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I've been meaning to pick-up some DCG tools. Sadly, I procrastinate...
I do have Inagoni's Veloute but it doesn't seem to work -- and that procrastination thing means that I haven't sought help for it yet. I suck sometimes... :lol:
Still, I'm really curious to see how your work comes out here. I'm sure it will be stellar (pun intended).
I thought about this too... LOL. Moons and even airplanes cast shadows... I guess the question here is would the size of the sun prevent such a "clean" shadow? Does the ISS cast a visible shadow?
ISS does not cast a shadow on the earth, atmospheric scattering swallows it up, depending on altitude planes will cast a shadow on the ground, difference here is 35k FEET verses 370km (average orbital altitude of the ISS) even my 10K cross section torus wouldn't have much of a shadow if any at all, and if there was one, it would very very hard to see.
I will state that you would probably see a shadow on the Moon, or other airless body,
I thought about this too... LOL. Moons and even airplanes cast shadows... I guess the question here is would the size of the sun prevent such a "clean" shadow? Does the ISS cast a visible shadow?
Okay, trying to get more opinions on this with a google search...
Shadows from the sun (being an "area" light rather than a bulb light) break down into UMBRA and PENUMBRA (and something called ANTUMBRA)
http://en.wikipedia.org/wiki/Umbra
The Umbra is what we would call just a normal shadow ir the darkest part within a soft shadow.... The Penumbra is what we would call the shadow falloff, or the edges of a soft shadow.... The part where the shadow edges overlap and cancel out the full Umbra is called the Antumbra (see diagram at the link)....
So the factors involved are:
1) size and distance of the sun (in sci-fi this can change, so it is important to this discussion)
2) size and distance of the object (plane in the sky: yes.... satellite in space, probably not)
3) (atmospheric dispersion does not play a strong roll, unless of course you have a cloudy day... The shadow still falls on the top of the clouds though...)
According to one reply on a StraightDope.com discussion:
"To have the same angular diameter as the sun, a satellite orbiting at the same altitude as the ISS (350 km) would have to be about two miles across (3.2 km)."
So applying this specifically to my Orbital Ring, the way I was trying to build it with a ring of about 1.25km would NOT cast a shadow... however a ring with a cross-section of 10km would cast a hard shadow.... Any "beads" like in my later experiments would probably cast soft individual shadows....
Here in NYC when the new Time Warner towers went up on the southwestern corner of Central Park, it raised a big stink about buildings blocking the sun over outdoor public areas (not to go too deep into it, the towers were tall enough to cast a shadow over an ice skating rink as the sun set, cutting primetime sunlight hours in Winter when the rink would be open). The compromise was to make two towers that were cut along an angle to create a thinner shadow. See pic: http://en.wikipedia.org/wiki/File:Time_Warner_Center_II.jpg)
I suggest that in the future if there are mega constructions in space (even a temporary "visiting" structure like a mothership) they would likely NOT be allowed to park in low orbit (definitely not above a city or farm) because planet dwellers would complain about losing their sun... A space battleship (assuming it looks somewhat like a boat, like the Yamato cartoons) would likely have two orientations: a "thin" profile that does not block the sky, and a "wide" profile that would allow attack with more turret guns (called "crossing the T", the ship that shows it's long side has a gun advantage, basically you don't want to go against another ship unless you are in this advantageous position: http://en.wikipedia.org/wiki/Crossing_the_T ).... Even if it's a large station or a city-in-space there would be design advantages to having a "thin" profile that could be oriented to solar wind, meteor showers, attack from other ships.... or even just to avoid uneven surface heating. So we are more likely to see a megastructure that is shaped like a cigar, fish or saucer oriented to cast a thin shadow, than a big cube or a ball....
interesting, so my 10km cross section torus would cast a shadow. a rather large one, it seems... hmm
Thanks for the comment Joe. You're right, the eye is drawn to the brightest part of the image. It's a good thing I already said that the image isn't done yet. ;-) What I'm attempting to do is get the sun rising above the rings of the planet. I would like it to appear as a sunrise with the rings as the "horizon." and the sun about halfway risen.
My goal has always been to use the volumetric clouds as an element of the rings, and because I imagine the camera being so close to the rings I wanted some larger, more visible element to the rings as well, which is why I started by testing the asteroids. The different iterations I'm posting are meant as steps along the way. The camera angle in the last image is by no means the final, neither is the scale and location of the sun.
As I've been playing with the volumetric clouds and their settings, it's come into my mind that they could be good for doing an image of a young star and it's accretion disc.
Actually I really like how the planet surface came out. Very cool. I definitely need to go back through this thread and preserve some of the ideas and suggestions that have been made.
Evil: I don't know what your beef with the volumetric clouds could be. I thought that they really added a lot to asteroid ring in your scene.
