OK, so I didn't look through all 7598 entries in the 'general' group, but I
think I have an unusual application for POVRay.

I dabbled in rendering complex scenes a few years ago, but since I don't
have the kind of hardware which makes rendering painless and fun, I
switched to modelling Solar Eclipses with POVRay.

While it is a little complex to calculate the positions of the Sun, Moon and
Earth during an eclipse, the calculations pale into insignificance compared
to the actual raytracing.

Anyway, I've only recently put all this onto a live website. You can see it
at:

http://www.pavium.info/Eclipse/

All this is several years old now. Let me know if there's any interest out
there.

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pavium wrote:
> ... I switched to modelling Solar Eclipses with POVRay.
> ...
> Anyway, I've only recently put all this onto a live website. You can see it
> at:
> 
> http://www.pavium.info/Eclipse/
> 

(This reply is definitely OT, but...)

In looking at your website, specifically about the size problem, I was 
reminded of something I read about many years ago.  Now my memory is 
quite imperfect, and this was probably about 40 years ago, so I only 
remember the generalities and not too many details.  It was a 
description of a nature trail somewhere in Europe (I think it was in 
Switzerland), which had a scale model of the solar system along it. 
There was a 6 foot (or probably 2 meter) sphere at the trailhead which 
represented the sun, and at the proper proportional distances along the 
trail were properly scaled models of the planets.  I thought this was 
such a fascinating idea that I've always remembered it.  I think the 
article I read was probably in Astronomy Magazine, or perhaps Scientific 
American -- definitely a magzine of that sort, but I've never seen it 
described anywhere else.  And of course, I have no idea whether or not 
this trail/model still exists.  Anybody else know about it?

      -=- Larry -=-

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"Larry Hudson" <org### [at] yahoocom> wrote in message 
news:44137b78@news.povray.org...
> pavium wrote:
>> ... I switched to modelling Solar Eclipses with POVRay.
>>
>> http://www.pavium.info/Eclipse/
>>
>
> There was a 6 foot (or probably 2 meter) sphere at the trailhead which 
> represented the sun, and at the proper proportional distances along the 
> trail were properly scaled models of the planets.  I thought this was such 
> a fascinating idea that I've always remembered it.
> I have no idea whether or not this trail/model still exists.  Anybody else 
> know about it?

I sure don't know of that one, yet I've heard of such things elsewhere. I 
actually tried a model of the solar system out on my lawn once, had a flat 
grassy yard where I lived before, so I placed a bunch of PVC pipes in the 
ground forming the concentric circles then put pipes with 'blindspot' 
mirrors on the tops (to reflect sunlight) into position to mark where each 
planet was at the time. No correct scale to the distances, though, or else 
I'd never have enough lawn. Also, the gas giant planets, aside from Juptier, 
were basically in the same places every day. Ha ha! And I only did that for 
a couple years. The pulling up and replacing them for each lawn mowing 
wasn't very practical either.  ;)

Back to the eclipse POV scene stuff... Not sure if I'll see the next one 
here or not but will be looking for the penumbral lunar eclipse Tuesday 
morning. Downloaded the file and will see how it does for that one. [editing 
back up to here] {Tried it and I think I'm seeing a shadow on the Earth for 
that partial eclipse, would take me longer to know positively.}

Good writing there on the web site about all that, and the eclipse.pov sure 
is a typical math maze of astro-calc! There are definitely some people out 
there using POV with associations to astronomy. Paul Bourke comes to mind.
-- 
Bob H  www.3digitaleyes.com
http://3digitaleyes.com/imagery/

