A Question for Mr. Hutchison

[Bob Hegwood]

Grant,

I've had real problems using the Jupmoons.ssc which I originally downloaded from you. All of the locations appear to be correct except for *anything* on Amalthea. (In other words, all of the Callisto, Europa, and Io coordinates are correct, but the Amalthea coordinates are NOT.) Am I using the wrong texture for this moon? (In other words, has the standard Celestia Amalthea texture been set up with the Central Meridian located in the center of the image?)

Just thought I'd ask. There are only four Amalthea locations in that file, and *none* of them seem to line up correctly. There are two Facula defined in the location file, and the coordinates simply do *not* align themselves to two bright spots on Amalthea. The Pan crater is also not aligned to anything that I can see when Amalthea is displayed. Gaea DOES appear to line up with the huge dent in the middle of the 3ds model, but that's the only thing that does seem to align. I don't even know if THAT location is correct now though.

Any insight? Advice?

Thanks, Bob

[granthutchison]

Bob:
The Amalthea model and texture are correctly orientated. Pan is the huge dent in the northern hemisphere of Amalthea, just on the Jupiter side of the north pole. Gaea is the big south polar crater. Ida facula is a greenish-yellow smear straddling 180 degrees longitude in the northern hemisphere (on the side facing away from Jupiter), and Lyctos facula is another greenish area on the rim of a large unnamed crater on the leading hemisphere - it's at the centre of something of a webwork of greenish markings on high ground, so it doesn't stand out very well.
Unfortunately Celestia can't simulate a very wide range of albedo contrast, so the faculae aren't as prominent as they are in photos of Amalthea (which may well have had their contrast stretched, too), but they're definitely there and labelled appropriately.
Are you not seeing this?

Grant

[Bob Hegwood]

Mr. Hutchison,

I see the features you're describing, but they don't line up with the location labels...

I have used the default texture which came with 1.3.1, I've used a couple of other textures too - with the same result.

I finally found and installed Rassilon's excellent texture and model, (available at http://63.224.48.65/~rassilon/), but these too don't line up as they should.

I just thought I'd ask to see if there is something *else* I don't know about in this Central Meridian, latitude/longitude confusion.

Thanks very much for the information. I'll look at it some more.

Take care, Bob

[granthutchison]

Bob:
This is odd. Can we check if it's a problem with all 3ds models, or just with Amalthea?
If you have marsmoons.ssc installed, you should be able to go to Phobos, and see various prominently visible craters labelled - if there's a mismatch there, too, this'll confirm that there's something wrong about the way 3ds locations are displaying on your system.

Grant

[granthutchison]

Bob?
Is it possible you've copied across a definition of Amalthea from a previous version of Celestia's solarsys.ssc? This might account for your problem, since the model has been reorientated between 1.3.0 and 1.3.1. Please check your Amalthea definition and see if it matches the one below, which is the current version:

Code: Select all

"Amalthea" "Sol/Jupiter"
{
   Texture "amalthea.*"
   BlendTexture true
   Color   [ 0.5 0.12 0.16 ]
   Mesh "amalthea.3ds"
   Radius    134 # maximum semi-axis
   MeshCenter [ 13.616 -0.448 4.436 ]

   EllipticalOrbit
   {
   Epoch      2452583.763194445 # 2002 Nov 5 06:19UT (Galileo encounter)
   Period          0.49817905
   SemiMajorAxis   181994.98
   Eccentricity    0.0046637841
   Inclination     0.39217201
   AscendingNode   224.4139186
   ArgOfPericenter 293.4707817
   MeanAnomaly     319.3794140
   }

   Orientation   [ 180 0 1 0 ]
   Obliquity        0.0
   RotationOffset      252.1

   Albedo          0.06
}

Grant

[Bob Hegwood]

Bob?
Is it possible you've copied across a definition of Amalthea from a previous version of Celestia's solarsys.ssc?

No... I had this problem on Pre11 too. By the way, the Mars Moons locations look okay. Maybe I just don't know what I'm looking for? At any rate, a picture is worth a thousand words right?



Does this explain?

Thanks, Bob

[granthutchison]

Ah. Your texture and your model are mirrored relative to each other in some way - are they both the original Celestia versions, or have you substituted a texture or model from some other source? I've seen this texture-mirroring with 3ds models that look OK in the original modeller but misbehave in Celestia.
In the view you provide, are you looking down on the north pole of Amalthea, with Jupiter off the bottom of the view? If so, the model and locations are probably correct, but the texture seems to being mirrored both N-S and E-W, as if it were being applied to the inside of the model rather than the outside. The central greenish albedo feature belongs at the south pole, within the crater Gaea. The crater on the right edge of your picture should actually be on the left.

Grant

[Bob Hegwood]

Grant,

The image above was produced using Rassilon's Amalthea Package as I described it in an earlier post.

HOWEVER - This is almost exactly the same result I got using the amalthea.jpg and amalthea.3ds objects which came with the latest version of Celestia.

Let me play around with it some more to see what's going on here.

Thanks once again for the EXCELLENT information and helpful advice.

Take care, Bob

[granthutchison]

OK, solved (I think).
The texture you downloaded from Rassilon's site is both outdated and wrongly orientated - mirror it top-to-bottom and then shift it in longitude by 180 degrees, and all should be well (compare it to the Celestia original to be sure, though!)
There used to be a bug in how Celestia laid textures on to 3ds models, which had to be compensated for by a N-S mirror in the textures. When the bug was fixed, we were able to unmirror our textures. This old texture of Jens' (which Rassilon is hosting) is still orientated with the mirror-flip required for Celestia 1.2.5 or thereabouts. It's also been prepared from the same Phil Stooke shaded relief map that Celestia uses - but Stooke had 180 degrees as his central meridian, and Jens doesn't seem to have corrected this before applying it to the Amalthea model.
It really is very worthwhile comparing any texture to the Celestia original before using it ...