Not a beef really, just not happy with the current implementation. Unfortunately it takes so long to render due to the intersections of the clouds that it's hard to get a good idea what's going in an instant.
Ah! Gotcha...that makes sense. I'm looking forward to seeing what you and Holly end up producing here.
If I wasn't busy trying to beat some installation standards into my colleagues, I'm sure I'd be trying to apply the lessons from this thread into a new image myself... :)
I'm just doing this to entertain myself, so no-one get upset with this please (I'm probably jumping the dicussion back a few posts).
For the structure as Rareth describes it, as far as I can work out, the hard part of the shadow would extend out from the median point to 2km, softening to zero over the next 4 or 5 Km, so you would get a very soft line of 12km on the top of the atmosphere. Add atmospheric scattering to that and it really wouldn't register on the planet below when viewed from space. Remember, Earths axis is usually tilted so the atmospheric thickness can vary from 11km upward depending on that tilt.
Viewed from the ground at the exact mid point of the shadow it's a different story. The Sun covers about half a degree of the sky, a 10km ring would cover about one degree. The Sun would be obscured as you looked at it but only for a short time as the whole system proceded around its orbit of the Sun.
Now, if an entire earth like planet were in view, that's a 12600 km diameter but 1.5 times that of actual land surface in view (linearly) due to perspective distortion.
Taking an airless planet, the percentage of land showing the hard shadow is 4/12600, that's 0.032 % linear of the image, or in other words, on a render of 4000x4000, about 1 pixel.
If you wanted to show the softening shadow make that 3 pixels. To factor in perspective compression divide that by 1.5 depending on view angle.
On a planet with atmosphere I will just say that it jars with my expectations to see even a hint of shadow and compresses the scale in the scene a lot to my eyes.
You could say that's just down to me and my expectations.
Holly, what happens if you set soft shadow for a distance light at high quality for the Sun with a radius of about 100ft?
Out of interest here is a vid of the moons shadow on the Earth during an eclipse.
http://www.youtube.com/watch?v=VenATs6mP8U
Change of subject.
I ran the numbers for a Dyson sphere for you.
With a radius out to the the Goldilocks zone, assuming aluminium 10km thick with no geographical structures.
It came to 7.6 x 10^27 metric tons, that's 7,600,000,000,000,000,000,000,000,000 tons.
That doesn't even factor in the gravitational stresses at the poles of the sphere and some way of attenuating the radiation at the inner surface.
With a land area of 2.81 x 10^17 Square Kilometres, 281,000,000,000,000,000 Km^2
Surface area of Earth = 498,759,249 Km^2
So 563,398,073 times the area of the Earth.
Which begs the question of what did they need all that land for?
In the TNG episode Data said that the sphere they found had an area equivalent to 250,000,000 class M planets. So a little bit smaller.
Apologies for the lengthy post, but I rarely get to play with this sort of thing these days.
So did you really need all that analysis to determine that stuff casts shadows? :)
Of course, if you have an atmosphere to disperse light, then it can vary. But it seems pretty obvious that you can, realistically, go from full shadow to no shadow, using whatever artistic license you want, and still be within the realm of realism.
So did you really need all that analysis to determine that stuff casts shadows? :)
Of course, if you have an atmosphere to disperse light, then it can vary. But it seems pretty obvious that you can, realistically, go from full shadow to no shadow, using whatever artistic license you want, and still be within the realm of realism.
Jesus, give it a rest. It was for FUN
Really cool information RoguePilot! I like the view of the moon's shadow on the earth. Very enlightening.
Jesus, give it a rest. It was for FUN
I hear ya'!
Wow. Relax. No need to freak. Didn't you see the smiley face? :)
Anyway, back to the subject....
I think the challenge of looking into a sun rising is that it is, kinda by definition, backlit. Which means there's no light to light the stuff you want to see. So you've gotta cheat a bit with your lights.
And to sidestep the fact that you're looking into a really bright, probably uninteresting light, this is one time I think using a lens flare can add some interest to an otherwise annoying light source.
Here's a lame, and fairly cliched attempt at a star rising over a ring around some gassy planet. I had to add a second light source tilted a bit to illuminate more of the rocks in the ring. And I added some alpha to the rocks' shaders to light would pass thru a bit and illuminate nearby rocks. But it still isn't real satisfactory. Backlighting is real tough to do unless you can figure out some way to convincingly put in some other light sources.
And here's another one. Don't know why, I just did it. Almost kinda Christmas-y or something.
Looks nice so far.
Here's a low res test that's a little closer to what I want. I'm going to render in layers and composite in PS so that I have a little more control of the effects such as the lens flare and the aura. There is a lens flare BTW to add brightness to the sun. I eliminated the streaks because it was annoying.
For fun? ;-) <--- Smiley.</p>
Apologies Joe, no I didn't see the smiley face.