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Larry Hudson wrote:
> pavium wrote:
>> ... I switched to modelling Solar Eclipses with POVRay.
> 
> In looking at your website, specifically about the size problem, I was 
> reminded of something I read about many years ago.  Now my memory is 
> quite imperfect, and this was probably about 40 years ago, so I only 
> remember the generalities and not too many details.  It was a 
> description of a nature trail somewhere in Europe (I think it was in 
> Switzerland), which had a scale model of the solar system along it. 
> There was a 6 foot (or probably 2 meter) sphere at the trailhead which 
> represented the sun, and at the proper proportional distances along the 
> trail were properly scaled models of the planets.  I thought this was 
> such a fascinating idea that I've always remembered it.  I think the 
> article I read was probably in Astronomy Magazine, or perhaps Scientific 
> American -- definitely a magzine of that sort, but I've never seen it 
> described anywhere else.  And of course, I have no idea whether or not 
> this trail/model still exists.  Anybody else know about it?

I think there are several of those trails in Switzerland, and I'd expect 
many more to exist around the world. One I know is on the Uetliberg in 
Zurich: <http://www.uetlibergverein.ch/planet/index_planet.htm>, 
<http://fiete.ch/Medien/Galerie/11300/113091.html>, 
<http://map.search.ch/uetliberg>. It's at 1:1e9 scale, so the sun is 1.4 
m in diameter.

  -Christian

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Without too much trouble at all I got a rendering made of the eclipse about 
to occur tomorrow night. Just a temporary (however long it exists there) 
upload to my web site since this isn't anything but a test.

http://www.3digitaleyes.com/povray/eclipse.jpg

Since I already had image maps of the earth, clouds, moon here I didn't need 
to go looking for any.

Here's all I did to get the view seen in the picture:

Added 'area_light <1e6,0,0>,<0,1e6,0>, 9,9 jitter' to the Sun light_source 
(yes, that's 1 by 1 million).

Removed the scale 2 for the Moon since this needed the proper size to work 
okay, raised diffuse finish considerably to get more brightening for shadow 
contrast.

Put +y*15000 onto the end of the camera location vector and +y*5000 onto the 
end of the look_at vector.

Changed the date, time.

Of course, I don't think this is completely accurate because I just tried 
numbers for the area light without checking on scales and distances of 
everything. Only a quick try at getting an eclipse that had the right look. 
All I really wanted to find out is if the date could change and still show 
correct eclipses, so I think this proves that much.

Hey John, thanks a whole lot for sharing your pov file!

-- 
Bob H  www.3digitaleyes.com
http://3digitaleyes.com/imagery/

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Ack!  Neglected to mention I changed the OBS (observer) to be SUN instead of 
SHADOW, or else there wouldn't be anything to see.

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Thanks, Bob, I'm glad you found it useful.

I'd be careful about changing the size of the sun, moon and earth, but
changing the position of the camera can't do any harm.

I looked at your picture ... if you chose SUN as the viewpoint then (during
the eclipse) the moon should be in front of the earth.

I think I wrote somewhere in the code that a light source can't see the
shadows it makes.

I haven't tried running the code through POVRay in a while. I used rev 3.5
Does it still work with the latest revision?

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"pavium" <jrc### [at] tpgcomau> wrote in message 
news:web.44165789181997a38398f4b40@news.povray.org...
>
> I'd be careful about changing the size of the sun, moon and earth

I'm guessing you never meant for this to be about lunar eclipses, only solar 
eclipses.

> I looked at your picture ... if you chose SUN as the viewpoint then 
> (during
> the eclipse) the moon should be in front of the earth.

 Hmmm, well, it wasn't.  :)

> I think I wrote somewhere in the code that a light source can't see the
> shadows it makes.

Since I've raised the camera up out of the ecliptic it would have to see the 
shadow cast onto the moon from the earth... but if you meant shadowless, 
yeah the looks_like Sun object precludes any self-made shadows. And if that 
isn't what you're saying then I'm lost.

> I haven't tried running the code through POVRay in a while. I used rev 3.5
> Does it still work with the latest revision?

