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Bill Pragnell nous apporta ses lumieres en ce 2005-10-26 12:26:
> Alain <ele### [at] netscape net> wrote:
>
>>Needs an area_light. In all the ilustrations I saw, the shadows have soft edges.
>
> I have a feeling that soft terminators would not be visible on the arch to
> the naked eye - too small. It's likely that Ringworld illustrations are
> exaggerated for artistic effect.
>
> I could be wrong - I *think* I used an area_light for my ringworld picture
> (see previous thread) but I can't remember! :)
>
> Bill
>
In the images I saw, the shadowing squares are between 1/2 and 2/3 of the ring's
radius. With such
proportions, you have prety whide penumbraes.
--
Alain
-------------------------------------------------
To the world you may be one person, but to one
person you may be the world.
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"Alain" <ele### [at] netscapenet> schreef in bericht
news:43603cc3$1@news.povray.org...
> >
> In the images I saw, the shadowing squares are between 1/2 and 2/3 of the
ring's radius. With such
> proportions, you have prety whide penumbraes.
>
According to Larry Niven, in Ringworld, the shadow squares are 1x10^6 by
2.5x10^6 miles big, and orbit the sun at about 12x10^6 miles from the
primary. Now, this last figure seems to be wrong. According to my building
in Moray, they should orbit at about 16x10^6 miles so that day and night
areas are about the same size.
An area light for the sun is needed indeed. I used a glow (for latter
purposes), but I shall experiment further.
Larry Niven is not talking about a penumbra area in his books, as far as I
can tell. Night comes with the sun gradually cut-off by the shadow square.
Which doesn't exclude a penumbra of course.
Thomas
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"Bill Pragnell" <bil### [at] hotmailcom> schreef in bericht
news:web.435f7e721389c621731f01d10@news.povray.org...
>
> That's really good. I think it looks better than anything I managed. I
might
> have to dig out my code - we can have a Ring-off!
>
Thank you! And this is just a quick construction without any sophisticated
stuff!
> One point, however: to my mind, the shadowed areas of the arch should be
the
> same colour as the sky - just like the shadowed areas of the moon in our
> sky during daylight. The lit areas of the ring would probably not cast
that
> much light - certainly less than the earthlight cast onto the moon.
>
I agree. And Larry Niven imlies that the arch is invisible during daylight.
In my scene the arch is visible because there is no real atmospheric haze in
this scene, so the arch is viewed as if there were no atmosphere at all. The
blue sky here is faked. But this is the next step to solve indeed.
> Otherwise, keep 'em coming!
>
Hope to!
Thomas
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"Alain" <ele### [at] netscapenet> schreef in bericht
news:43603cc3$1@news.povray.org...
> >
> In the images I saw, the shadowing squares are between 1/2 and 2/3 of the
ring's radius. With such
> proportions, you have prety whide penumbraes.
>
What I forgot to say is that the Ringworld radius is 95x10^6 miles. This
means that the shadow squares are very close to the sun in comparison to the
Ringworld.
Remember the chapter about the shadow squares when Lying Bastard drifts
helplessly against the shadow square thread: it is very, very hot!
Thomas
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Wasn't it Thomas de Groot who wrote:
>
>Larry Niven is not talking about a penumbra area in his books, as far as I
>can tell. Night comes with the sun gradually cut-off by the shadow square.
That's exactly what a penumbra is. An observer standing in the penumbra
sees only part of the sun, the other part being cut off by the edge of
the shadow square. So the amount of light striking such an observer is
reduced.
--
Mike Williams
Gentleman of Leisure
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This is a much more dramatic image, I believe.
I used an area_light, the size of the sun; I placed the camera *near* one of
the rim walls; I reduced the camera angle to 75 degrees (earlier it was to
large).
Dimensions are almost meaningless on the Ringworld! In this scene, we are at
100 miles altitude, and still 10000 miles from the rim wall! Note however,
how the arch takes a more interesting shape in this view.
Thomas
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Attachments:
Download 'ringworld_04.jpg' (52 KB)
Preview of image 'ringworld_04.jpg'
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"Mike Williams" <nos### [at] econymdemoncouk> schreef in bericht
news:deR### [at] econymdemoncouk...
> Wasn't it Thomas de Groot who wrote:
> >
> >Larry Niven is not talking about a penumbra area in his books, as far as
I
> >can tell. Night comes with the sun gradually cut-off by the shadow
square.
>
> That's exactly what a penumbra is. An observer standing in the penumbra
> sees only part of the sun, the other part being cut off by the edge of
> the shadow square. So the amount of light striking such an observer is
> reduced.
>
Yes indeed, I stand corrected. Furthermore, Niven tells in fact how the
sunlight is reduced during the transition to night. My impression was
however, that it occurred pretty quickly.
Thomas
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"Thomas de Groot" <t.d### [at] internlnet> wrote:
> This is a much more dramatic image, I believe.
Very much so! Very nice.
> I used an area_light, the size of the sun; I placed the camera *near* one of
> the rim walls; I reduced the camera angle to 75 degrees (earlier it was to
> large).
I've been having problems with the rim walls. They are described as
mountains in the book; but I can't think of an easy way to implement them.
Sloping or curved walls are no problem, but texturing them is another
matter...!
How many shadow squares are you using? They look a bit different to mine...
Bill
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"Bill Pragnell" <bil### [at] hotmailcom> schreef in bericht
news:web.43609d6881b06728731f01d10@news.povray.org...
>
> How many shadow squares are you using? They look a bit different to
mine...
>
According to Niven, there are 20 shadow squares.
Thomas
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"Bill Pragnell" <bil### [at] hotmailcom> schreef in bericht
news:web.43609d6881b06728731f01d10@news.povray.org...
>
> I've been having problems with the rim walls. They are described as
> mountains in the book; but I can't think of an easy way to implement them.
> Sloping or curved walls are no problem, but texturing them is another
> matter...!
>
Yes, I have been pondering that issue too. I wonder if I shall not try to
make a mesh in Wings or Silo, so that individual areas can be textured
properly. Also, that would give the possibility to carve some mountains in
the rim wall, as well as the topography in the immediate neighbourhood of
the camera, let alone Fist-of-God!
Presently, I am experimenting with media inside a container to simulate the
atmosphere, but not yet really satisfying.
Thomas
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