Suggested improvements

[ljbade]

The locationcart() functions for Sun, planets and the Moon don't document their reference frame (e.g. equatorial vs ecliptic). So far I have worked out the planets return equatorial plane Cartesian coords.

In addition they all need to clearly state the origin of the coordinate system (e.g. heliocentric, geocentric or barycentric). So far I have worked out the SUN positions are geocentric, but the planets are heliocentric.

The Date struct is not very clear what julian() is, it should explicitly state it's the Julian Date in units of days.

The Coord struct could also do with some improvements, for example it isn't easy to get Cartesian coordinates in the ecliptic plane which I wanted in my project. It could also do with some functions to convert au coords to metres or kilometres,

[ljbade]

I can't figure out what coordinates are being returned for the moon. They don't seem to line up with the values from NASA JPL Horizons no matter the combination of equatorial, ecliptic, or the current Earth orientation, and combinations of heliocentric or geocentric. Certainly looks like the moon module's XYZ axis are not in the same direction as the XYZ axis for the Earth coordinates calculated in the sol module.

[iriswebb]

Commit 05ddb5f

The locationcart() functions for Sun, planets and the Moon don't document their reference frame (e.g. equatorial vs ecliptic). So far I have worked out the planets return equatorial plane Cartesian coords.

In addition they all need to clearly state the origin of the coordinate system (e.g. heliocentric, geocentric or barycentric). So far I have worked out the SUN positions are geocentric, but the planets are heliocentric.

There is "relative to the Sun/Earth" in the documentation, but I'll specify explicitly whether it's geocentic or heliocentric

The Date struct is not very clear what julian() is, it should explicitly state it's the Julian Date in units of days.

There is documentation at the start of the file that specifically mentions that it's the Julian Date, but I forgot to specify that in the function documentation

The Coord struct could also do with some improvements, for example it isn't easy to get Cartesian coordinates in the ecliptic plane which I wanted in my project.

You can hack them in:

let (lambda, beta) = original_coordinate.ecliptic(observation_time);
coord::Coord::from_equatorial(lambda, beta).cartesian()

It could also do with some functions to convert au coords to metres or kilometres,

https://github.com/oliverkwebb/deskephem/blob/main/src/value.rs#L108

I can't figure out what coordinates are being returned for the moon. They don't seem to line up with the values from NASA JPL Horizons no matter the combination of equatorial, ecliptic, or the current Earth orientation, and combinations of heliocentric or geocentric. Certainly looks like the moon module's XYZ axis are not in the same direction as the XYZ axis for the Earth coordinates calculated in the sol module.

They are geocentric and in AU, I believe

[ljbade]

Thanks for the responses.

You could put those au to other unit conversion constants in a pub const which would save user needing to add them themselves.

I will try out that code for the ecliptic coords.

I used Claude Code to have a look at what is going on with the Moon coordinates, this is what it found:

// Moon: pracstro computes geocentric ecliptic (λ,β) internally, but locationcart()
// uses a buggy Coord::cartesian() that treats RA as a polar angle instead of azimuthal.

After implementing its suggested fix the moon now appears in the right location.

[iriswebb]

// Moon: pracstro computes geocentric ecliptic (λ,β) internally, but locationcart()
// uses a buggy Coord::cartesian() that treats RA as a polar angle instead of azimuthal.

Commit 0196b4b (pracstro 1.1.1)

Thanks for pointing that out