Grant

[Bob Hegwood]

Grant,

Thanks again for the advice. I simply flipped the image from left to right - and did the same thing from top to bottom - and the image appeared as it should have.

I'm *still* confused by all this though. My JupiterTour.cel script is doing strange things when it gets to Amalthea.

I have restored the original Amalthea texture and model, but when the script MARKS the "Pan" location for example, the location it marks is in a place that's different from the location identified by your "jupmoons.ssc" file.

This is driving me NUTS! The only way the location can be identified is by using the location file, and the location file is showing me two different locations for Pan. In other words, the LABEL "Pan" shows up in a different location from where the script tells the program to mark an "X."

I've looked to make certain that there are no other references to Pan in my "Extra" directory, and that there are no other references to it within your "jupmoons.ssc" file.

Boy, oh boy! I think I need a drink.

Take care, Bob

[granthutchison]

Thanks again for the advice. I simply flipped the image from left to right - and did the same thing from top to bottom - and the image appeared as it should have.

Bob, it still doesn't sound like you've got it quite right, although the result from the above will be an improvement on what you had before. You need to flip top to bottom, but slide through 180 degrees of longitude, as we've discussed from previous textures.

I'm *still* confused by all this though. My JupiterTour.cel script is doing strange things when it gets to Amalthea.

Yes, this is a residual bug in the behaviour of 3ds objects. The coordinates I give in the locations file have to be 180 degrees rotated in longitude relative to their true coordinates in order for them to display correctly on the surface of 3ds objects. It's a bug I mentioned to Chris a while back, and he thought it might have something to do with the configuration of the 3ds's themselves (rather than how Celestia handles them), but so far I've been unable to produce a 3ds that behaves consistently in Celestia.
The true coordinates of Lyctos facula are 20S 120W. So I have to give the coordinates to Celestia as -20, -300. Unfortunately, it sounds like when these are handed back to Celestia in a script it goes to the correct location corresponding to those coordinates - that is, 180 degrees away from where the location has been plotted.
When I select Lyctos facula and go to it, I end up on the other side of Amalthea. But if I select Goto Object from the Navigation menu and go to -20, -120 (Lyctos' true location), I end up in the correct place. I know absolutely nothing about Celestia scripting, but is there any way you can exploit Goto Object to take you to the correct place, without using the name of the location?

Grant

[Bob Hegwood]

Grant,

We can GET to the appropriate location on the moon by using the gotolonglat command and simply plugging in the appropriate coordinates. THIS I can do with no trouble. I'm simply handing the same coordinates in your jupmoons.ssc to Celestia's gotolonglat command.

The problem is that the SAME coordinates are used to MARK the location - as are used by Celestia to place the LABELS on the object.

I just don't GET it. If I go to Io and place a mark on the moon, it shows up in EXACTLY the same spot as does the location label. This simply DOES NOT WORK on Amalthea though. No matter what I do, the marks show up wherever they damned-well please.

Sorry, but this has been causing me grief ALL DAY!

That's okay though, I'll figure it out, or I'll simply get RID of the offending markers, and tell people what weird place Amalthea is.

Thanks again, sir. Boy, you must not have a life either!

Take care, Bob

[granthutchison]

I just don't GET it.

Like I say, it's the 3ds bug thing. The "mark" command takes the longlat coords literally, just as "going to" the location does - each mark you place on a select location ends up 180 degrees of longitude away from where it should be. The coordinates I've been forced to use to place locations on 3ds's properly is misleading other Celestia routines.
I've messed around for quite a while trying to create 3ds objects that behave consistently in this respect, but I can't seem to do it - I'm beginning to suspect it's a bug in the Celestia code, rather than an oddity of the objects themselves ...

Grant

[Bob Hegwood]

Grant,

I think I'll take this topic to the Bugs Forum, where it belongs, but THANKS again for the information...

By the way, you were right about the Central Meridian in Rassilon's texture. I fixed it, and got the correct image map for Amalthea.

This STILL doesn't do me any good though. There is definitetly a bug involved here somewhere.

I'm also going to take a look at using the Lua Celx language to do my scripting. My current approach is way too frustrating.

Take care, Bob

[selden]

Bob,

As a workaround until the problem is fixed, you might want to consider using an AltSurface Texture image of your own that has markers drawn on the surface right where you want them.

Unfortunately, only the Texture declaration itself works for 3DS models. The modifying textures (like NightTexture and OverlayTexture) don't get applied.

[Bob Hegwood]

Selden,

You're missing the point here...

I want the MARKS to appear at a specific time, and then to disappear when I tell them too.

Have a look in the bugs forum for more on this topic: http://www.shatters.net/forum/viewtopic.php?t=4038

Thanks, Bob

[selden]

No, I understand: that's why I said it was a "workaround" -- they usually don't work as well as a fix. It requires turning on the AltSurface that has the marks on it when you want to see them, and then returning to the Normal surface when you want them to go away.

setsurface { name "Marked" }
setsurface { name "Normal" }

Unfortunately, this workaround can't work for Amalthea:
Celestia doesn't draw AltSurfaces on 3DS models.

Sorry.

[granthutchison]

Unfortunately, this workaround can't work for Amalthea:
Celestia doesn't draw AltSurfaces on 3DS models.

Yes it does - the limit of knowledge texture for Hyperion uses AltSurface. What it doesn't do is allow overlays, so we had to build a pair of alternate surfaces, just as you describe, instead of creating a simple LOK overlay.

Grant

[selden]

Grant,

Sorry: you're right.
I tested Overlays and rashly assumed that since they didn't work other forms of AltSurface didn't either.

Thanks for the correction!