Wasn't paying attention. Nice renders by the way.
Hi Evil,
That's very good. A young planet in the throes of formation. The belt of rock looks so appropriate in that.
That's when you'd expect a lot of small grains and dust too so the aura looks right.
for Niven's Ringworld check out.
http://www.larryniven.net/
It has several images of the Ringworld and links to sites that discuss it in detail. Several of the images were done with CG programs.
The Ringworld RPG has extensive technical notes the Ringworld's dimensions, construction, etc. and was considered official Known Space cannon by Niven. My signed copy got destroyed by Katrina a few years back, but the RPG and the Companion does have a dedicated fan following that has put it in PDF form. The goal was to have the old books available as a PDF download, and they were getting permission from the authors and artists to do that at one time and did get replies back and permission from the ones who replied back.
2 Ringworld compute games were done and you can see a depiction of the Ringworld in them. too.
Also, worth checking out: is the Atomic Rockets site:
http://www.projectrho.com/public_html/rocket/index.php
If you want to try a bit of research, consider Larry Niven's Ringworld. Not as impossibly huge as a Dyson Sphere, but still...
Once you get past the book being a bit dated, the characters are constantly looking at the thing and later exploring it, and then realising they're massively underestimating the scale. That fragile little ribbon looped around the star is one million miles across. The two seas have tiny little groups of islands in them. One looks awfully familiar to the Earthman... then he realises the "map" of Earth is on a scale of one-to-one.
I *think* the soft shadow of the moon in that video is due to PENUMBRA <-- (my new vocabulary word), rather than the dispersion of light by the atmosphere. It is hitting the cloudtops already very "soft" and its soft shadow is much larger(?) than I perceive the atmosphere is deep... I think the penumbra is already large because the moon is very far away from us... But as Joe says, we can do anything we choose for dramatic effect... Shadows are ominous, so depending on *how* ominous might decide how thick or thin the penumbra needs to be... LOL</p>
There I have use my vocab word 3 times so I will remember it... :P
Today instead of the ring I'm starting with a planet... VERY MUCH A WIP: my coastlines seem to fade out rather than being sharp, my "dirt" color is too brown (should be more honey-sand colored), and I need my water to be more algae-green around the coasts.... The clouds are annoying me because I feel It needs SSS but the settings are all a bit obscure and SSS takes too long too render...
Planet sphere, cloud sphere, and a Primivol atmosphere...
But first an an Earth pic (composite image from NASA) for reference... So you can see how far off the mark I am...
Yes, that's right, that's the penumbra.
The moon is further away but at the scales involved the geometry is very similar, basically the Sun is about 400 times further away than the moon and is about 400 times larger, it produces a very similar shadow to a smaller object closer to the Earth. When we're dealing with hypotheticals, made up technology and half assed estimates...meh. Just change the ring to 5Km instead of 10Km and it matches exactly, the penumbra would be the same proportion.
On the planet textures, is there any way that you can sharpen the edges of the effect using a gradient filter to give a more solid feel to the clouds and coastline?
It has a nice painted effect though and could be useful that way.
Holly nice work. I agree with RoguePilot that the clouds and coasts could be sharper, but for a Flash Gordon or TOS Star Trek or retro Sci-Fi vibe, you've got it nailed.
Here's a retro little video tag I did for a local high school's theatre dept. It's inspired by the old RKO tag. The school leased land to a cell phone company and they've built a tower adjacent to the school, which sometimes interferes with their sound system if they forget to use shielded cables. In the video, the tower actually sits above the town (on the model).
http://youtu.be/K9qgGcraH8s
The clouds look more like liquid floating in another liquid (cream in a cappucino) rather than wispy water vapour. Honestly though, I really like the effect - it enhances the other-world aspect when it is not so recognizably Earth-like.
Here's my latest iteration. Much closer on the clouds, but still not quite happy. I'd like to get more of silver lining effect. Also still playing with the sun position and lighting.
I rendered this in three layers. A background layer with the sun, a middle layer with just the planet and it's aura, and a top layer with the clouds, asteroids and planet with shadow catcher applied to act as a mask and provide a shadow.
Evil, that's looking much nicer, but maybe not in the way you intended.
It took me a while after reading your description to figure out which was the sun. It looks like the sun is more like a planet being illuminated from some other source, somewhere off screen at the top of the image. And I think that's because there is no interaction from the light generated by the sun with the particles in cloudy ring. Again, it's all about interaction of objects in the scene in a convincing way.
Maybe have rays formed by the light passing thru the dust particles, kind of like a spectacular sunset thru a hazy mist here on earth. And have the sunlight light up the clouds in the ring with some gorgeous speckled highlights.
But I do like the kinda spooky and heavy effect you have there.
I agree. The light's the same for all three layers, just the sun object is hidden. That's why I think I need to work on the clouds. There's several parameters that I can tweek, it's just getting them to interact the way that I want.
