Scripting API Question - Adding Custom Object J2000 vs Ra/Dec

[sgano]

Hello, I am working on a script to add a custom object and have some questions about the API. Specifically related to:
CustomObjectMgr.addCustomObject(QString designation, Vec3d coordinates, bool isVisible=false)

I have added the object with lines like this:
var positionXYZ = core.vec3d(objX,objY,objZ); // Example vector
CustomObjectMgr.addCustomObject("J2000", positionXYZ, true);

Where each of the objX, objY, and objZ are J2000 Cartesian coordinates in AU (units).

My questions are:
(1) Is this Vec3D supposed to be in AU units?
(2) does it have to be a unit vector?
(3) Assuming it is not a unit vector - I was trying to add this object with J2000 coordinates for an Earth Orbiting object (in Low Earth Orbit). Presumably if I add J2000 coordinates, then this object should be placed properly for different locations on Earth and since it is in LEO the Ra/Dec will change due to Parallax depending on where you are located. -- Or is this not how this works?

I ask this because, I have computed the RA and Dec for this object (using a Python library) and
using these values with this function in the script:

CustomObjectMgr.addCustomObject(QString designation, const QString &ra, const QString &dec, bool isVisible=false)

where I enter the Ra/Dec directly yields a different location in the sky than the J2000 coordinates version of this function and I am trying to understand why they are different.

Thank you!

[gzotti]

In my understanding these custom objects are to be understood on the celestial sphere, so unit vector. LEO objects are calculated in the Satellites plugin with TLE elements, and moving solar system objects are described via Kepler elements. Maybe you can extend the Satellites plugin with script-based injection of arbitrary custom objects that do not move on orbits that can be described in TLE. Else when you add objects in a unit-vector J2000 position they should be in the sky at those J2000 coordinates regardless of where are located on Earth.

[sgano]

That helps a lot, thank you! That confirms my suspicion that the Vec3d was treated like a unit vector and I don't need to further investigate why they are different. Modifying the satellite plugin is probably the right way, or just doing all of the coordinate conversions from J2000 coordinates in the script itself based upon the current location and time. For now I will stick with converting them in Python for each location on Earth over a large time period that I write to a file which I can read into the .ssc script (which uses a lookup table based on the time and when the time is changed in Stellarium it updates the custom object location [Ra/Dec]. I will share back what I come up with to this forum (as someone else may find it useful in the future).