Celestia Forums

Interesting new pictures of Dione are starting to appear at the Cassini website (http://saturn.jpl.nasa.gov/multimedia/images/raw/index.cfm).

- Hank

http://saturn.jpl.nasa.gov/multimedia/images/raw/raw-images-details.cfm?feiImageID=28993

c.f.

cel://PhaseLock/Sol:Cassini/Sol:Saturn:Dione/2004-12-14T16:45:04.73309?x=e4oQQTGwZ4OGDA&y=0fc53jiBH+v//////////w&z=ptHJbsxS7/17/////////w&ow=0.901498&ox=0.343779&oy=-0.262878&oz=0.003627&select=Sol:Saturn:Dione&fov=0.361300&ts=-0.100000<d=0&rf=104343&lm=0

Wow, looks like the wispy terrain really was like the Bright Terrain on Ganymede... or actually more like Ariel given that's the same sort of size as Dione - looks like rift valleys and extensional faults.

VERY interesting...

(I like images of satellites that I can make sense of. Titan meanwhile has everyone still scratching their heads...)

I had always wondered if the wispy stuff actually wasn't faulting. Still, I was kind of hoping for some sort of active geological process.... But the number of craters would seem to bely that.

This IS neat!

...John...

Could this raw images enough to prerpare a 4k texture of Dione?Or are we going to wait until 2005?
The image in Celestia is very crude and devoid of details

danielj wrote:Could this raw images enough to prerpare a 4k
texture of Dione?Or are we going to wait until 2005?
The image in Celestia is very crude and devoid of details

I disagree:

below I compare the 'dione.jpg' from Celestia CVS [Old] with the
one we have so far from from Cassini [New]. The old one is from
24 years ago (!) (from Voyager 1, 1980), but the amount of detail is
still higher than on the present Cassini image [New]:

Bye Fridger

The old one is from 24 years ago (!) (from Apollo 1, 1980)

Voyager 1, you mean.

The Apollos were the manned flights to Earth orbit and the moon in the 1960s and 1970s.

You didn?t understand,Fridger.
This map is set before the close flyby of Cassini of December 13.
The closeup images show much more detail,but they are raw

danielj wrote:You didn?t understand,Fridger.
This map is set before the close flyby of Cassini of December 13.
The closeup images show much more detail,but they are raw

Of course, I understood and correspondingly phrased
my post carefully:

so far we are lacking the required data (about the
viewing parameters) to do a cylindrical projection from
the recent hires photos. Therefore, what I showed is all
that is available for the moment. Correct?

...and unlike what you stated above the amount of detail
in the 24 year old Celestia Dione texture is not so bad at all!

Bye Fridger

Just for fun

I've build this little mosaic of 4 raw images.



link to highres picture ( 345 kB )
http://www.celestiaproject.net/~jim/images/dione1.jpg

Bye Jens

added later:
It's seems that somebody had the same idea.
http://photojournal.jpl.nasa.gov/catalog/PIA06163

jim wrote:Just for fun

I've build this little mosaic of 4 raw images.



link to highres picture ( 345 kB )
http://www.celestiaproject.net/~jim/images/dione1.jpg

Bye Jens

Hey Jens,

that is fun, indeed! If we knew the viewing angles, I could do the cylindrical projection...Anyway, I'll look into it...

Bye Fridger

so far we are lacking the required data (about the
viewing parameters) to do a cylindrical projection from
the recent hires photos.

Perhaps Daniel doesn't quite appreciate what needs to be done to make a cylindrical map. To reproject the images - and basically you're going from orthographic (a spacecraft view of a globe) to simple cylindrical (flat map that can be projected onto a globe) projection - you need to know the camera angles, and you also need to know where the match points are on the separate images that make up the image, or each image in the mosaic will overlap in the wrong places when you reproject it. It's a somewhat complex process.

The full-blown scientific way to do it is described on the ISIS pages, ISIS being the USGS planetary image processing software which I have spent far too much of my life working with . You have to go through other steps like tidying up the image labels, correcting the spacecraft pointing data, calibrating the images so that you remove camera distortions, adjusting for photometry etc before you get a scientifically accurate and usable mosaic.

Currently we don't have the camera pointing data so it's not possible to make an accurate mosaic. One could probably do an inaccurate mosaic by 'feel', but it would be very time consuming and not very rewarding.

Wouldn't it be possible to derive the mapping function mathematically if you knew the mapping for three specific points?

- Hank

hank wrote:Wouldn't it be possible to derive the
mapping function mathematically if you knew the
mapping for three specific points?

- Hank

Hank,

yes, I think there a quite are a few things that one
might /impatiently/ do along the lines you
mentioned . I was also thinking to qualitatively read
off the viewing angles from the Celestia simulation of the
encounter. As I have discussed in 'users', the
approximation is surprisingly good.
The distances for the above photos have been given
rather accurately and the diameter of Dione is also pretty
well known.

Yet the question arises: is it worth these rather tedious
efforts? I tend increasingly towards a "data clean"
approach for the Celestia distribution, in the sense that
we should refer to published/official sources as much as
possible. This naturally also includes textures. In case of
Titan, Nasa has already produced a cylindrical
projection. I am sure they will update it pretty soon.
Probably, they will also come up with a Dione texture in
the near-future.

