Celestia Forums

http://planetarynames.wr.usgs.gov/index_images.html

http://planetarynames.wr.usgs.gov/images/Titan_comp.pdf

http://planetarynames.wr.usgs.gov/image ... daries.pdf

UPDATE

Lots of new lakes named . . . It looks like we need to update the Titan locations. It would also be nice to create an alternate surface map for Titan using all the SAR images.

--Chris

chris wrote:...It would also be nice to create an alternate surface map for Titan using all the SAR images.

--Chris

Here I'd have strong reservations!

While radar imaging has high merits in combination with near IR imaging in the search for lakes, it is NOT a suitable tool for rendering the visual surface appearance of Titan! Since Celestia is UNFORTUNATELY still limited to rendering visual wavelength...

So that task would surely be for someone else and would NOT have my endorsement...

Fridger

t00fri wrote:

chris wrote:...It would also be nice to create an alternate surface map for Titan using all the SAR images.

--Chris

Here I'd have strong reservations!

While radar imaging has high merits in combination with near IR imaging in the search for lakes, it is NOT a suitable tool for rendering the visual surface appearance of Titan! Since Celestia is UNFORTUNATELY still limited to rendering visual wavelength...

So that task would surely be for someone else and would NOT have my endorsement...

But it would certainly be appropriate to include it as an *alternate* surface, would it not? I am not proposing that we should replace the current map, only that we should add a second map selectable via the alternate surfaces context menu. There are many features that are only prominent in the radar imagery (lakes, candidate cryovolcanoes, impact craters.) It would be very educational to be able to switch between the IR map and the IR+RADAR map to see how the surface appears to different detectors.

Jason Perry has a created a nice Titan near-IR map with the SAR swaths overlain on it. All SAR swaths released so far on the PDS are included:

http://pirlwww.lpl.arizona.edu/~perry/RADAR/

--Chris

chris wrote:

t00fri wrote:

chris wrote:...It would also be nice to create an alternate surface map for Titan using all the SAR images.

--Chris

Here I'd have strong reservations!

While radar imaging has high merits in combination with near IR imaging in the search for lakes, it is NOT a suitable tool for rendering the visual surface appearance of Titan! Since Celestia is UNFORTUNATELY still limited to rendering visual wavelength...

So that task would surely be for someone else and would NOT have my endorsement...

But it would certainly be appropriate to include it as an *alternate* surface, would it not? I am not proposing that we should replace the current map, only that we should add a second map selectable via the alternate surfaces context menu. There are many features that are only prominent in the radar imagery (lakes, candidate cryovolcanoes, impact craters.) It would be very educational to be able to switch between the IR map and the IR+RADAR map to see how the surface appears to different detectors.

Jason Perry has a created a nice Titan near-IR map with the SAR swaths overlain on it. All SAR swaths released so far on the PDS are included:

http://pirlwww.lpl.arizona.edu/~perry/RADAR/

--Chris

Alternative maps can almost contain anything... But as to Celestia, we are still stuck with a tiny window of wavelengths (visual or near visual) .

Open that window and I will be HAPPY! I have given up beating dead horses long ago


Fridger

Time to implement filters?

ElChristou wrote::D Time to implement filters?

My God, YES Even Microsoft has them meanwhile (before us, despite my early advocating...)

chris wrote:Lots of new lakes named . . . It looks like we need to update the Titan locations.

Symaski62 is being typically telegraphic, so maybe I'm missing something ...
But the lake names on his map date from September last year, and the mare and insula from April this year. They're all present in saturnmoon_locs.ssc as of April. My announcement of the lakes update is six months old, here.

(Thanks, by the way, for picking up the subsequent miscoding of Mayda Insula: I seem to have a bug in my macro )

Grant

ElChristou wrote::D Time to implement filters?

I don't think that it's appropriate here. We simply want to give the user the choice of two different maps of Titan: the near-IR methane window, and the near-IR map with the SAR swaths. Choosing one view or the other is very simple: you select the map you want from the surfaces menu. I think that in this case, a filters mechanism would force a users to work a lot harder to get the view that they wanted. In addition, the SAR swaths cover only a very limited fraction of Titan's surface, so having the the near-IR data in background is quite helpful. With a filter-based approach, presumably you'd see just the radar data. One could design a very flexible filter scheme that would allow the user to configure things to see a window extending from the radio spectrum to near-IR and thus see everything. But, that's a large burden for a user who just wants to see the SAR swaths.

