc.org/per/22-035.html#_cb4841e3-08d7-4a39-bb3f-132f334cbb3c 
(Section 6)

There's also a brief update on usage of NOVAS the BCRS in section 5 of 
OGC 23-042:

https://docs.ogc.org/per/23-042.html#_64ee1661-c316-47f7-9f5b-a0eff8dd170d 
(Section 5)

Here's a link to our related demo video for Testbed 19:

https://youtu.be/9ksHTB7S6zQ?t=2983

Kind regards,

-Jerome

On 1/29/25 3:43 PM, Martin Desruisseaux via PROJ wrote:
>
> Hello Daniel
>
> Le 2025-01-29 à 20 h 13, Daniel Garcia-Briseno via PROJ a écrit :
>
>> I'm a software developer on a NASA contract, I'm working on a web 
>> based platform that pulls data from various providers in different 
>> coordinate systems, but not all my coordinates are earth based. I 
>> recently discovered proj4js which led me to you.
>> Throughout your documentation there's a lot of "geo", but my data is 
>> a mix of "geo" and "helio" where my coordinates are relative to the 
>> sun, not the earth. Is there a way I could use proj to transform 
>> between earth-relative and sun-relative coordinates? I need to 
>> convert between a geocentric system and heliocentric system.
>
> The Open Geospatial Consortium (OGC) has conducted TestBeds in 2022 
> and 2023 on exactly those topics. OGC has published the following 
> engineering reports:
>
>   * 3D+ Data Space Object Engineering Report (23-011r1) —
>     https://docs.ogc.org/per/23-011r1.pdf
>   * Reference Frame Transformation Engineering Report (22-038r2) —
>     https://docs.ogc.org/per/22-038r2.pdf
>   * Non-Terrestrial Geospatial Engineering Report (23-042) —
>     https://docs.ogc.org/per/23-042.pdf
>   * Extraterrestrial GeoTIFF Engineering Report (23-028) —
>     https://docs.ogc.org/per/23-028.pdf
>
> A more complete list of Testbed engineering reports is at 
> https://www.ogc.org/completed-cosi-initiatives/
>
> Those engineering reports review some theoretical concepts about 
> referencing in space and mention some existing software such as NASA 
> SPICE. Then, they review how the OGC Topic 2 / ISO 19111 standard 
> (https://docs.ogc.org/as/18-005r8/18-005r8.pdf) can be used for the 
> definition of CRS in space. Those reports identify the following 
> classes which would need to be added to the existing international 
> standards:
>
>   * InertialCRS (you will need this one for referencing relative to
>     the Sun)
>   * MinkowskyCS (for Einstein's relativity)
>   * A few others
>
> Above-cited classes are not yet approved standards. However, they are 
> on the agenda for discussion in the ISO 19111 working group. It may 
> take a few years before they appear in standards, if accepted. A 
> proposal for encoding images in space in the GeoTIFF format has also 
> been submitted, but I think that the OGC GeoTIFF working group will 
> want to take a different approach than the one proposed in the last 
> engineering report.
>
> A prototype exists for the CRS in space and the GeoTIFF extension. As 
> a proof of concept, the TestBed implemented a scenario with the NASA 
> DART mission, where a satellite intentionally collided with an 
> asteroid for measuring the trajectory change. A chain of coordinate 
> operation from Earth to the satellite's moon has been implemented 
> using ISO 19111 + above-cited extensions. More details in above 
> engineering reports.
>
> Please do not hesitate to contact me if you have any question.
>
>     Regards,
>
>         Martin
>
>
>
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