Hi. This might seem a bit of a strange question. Or questions. Or rather line of questioning. But it all focuses on how Stellarium works with respect to the Great Red Spot positioning on Jupiter.
Can a developer confirm, please, that the rot_rotation_offset value has nothing to do with the "real" Jupiter GRS longitude that one might obtain from JUPOS? For example, the GRS longitude is approximately 192 today (7 Apr 2013). My assumption is that the Stellarium offset simply rotates the Jupiter texture image, like one might rotation a landscape image to correspond to north.
Can someone recommend a "good" value for the rot_rotation_offset setting, assuming one is using the latest version of Stellarium, say 0.12.0 or 0.12.1? I believe I discovered the value of 315 in the ssystem.ini file of a recent install. I adjusted it to 310 which seems a little better. Of course, the GRS moves about 10 degrees a year (Earth year that is).
Is it my imagination or do these numbers NOT apply across versions? I have found that I need to use 140 in version 0.9.x and 80 in version 0.11.x. Why are the numbers different? I assume it is because the Jupiter texture is different. Certainly there's a difference between 9 and 11, the images are unique. And a comment inside the version 12 ini suggests there's a new image for that version. If this can be confirmed, then it will help in supporting the product. Version specific numbers can be recommended.
Finally, does anyone know why there might be a discrepancy among users of the same version. I'm using 315 on version 12 under Windows 7 while a colleague (in the same general geographical area) is using 140 on version 12 under Windows Vista. Why wouldn't we use the exact same numbers? We both of light speed on. Could this be attributed to inconsistencies in date, time, time zone, etc. between our two computers?
Sorry for the long message. But I've spent a good part of the day trying to decipher why Stellarium is acting the way that it is. As I often recommend and assist people with Stellarium, I'd like to be able to give correct instructions and advice.
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Yes, the rot_rotation_offset value has nothing to do with the "real" Jupiter GRS longitude because Stellarium use "inner" longitude for planets.
A "good" values for longitude of GRS can be get from direct observations of Jupiter. Since 0.11.4 Stellarium used the simple equation for calculation of the shift of GRS. This is not ideal but better that before - static position of Jovian GRS.
Yes, this is related to texture of Jupiter + technically this file contains "actual" value for GRS on release dates (for fresh install of course).
This is very weird - this shouldn't be of course. Can you give some technical info about that installations?
Technically we have plan for improvement of calculation of the GRS (https://blueprints.launchpad.net/stellarium/+spec/great-red-spot) but right now I'm suspended it for version 0.12.2. I think I can set for Jovian rot_rotation_offset the real longitude and just use additional shift for calculation of "inner" longitude.
P.S. Don't worry, your message is good.