Keep in mind that that there are bigger differences between the SAR and near-IR images than just wavelength. SAR stands for Synthetic Aperture RADAR--Cassini's SAR imager measures the reflectance from Titan's surface of a radio signal emitted by the spacecraft, whereas the near-IR images are of radiation emitted by the Sun. Cassini's RADAR sensing instrument can also operate in passive mode, measuring radiation from natural sources that is reflected from Titan. I think that this is more similar to the way the visible and near-IR imaging works. The instrument has quite different characteristics when operating in passive mode--note the vastly reduced resolution of passive vs SAR: http://saturn.jpl.nasa.gov/spacecraft/i ... -radar.cfm This suggests to me that it may be even be misleading to simply drop in the SAR map of Titan and show it whenever the user chooses to observe in a frequency range that overlaps the RADAR's 13.87 GHz band. Much better to give the user a choice of two (or more) maps, one labeled clearly and accurately "Near-IR with SAR overlay."

--Chris

granthutchison wrote:

chris wrote:Lots of new lakes named . . . It looks like we need to update the Titan locations.

Symaski62 is being typically telegraphic, so maybe I'm missing something ...
But the lake names on his map date from September last year, and the mare and insula from April this year. They're all present in saturnmoon_locs.ssc as of April. My announcement of the lakes update is six months old, here.

My apologies, Grant. I'd forgotten about this and thought that the only named (apparent) liquid features on Titan were Kraken Mare and Ontario Lacus.

--Chris

chris wrote:I don't think that it's appropriate here...

I understand, was just that soon or later filters will have to be implemented, so as we need a reason to start, I thought it was perhaps a good one... (unfortunately I was wrong! )

Chris wrote:We simply want to give the user the choice of two different maps of Titan

Who is we besides yourself ?

Fridger

As best I can tell, WWT does not have wavelength filters. It just lets you select different named datasets. For example, select 2MASS [not WMAP as I typed previously] to see the sky in infrared. Am I overlooking something?

Of course, Celestia already does this for SSC objects using AltSurface, as Chris pointed out above.

If the Viewable operator were implemented for STC and DSC objects, this type of selection could be done for deep space objects, too.

chris wrote:My apologies, Grant. I'd forgotten about this and thought that the only named (apparent) liquid features on Titan were Kraken Mare and Ontario Lacus.

No apologies necessary.
You have a lot to keep track of, and I've long since given up cluttering the developers' list with my updates to the data files. I restrict myself to forum announcements concerning updates that people might find interesting: new moons, new names for moons and KBOs, extrasolar planets that have hit the news, and major additions to the locations files.

Grant

selden wrote:As best I can tell, WWT does not have wavelength filters. It just lets you select different named datasets. For example, select 2MASS [not WMAP as I typed previously] to see the sky in infrared. Am I overlooking something?

Of course, Celestia already does this for SSC objects using AltSurface, as Chris pointed out above.

If the Viewable operator were implemented for STC and DSC objects, this type of selection could be done for deep space objects, too.

Selden,

but that's effectively using a wavelength filter, isn't it? In 2MASS, for example, the IR filter was applied when the data were taken. Effectively, as concerns Celestia or WWT, this seems to be the only practical way of visualizing different wavelength windows...
The only "eye candy" one might add at the software front is a slider that allows to blend smoothly various images photographed in different wavelength windows.

I am surely aware that adding-in SAR swaths to near IR Titan imaging effectively amounts to that philosophy. My plea is to contemplate AT LAST a systematic approach to what I advocate since years and years, rather than allowing for a particular exception only in case of Titan...

Fridger

Um... of curiosity, if Celestia is to only display visible light wavelengths, what should we use for the maps of Titan and Venus? Don't both of their maps rely on radar wavelength data?

Hungry4info wrote:Um... of curiosity, if Celestia is to only display visible light wavelengths, what should we use for the maps of Titan and Venus? Don't both of their maps rely on radar wavelength data?

Indeed...
A very good question...
There are many interpretations of what the human eye might see available on the ML, and on CM, but these are also fictional to some extent too. Are they not?
In my case, I use John' van Vliet's interpretations as they seem to be more realistic to me, but that really doesn't mean that they are realistic. In fact, I can not even tell you
what the Venus texture shipped with Celestia even looks like, because I have never used it.

