Hi all,

This has probably been asked before, but how large a real world
environment can can be simulated in POV.

I want to do a planetary system, showing, as near as possible, real
scale distances and body sizes.

eg. maybe 0.1 POV unit = 1 kilometer.

I know there can be work arounds using forced perspective, which I have
used before, but I want to try something different.

Thanks Alex.
-- 
  ,-._|\  Alex McMurray
 /  Oz  \ ale### [at] melbpcorgau               Melbourne PC User Group.
 \_,--.x/ Melton. Vic.  3337                     Australia
       v

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> I want to do a planetary system, showing, as near as possible, real
> scale distances and body sizes.
>
> eg. maybe 0.1 POV unit = 1 kilometer.
>
> I know there can be work arounds using forced perspective, which I have
> used before, but I want to try something different.

POV-Ray should be able to handle it. If distances start getting too big,
just decrease your scale.

You should know, though, that if you place things at the correct positions
and size, they'll be so small and far apart from each other that if you can
see one of them, you can't see any of the others, except for the sun. Just
think about how small jupiter and saturn and other planets look from earth.

- Slime
[ http://www.slimeland.com/ ]
[ http://www.slimeland.com/images/ ]

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As Povray uses floatingpoint algorithms, it shouldn't your problem, to choose
the right scale ...

The problems will arise, if you have different sized objects, that hafe sizes
in different orders ...

That means:
It is perfectly OK, to compute everything with 10^5 units...
Say you have one planet, size 5000, distance 10000000, and another planet,
size 5500, distance= planet1+500 ...

should make no big problems ...

/BUT:/
If you choose to create structures on planet2, that have the size of 0.1
units, you will get accuracyproblems as in floatingpoint aritmethics they
will probably cancel out with the distance of which is a number, 10^8 times
higher. This alone maybe won't make the problem, but often there are
calculations, that involve solving of high-order equations(x^2 , x^4 or even
x^6 ...). Then the power wil raise to the double (10^16), or even more, and
then even a double-float-number is no longer able to hold these values ...

... of course, it can stre numbers like, maybe, 10^54 or 10^55... but in
these regions there is no longer any difference between 10^54+1 or 10^54+2
... they will be the same...


So your problem shouldn't be how many POV-Units is one kilometer, but
instead: What is the largest number you will use, and what is the highest
accuracy, you need...

hence, it should be perfectly possible, to scale a complete scene by a
factor, maybe 10^20, to make it bigger, or by 10^-20 to make it smaller ...

As long as the complete scene gets scaled (including cameras ligths and
everything) there shouln't any big difference ...


I hope this hole story makes sense to you...
Maybe someone else can explain better ...


--
Jan Walzer <jan### [at] lzernet>

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<snip> 
You should know, though, that if you place things at the correct
positions
> and size, they'll be so small and far apart from each other that if you can
> see one of them, you can't see any of the others, except for the sun. Just
> think about how small jupiter and saturn and other planets look from earth.
> 
> - Slime
> [ http://www.slimeland.com/ ]
> [ http://www.slimeland.com/images/ ]

If the planets are aligned, and the camera angle is small you should be
able to get a bunch of planets in one picture.  

-- 
Dan Johnson 

http://www.geocities.com/zapob

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Alex McMurray wrote:

> >I want to do a planetary system, showing, as near as possible, real
> >scale distances and body sizes.

It seems like this would work, but for some reason it doesn't. If you make
a sphere with a radius of 400,000 units with an ambient value as high as
you like, and place yourself 93 million units from it, you will not be able
to see it, as you would the sun from the earth. I don't know if it is an
internal math thing in POV-Ray or what, but I know that it is ture. Try it.