Bye Fridger

Fridger,

On the Cassini site there is a map of Dione showing the areas to be imaged during the recently flyby, based on more distant Cassini imaging obtained earlier in the mission. As far as I know, this earlier Cassini-based map of Dione has never been released publicly. Maybe someday, but who knows how long? The Cassini site also has images of a topographic map painted on a shape model of Phoebe. Those images were released in July, but the actual shape model and topographic map still have not been released, as far as I know. I'm afraid that if we have to wait for NASA to release their formal data products, it could be a long wait. Certainly we should take advantage of them when they do become available, but in the meantime I think it would be nice to have some less accurate but still useful interim models and textures derived from whatever data we have.

- Hank

hank wrote:Fridger,

On the Cassini site there is a map of Dione showing the
areas to be imaged during the recently flyby, based on
more distant Cassini imaging obtained earlier in the
mission. As far as I know, this earlier Cassini-based
map of Dione has never been released publicly. Maybe
someday, but who knows how long? The Cassini site
also has images of a topographic map painted on a
shape model of Phoebe. Those images were released in
July, but the actual shape model and topographic map
still have not been released, as far as I know. I'm afraid
that if we have to wait for NASA to release their formal
data products, it could be a long wait. Certainly we
should take advantage of them when they do become
available, but in the meantime I think it would be nice to
have some less accurate but still useful interim models
and textures derived from whatever data we have.


- Hank

Hank,

of course --being impatient myself -- I sympathize
with what you suggest. So with the holidays ahead of us,
perhaps I'll have a go at it...


The result will certainly be better than what we have so
far.

Bye Fridger

How long it will be before officially produced maps are released depends largely on when the full raw data is released (including headers with accurate pointing data) and when the public release of ISIS is capable of processing cassini images.

I'm guessing the full raw data set will be released 6 months to a year after the images from each flyby are received, if Galileo was anything to go by. After that, someone would need to actually process the images to make the maps, which can be rather time consuming.

In other words, don't hold your breath

t00fri wrote:

hank wrote:Fridger,

On the Cassini site there is a map of Dione showing the
areas to be imaged during the recently flyby, based on
more distant Cassini imaging obtained earlier in the
mission. As far as I know, this earlier Cassini-based
map of Dione has never been released publicly.[...]

of course --being impatient myself ;-) -- I sympathize
with what you suggest. So with the holidays ahead of us,
perhaps I'll have a go at it...

The result will certainly be better than what we have so
far.

The interesting thing to me is that that map claimed to be based on Cassini data looks strikingly similar to the Schenk photomosaic on the Planetary Society Dione page (scroll to the bottom) that was produced from Voyager imagery: the variations in resolution and the coverage boundaries are mostly the same, the major difference being more coverage in the polar regions on JPL's map. I suspect that JPL's map is not entirely made from Cassini data but is actually a Voyager-Cassini composite, which makes sense given that I think much of the Voyager data was actually better than Cassini's at the time the map was made.

The USGS map used for the Celestia distribution texture (and Jens's excellent high-res .dds) was an interpretation of the same Voyager images that Schenk used. All things considered, it's not bad. But it looks to me as if it emphasized topography rather than albedo features, and that a couple of the fainter streaks that USGS put east of Padua Linea may even have been erroneously extrapolated from the low-res pictures, since the Schenk photomosaic in that region looks more like the Cassini pictures than the USGS map does.

From CARTOGRAPHY OF THE ICY SATURNIAN SATELLITES:

"The Cassini spacecraft is preparing to enter orbit about Saturn on July, 1st, later this year, and will then carry out a comprehensive exploration and mapping program of its icy satellites. Motivated by these future prospects, we are presently carrying out a comprehensive photogrammetric and cartographic study of these satellites, using images obtained by the Voyager-1 and -2 spacecraft during their Saturn flybys in 1980 and 1981... We have re-measured control points and re-computed a control point network for Saturn's satellite Dione. Our network is based on16 images (obtained by the narrow-angle cameras of Voyager I and II), 135 control points, and 741 point measurements. We obtained mean point accuracies of 1.8 km, 2.9 km, and 1.2 km for X, Y, and Z, respectively. The radius of Dione was re-determined to be 562.5 km +/- 0.2 km with a RMS deviation of 3 km, consistent with 560 km (RMS: 5 km) found by Davies et al. 1983. Subsequently, we generated a sequence of controlled digital base mosaics for the five (among the largest) satellites Mimas, Enceladus, Tethys, Dione, and Rhea... Both, map projection and mosaicking software, originally developed at DLR (Scholten, 1996), are currently improved for the upcoming data processing of the Cassini-ISS images.These digital image mosaics will be released in PDS format."

This very interesting report includes a map showing the coverage of Dione at various resolutions expected to be obtained by Cassini in 2004-7.

- Hank

There is something interesting on the surface of Dione which is being debated over at Badastronomy now; these images are twenty five years apart, but both show a very similar streak; the streak in the 2004 image seems incredibly straight, and very like an imaging artefact, but seems to be present in the old pic too.

http://tinypic.com/z4c4p

http://tinypic.com/z4dg7

hmm; now I examine the images together, the relationship between the streaks seems less compelling. Oh well; there you go.

It doesn't look like an imaging artifact to me.

- Hank