Hungry4info wrote:Um... of curiosity, if Celestia is to only display visible light wavelengths, what should we use for the maps of Titan and Venus? Don't both of their maps rely on radar wavelength data?

Indeed, Titan is a bit of a special case. Yet, it's about consistent with the present "visual light" philosophy. From above Titan's atmosphere, in visual light (RGB filters) mainly the orange smog is seen.

(Cassini mission photo, http://photojournal.jpl.nasa.gov/jpegMo ... modest.jpg)

That's also what Celestia shows if the atmosphere is ON.

But since in Celestia (not in reality!) we have a key to switch OFF the atmosphere, in such "virtual" case the naked eye would see what was obtained by using near-infrared imaging for penetrating the smog.

Unlike radar wavelengths (SAR <-> 2.2 cm!!!), near-infrared is much closer to the visual range, such that we can still infer the rough structure of visual surface details in absence of the Titan atmosphere. The orange colour of my texture is NOT the true surface color but rather the color of the skylight that penetrates the smog to the surface.



Fridger

All of these renditions are still trying to follow the inherent Celestia philosophy are they not?
It's just that we still lack reliable data for some of these objects. Yes? As long as the aim is to get to what is as realistic as possible, then I'm happy.

Right now, Venus is my own personal pain in the Wazoo because, although it has been demonstrated that there are gray portions of the surface (as seen from reprocessed Venusian lander images)
I can also point you to reputable scientific sites which describe the surface of the planet as being ("brown and reddish") in color. How does one choose the appropriate conditions for rendering in Celestia
when even the so-called "experts" disagree with each other concerning what the human eye would see? This is really perplexing, at least to me. Also, no one can tell me what effect the Venusian atmosphere has on our perceptions of the planet's surface.

However, as long as a good-faith effort is maintained to get to the bottom of these things, I am very happy with Celestia's approach to the rendering of the planets and moons. I must say that here, I agree
completely with the Good Doctor Schrempp, and his philosophies. He, at least, has the scientific background and knowledge in order to make educated decisions as to what the planets should look like.

Also, he is completely honest, and I think that this quality (more than any other) should be encouraged.

BobHegwood wrote:All of these renditions are still trying to follow the inherent Celestia philosophy are they not?

Yes, that's what I meant to say.

It's just that we still lack reliable data for some of these objects. Yes? As long as the aim is to get to what is as realistic as possible, then I'm happy.

Right now, Venus is my own personal pain in the Wazoo because, although it has been demonstrated that there are gray portions of the surface (as seen from reprocessed Venusian lander images)
I can also point you to reputable scientific sites which describe the surface of the planet as being ("brown and reddish") in color. How does one choose the appropriate conditions for rendering in Celestia
when even the so-called "experts" disagree with each other concerning what the human eye would see? This is really perplexing, at least to me. Also, no one can tell me what effect the Venusian atmosphere has on our perceptions of the planet's surface.

However, as long as a good-faith effort is maintained to get to the bottom of these things, I am very happy with Celestia's approach to the rendering of the planets and moons. I must say that here, I agree
completely with the Good Doctor Schrempp, and his philosophies. He, at least, has the scientific background and knowledge in order to make educated decisions as to what the planets should look like.

Also, he is completely honest, and I think that this quality (more than any other) should be encouraged.

Bob,

there is a huge difference between the SAR (radar) data for Titan and Venus:

The older Magellan mission SAR data for Venus used a VERY long radar wavelength of ~13 cm! The much more recent Cassini SAR uses a much shorter one of "only" 2.2 cm. Of course it is still HUGE compared to the near infrared optical wavelength, which is merely used to penetrate the smoggy Titan atmosphere. Moreover, unlike Titan, there was NO significant additional data taking for Venus in the optical regime! Hence an interpretation of these very long wavelength radar data of Venus in terms of real surface features remained very doubtful.

For Titan the near infrared resolution is quite OK for surface imaging, while still being reasonably close to visual wavelengths. Hence here SAR imaging was mainly used as complementary hires tools in the search for lakes and other novel structures. (Since radar data are good in distinguishing smooth from rough terrain...)

Fridger