I took the liberty of blending both of your images.
I'm on my old laptop right now (old software, small screen) so I'm a bit limited on what I can see or do, but extracting the lighting info from your first image and layering it onto the second helps bring the sun back. Putting the dust back in over the top of that adds to the haze.
Duplicate the glows with a touch of gaussian blur and it's in the ballpark. I'm sure you can do better with the raw render layers.
Needs some rays like Joe said.
Really love that planet.
I thought about this too... LOL. Moons and even airplanes cast shadows... I guess the question here is would the size of the sun prevent such a "clean" shadow? Does the ISS cast a visible shadow?
ISS does not cast a shadow on the earth, atmospheric scattering swallows it up, depending on altitude planes will cast a shadow on the ground, difference here is 35k FEET verses 370km (average orbital altitude of the ISS) even my 10K cross section torus wouldn't have much of a shadow if any at all, and if there was one, it would very very hard to see.
I will state that you would probably see a shadow on the Moon, or other airless body,
As Holly has said, it's more about the prenumbra than anything to do with atmosphere. But here's an image to help you visualize why..
ISS
As seen from the ground, the ISS is tiny compared to the sun, so it can't cover the sun to make much of a shadow. Technically, there still is a shadow, but it only dims the sun by less than 1%, so it's not measurable. An annular solar eclipse, which happens when the moon is too far away to cover the sun, also has less of a shadow on the earth. (Or a prenumbral lunar eclipse.) In all cases, even a total eclipse, the shadow is still soft, because the sun is not a point source, so there are spots of the earth (or moon) where it is only partly covered. Similarly, even an aircraft at 35K feet will not have a noticeable shadow, but one at 1000 feet will.
The biggest problems with a rail gun are:
1. high G-force during launch. The space shuttle does about 3G for 7 minutes to reach orbital velocity. A rail gun can't do that because it would be too long, and stretch a thousand miles. 3 or 4G is about the limit for a human vehicle for that duration. (fighter jets do 6 or 9G but for a much shorter duration, usually just a few seconds.) Cargo would work, as long as the cargo is in no way fragile. You're probably talking about 50G or more to make the rail a reasonable length.
2. The atmosphere. If a rail gun shoots something at orbital velocity from near ground level, or even a tall mountain, it will instantly hit a wall of air much stronger than what the shuttle has to handle during reentry. Therefore the velocity would have to be much higher to account for the loss while it climbs out of the atmosphere. Therefore more G force. (When the shuttle sees that kind of velocity, it is near the top of the atmosphere, so there's less drag and heating. It doesn't drop down below 80,000 ft until it has slowed WAAYYY down.)
The elevator is a good idea, but needs a very strong cable. We don't have a material that's strong enough yet, but there are some possibilities. (Carbon nano-tubes, if we could make enough of them.) The elevator must go from ground all the way past geosynchronous orbit, (22,000 mi) or it won't work. Anything shorter will just fall back down. As far as it being a "target," the good news is that if the link is broken from the ground, the whole thing will fall AWAY from the earth. But there may be other issues, if it's broken elsewhere.
Arthur C Clarke in "3001" talks about a docking torus much like you have, but it's at 22,000 mi altitude, and connected to the ground by space elevator. That altitude allows it to be connected to the ground, and still move at orbital velocity.
At the altitude you depict, there is a small but definite drag from the wisps of atmosphere at that level. For instance, the ISS (space station) would lose a dozen miles altitude each year, and must use fuel to re-boost to the desired altitude. Without that, it would fall to earth in roughly 10 years. (See ISS altitude graphs. Gradual decline punctuated by frequent reboosts) Adding just 100 miles altitude would extend that orbital lifetime to about 500 years. (In the case of the ISS, it's not worth it because the shuttle and other ships would have to use much more fuel to reach it.)
There is also a concept for a smaller structure called a skyhook. It's a long tether, but not as long as a space elevator. It rotates so each end dips down into the atmosphere several times per orbit. While the tip is down, it's velocity approaches zero, so it is easy for an airplane or similar vehicle to latch onto it. As the tip rotates around, the far end whips the vehicle into orbital velocity.
I think I figured out an excuse to have the ring... It spins FASTER than its orbit, to provide an artificial gravity. It has to be a ring because it is held together like a suspension bridge, held in shape like a cowboy lariat.
Would that work? :)
I only picked the ISS because I had originally thought the ring would be geostationary, but then when I saw the ISS orbit it looked more dramatic, plus there are endless reference videos on youtube of what the Earth looks like from that distance... Anyway it seemed like a good starting point.
I think I am officially in LURV with this plugin! LOOK! OUR OLD WORLD HAS CRASHED AND BURNED, BUT WE FOUND A NEW HOME... IN SPACE...