At first I thought it looked okay in 3.6.1b using the original date and time 
you had for the 1999 eclipse, but it seems like the second sun and moon you 
put in there don't belong. I can't really say what is happening, I jumped 
into changing things before I bothered to check on it. The area_light I 
added for the sunlight really changes the shadow a lot, too. I have that at 
the SUNRAD (radius) at the moment and it looks good, along with the moon 
being scale 1 not 2.

Something especially confusing me is how the day and night sides of the 
earth don't seem to correspond to the sun (when I changed to this upcoming 
lunar eclipse), which is rather strange considering the earth's shadow still 
shows up on the moon as expected. I'm sure I'd keep discovering new things 
if I kept reading through the script. The math itself I dare not touch!

Bob

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This is a perfect example of how it helps to read a file thoroughly. I 
wasn't paying any attention to most of it as I went in and began changing 
things just so I could get a POV-rendered look at that lunar penumbral 
eclipse before tonight. I didn't even try the commented out line for look_at 
<XMOON,YMOON,ZMOON> until a little while ago! Of course, I wanted the Earth 
in the view anyway, so... I've probably made a real mess of your original 
file, which I'm keeping separate.  ;)

I think maybe I know now what you were saying about the light and shadow, 
how the camera viewpoint is found along the moon and sun line then placed 
near the earth on the sunlit side. At least I guess I do, this kind of thing 
makes my head spin. The part immediately after the Earth and Moon object 
creation is the calculations for that. Not sure if the comments have an 
error where it says: x^2 + y2 + z^2 = EARTHRAD^2^ since I'd have thought it 
would say x^2 + y^2 + z^2 = EARTHRAD^2 but I'm not the one to second guess 
you on that. Ha ha!

Fun to mess around with it, regardless of my ineptitude.

Bob

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Well I only tried to model a lunar eclipse once so I could get the image on
the 'home' page. It wasn't ideal, but it gave the impression of the Moon in
shadow so I used it.

Eclipse.pov models the Sun, Earth and Moon at any given time and date.

Solar Eclipses seem more interesting because you can recognise the places
the Moon's shadow falls on, but recreating the circumstances of a lunar
eclipse should be just a matter of finding the date and time when it
happens (what astronomers call the central eclipse, I think) and then
pointing the camera at the Moon's co-ordinates instead of the Earth's. The
Earth's shadow is much bigger than the Moon and you might see only a
completely darkened Moon. On the other hand a penumbral eclipse might not be
the spectacle you'd like it to be.

My comment about the light source not being able to see the shadows it makes
follows from the idea that a shadow is a place where a light source can't
reach. If your eye was a light source, it couldn't see the shadows it makes
because they're in places where your eye (as light source) isn't visible.

In a way, it reminds me of the signs we see on trucks here in Australia - If
you can't see my mirrors, I can't see you.

And I'm talking in general terms about a simple system with one real light
source and not about POVRay constructs like shadowless light sources.

It's very strange if the night and day sides of the Earth don't correspond
to the Sun because eclipse.pov (in spite of the complexity of the
astronomical calculations) essentially creates a scene with a light source
and two bodies. If POVRay can't render a simple scene like that, there's
something seriously wrong ;-)

The only fiction I introduced to my simple scene was the additional Sun and
Moon so that I could get a distinct umbra and penumbra. These extra
components are arranged inline with the real Sun and Moon so the shadows
they create line up too.

An area light sounds like a more realistic approach, provided it's
dimensioned properly, but the edges of the Moon's shadow will be indistinct
and
you won't be able to see the path of totality. I once found on the Internet
a short movie of a solar eclipse taken by Shuttle astronauts. The shadow
was precisely as I've just described.

It looks like I'll have to invest in some hardware which will run POVRay
once more. I have actually tried running POVRay on a 75MHz Pentium under
OpenBSD with no graphics capability. It actually generated 25x80 ASCII text
images onscreen while saving GIF files to disk. It was fascinating to watch
but only marginally faster than watching grass grow.

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