Thanks Jeff for the info. Do I understand correctly that you generate your own curve fit to the GRS data in Jmess.dat, and that gets you accuracy within a few degrees (longitude)? That's very promising. How do you read that file? What do the section heading and columns mean? I knew that Jmess.dat file was significant to how WinJUPOS stays up to date, but I wasn't sure how.
Funny story, I was wondering how WinJUPOS stays up to date, so I used Wireshark to watch TCP traffic while I opened up WinJUPOS, and I saw that it sends a get request for Jmess.dat. The remote site returns a bunch of binary. I just now found the Jmess.dat file in my WinJUPOS app data directory and I can see it's just an ASCII file in some sort of lookup table format. I couldn't find that file just searching google or trying various urls at the host address, but it looks like I might be able to get to it programmatically through an http request.
Anyways, since you're here and interested, please tell me, would a Jupiter renderer tool be useful to you? How would you use it? Are all three CMs useful? How would you suggest rendering the planet.. using a static texture map or maybe a simplified cartoon just showing the extents of the main bands and GRS, plus moons and shadows? Any other ideas?
EDIT: found the Jmess data table decoder in Grischa Hahn's dissertation:
Format: OBJEKT REGION ta te t0 l0 S Drift [ß"]
Bsp.: WC WOS-DE C3 19980101 19980707 19980301 111.3 2 -0.345 -32.1
Ahah! In my Jmess.dat file I see objects "rs" (as in Grs), "wos-fa", "wos-de", and "wos-bc" which JUPOS documentation tells me are long-lived white ovals.. the pearls that trail behind and south of the GRS! Cool!
Translating the subsequent description in GH's thesis:
The values ta, te and t0 are start, end and reference dates in the format YYYYMMDD and refer to 12 UT (Universal Time) of the specified day. l0 is the jovigraphic length position of the object at time t0 in the rotation system S. Drift denotes the daily change in length position in [° / day]. Optionally, the jovigraphic latitude "ß" can be specified in [°]
Hmm.. "start", "end", and "reference" dates? Presumably "length position" = longitude, and the rest looks easy enough.
last 2 entries in Jmess.dat:
?c rs e3 20181126 20191227 20190610 310.8 2 +0.0572 -22.5
?c rs e3 20191228 20210128 20200714 337.7 2 +0.0713 -22.5
Can I just grab that last entry, from July 14, at 337.7 deg longitude, and propagate that +0.0713 deg per day? That yields 345 deg. Indeed, WinJUPOS shows GRS centered at 345 deg in L2 system!
Am I doing this right?
Edited by rkinnett, 19 October 2020 - 09:03 PM.