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> It seems like this would work, but for some reason it doesn't. If you make
> a sphere with a radius of 400,000 units with an ambient value as high as
> you like, and place yourself 93 million units from it, you will not be
able
> to see it, as you would the sun from the earth. I don't know if it is an
> internal math thing in POV-Ray or what, but I know that it is ture. Try
it.
>
>
>
I've had problems with this before, it's just a matter of scaling, use a
larger base scale

Try this example which uses the sun, moon and earth at their proportional
sizes and scaled using 'scl'
with scl=1, the sun isn't visible, but with scl=1000 it is

-tgq


//start

global_settings{
  ambient_light 1
  assumed_gamma 1.0
  max_trace_level 100
}

#default{finish{ambient 0 diffuse 0.75}}

#declare Scl =1000
#declare ERad=6378.14/Scl
#declare SRad=695000/Scl
#declare SDis=149600000/Scl
#declare MRad=1737.4/Scl
#declare MDis=384400/Scl


//#declare lo = <-100,50,-200>;
//#declare la = <0,15,0>;

#declare lo = <0,ERad+1/1000/Scl,-SDis>;
#declare la = <0,0,0>;

camera {
  up y
  right x*image_width/image_height
  angle 25
  location lo
  look_at  la
}

//
// *******  L I G H T S  *******
//

#declare LB=sphere{0 SRad pigment{rgb <1,1,0>} finish{ambient 100}}

light_source {0
  rgb <1,1,1>
  looks_like{LB}
}
light_source {0
  rgb <1,1,1>
  translate <0,0,-SDis>
}

#declare E1=material{texture{pigment{rgb<0,0,1>}}}
#declare M1=material{texture{pigment{rgb<1,1,1>}}}
#declare CM=material{texture{pigment{rgb 0}}}

sphere{<0,0,-SDis> ERad material{E1} no_shadow}
sphere{<0,0,MDis> MRad material{M1} rotate -x*2 translate <0,0,-SDis>}
//end

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> If the planets are aligned, and the camera angle is small you should be
> able to get a bunch of planets in one picture.

bunch of dots you mean


--

Rick

Kitty5 WebDesign - http://Kitty5.com
POV-Ray News & Resources - http://Povray.co.uk
TEL : +44 (01270) 501101 - FAX : +44 (01270) 251105 - ICQ : 15776037

PGP Public Key
http://pgpkeys.mit.edu:11371/pks/lookup?op=get&search=0x231E1CEA

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You could get some planets larger than 1 pixel if the camera angle is
**VERY** small and the camera is **VERY** far away.  In other words, the
distances between the planets are negligible compared to the distance of
the camera.


Rick [Kitty5] <ric### [at] kitty5com> wrote in message
news:3c0c05de@news.povray.org...
> > If the planets are aligned, and the camera angle is small you should
be
> > able to get a bunch of planets in one picture.
>
> bunch of dots you mean
>
>
> --
>
> Rick
>
> Kitty5 WebDesign - http://Kitty5.com
> POV-Ray News & Resources - http://Povray.co.uk
> TEL : +44 (01270) 501101 - FAX : +44 (01270) 251105 - ICQ : 15776037
>
> PGP Public Key
> http://pgpkeys.mit.edu:11371/pks/lookup?op=get&search=0x231E1CEA
>
>

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> It seems like this would work, but for some reason it doesn't. If you
make
> a sphere with a radius of 400,000 units with an ambient value as high
as
> you like, and place yourself 93 million units from it, you will not be
able
> to see it, as you would the sun from the earth. I don't know if it is
an
> internal math thing in POV-Ray or what, but I know that it is ture.
Try it.

Yes, setting radius=4 and distance=930 works.  Multiply by 10 and
repeat, and it works, all the way up to 40,000 and 9.3 million.  Then it
just disappears.

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Andrew wrote:

> > It seems like this would work, but for some reason it doesn't. If you
> make
> > a sphere with a radius of 400,000 units with an ambient value as high
> as
> > you like, and place yourself 93 million units from it, you will not be
> able
> > to see it, as you would the sun from the earth. I don't know if it is
> an
> > internal math thing in POV-Ray or what, but I know that it is ture.
> Try it.
>
> Yes, setting radius=4 and distance=930 works.  Multiply by 10 and
> repeat, and it works, all the way up to 40,000 and 9.3 million.  Then it
> just disappears.

Look at the relative size of the camera in your example scenarios.

In the first, the camera is huge in comparison to the objects (the camera is
planetary in size).

By the time you get to the last example, the scale of the camera in
relationship to the objects is now a very different matter.

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