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28 Mar 2024 08:50:28 EDT (-0400)
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From: Stephen
Subject: Re: Ringworld (continued)
Date: 7 Aug 2018 07:09:07
Message: <5b697dd3$1@news.povray.org>
On 07/08/2018 11:51, clipka wrote:
> Am 07.08.2018 um 12:33 schrieb Stephen:
> 
>> A close up of the terminator on the Ringworld.
>> The area light does make a difference.
>> Using
>>   light_source {  // Light_Source2
>>    < 0.000000, 0.000000, 0.000000 >, colour rgb <1.000,1.000,1.000>*1.500
>>    area_light <3.400000,0.000000,0.000000>, <0.000000,3.400000,0.000000>,
>> 23, 23
>>
>>    circular
>>    orient
>>    adaptive 5
> 
> And it better does. You don't want the light to blink off
> instantaneously - you do want some twilight time.
> 

That is the whole idea, I believe. ;)

As for maths the area_light axis vectors should be doubled to 6.8 not 3.4
I was thinking radius as opposed to diameter.


-- 

Regards
     Stephen


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From: Stephen
Subject: Re: Ringworld (continued)
Date: 7 Aug 2018 07:23:24
Message: <5b69812c$1@news.povray.org>
On 07/08/2018 12:07, Thomas de Groot wrote:
> On 7-8-2018 12:51, clipka wrote:
>> Am 07.08.2018 um 12:33 schrieb Stephen:
>>
>>> A close up of the terminator on the Ringworld.
>>> The area light does make a difference.
>>> Using
>>>   light_source {  // Light_Source2
>>>    < 0.000000, 0.000000, 0.000000 >, colour rgb 
>>> <1.000,1.000,1.000>*1.500
>>>    area_light <3.400000,0.000000,0.000000>, 
>>> <0.000000,3.400000,0.000000>,
>>> 23, 23
>>>
>>>    circular
>>>    orient
>>>    adaptive 5
>>
>> And it better does. You don't want the light to blink off
>> instantaneously - you do want some twilight time.
>>
> 
> I agree. What I meant earlier was that, with the camera at /planetary/ 
> distances from the ring, the penumbra would hardly be visible. Up close, 
> and more so on the ring surface, of course the penumbra matters. 
> However, if the area_light is set while the camera is at a /planetary/ 
> distance, it will most probably be grossly exaggerated because otherwise 
> you would not be able to see it properly in a render.
> 

Do you mean that the penumbra would need to be exaggerated so it can be 
seen?
I thought that too but when I created two big sticks located at opposite 
sides of the star and clipping the same edge of a shadow square. The 
divergence at the ring was quite large.
I might try moving the shadow square radius back to the quoted radius 
and adjust the length of the shadow square to get equal day/night.
This image was taken from slightly beyond the other side of the ring and 
above a bit.


-- 

Regards
     Stephen


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From: Stephen
Subject: Re: Ringworld (continued)
Date: 7 Aug 2018 08:01:39
Message: <5b698a23$1@news.povray.org>
On 07/08/2018 12:23, Stephen wrote:
> I might try moving the shadow square radius back to the quoted radius 
> and adjust the length of the shadow square to get equal day/night.

As threatened. :-)

Twilight is less obvious.

-- 

Regards
     Stephen


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From: Alain
Subject: Re: Ringworld (continued)
Date: 7 Aug 2018 10:31:57
Message: <5b69ad5d@news.povray.org>
Le 18-08-07 à 06:33, Stephen a écrit :
> On 07/08/2018 11:29, Stephen wrote:
>> No, don't follow my maths.
>>
>> Using the data from this site. I did a quick model.
>> http://www.alcyone.com/max/reference/scifi/ringworld.html
>> I adjusted the Shadow square ring radius until the day/night cycle 
>> looked equal.(multiplied the radius by 0.587587699)
> 
> A close up of the terminator on the Ringworld.
> The area light does make a difference.
> Using
>   light_source {  // Light_Source2
>    < 0.000000, 0.000000, 0.000000 >, colour rgb <1.000,1.000,1.000>*1.500
>    area_light <3.400000,0.000000,0.000000>, 
> <0.000000,3.400000,0.000000>, 23, 23
> 
>    circular
>    orient
>    adaptive 5
> 

The 23, 23  get bumped up to 33, 33

adaptive 5 mean start at subdivision 5, or start with 33, 33 samples. 
This effectively disable the adaptive optimization.
In the present case, adaptive 0 is good.

adaptive 0 start at 2 by 2
adaptive 1 start at 3 by 3
adaptive 2 start at 5 by 5
adaptive 3 start at 9 by 9
adaptive 4 start at 17 by 17
adaptive 5 start at 33 by 33
adaptive 6 start at 65 by 65
...

You need a number of samples at least 2 step up to get some appreciable 
benefit. For adaptive 0, use at least 5 by 5, and 9 by 9 or more in most 
cases.
For adaptive 1, better to start around 17 by 17.
For adaptive 5, you start to see an improvement around 129 by 129...


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From: Stephen
Subject: Re: Ringworld (continued)
Date: 7 Aug 2018 11:20:32
Message: <5b69b8c0@news.povray.org>
On 07/08/2018 15:33, Alain wrote:
> Le 18-08-07 à 06:33, Stephen a écrit :

>>
>> A close up of the terminator on the Ringworld.
>> The area light does make a difference.
>> Using
>>   light_source {  // Light_Source2
>>    < 0.000000, 0.000000, 0.000000 >, colour rgb <1.000,1.000,1.000>*1.500
>>    area_light <3.400000,0.000000,0.000000>, 
>> <0.000000,3.400000,0.000000>, 23, 23
>>
>>    circular
>>    orient
>>    adaptive 5
>>
> 
> The 23, 23  get bumped up to 33, 33
> 
> adaptive 5 mean start at subdivision 5, or start with 33, 33 samples. 
> This effectively disable the adaptive optimization.
> In the present case, adaptive 0 is good.
> 
> adaptive 0 start at 2 by 2
> adaptive 1 start at 3 by 3
> adaptive 2 start at 5 by 5
> adaptive 3 start at 9 by 9
> adaptive 4 start at 17 by 17
> adaptive 5 start at 33 by 33
> adaptive 6 start at 65 by 65
> ....
> 
> You need a number of samples at least 2 step up to get some appreciable 
> benefit. For adaptive 0, use at least 5 by 5, and 9 by 9 or more in most 
> cases.
> For adaptive 1, better to start around 17 by 17.
> For adaptive 5, you start to see an improvement around 129 by 129...

Thanks Alain, I seldom use area lights and this is the first time I have 
used adaptive.
When you said samples is that what the offline help names Size_1 & 
Size_2, in the line;
AXIS_1_VECTOR, AXIS_2_VECTOR, Size_1, Size_2?

-- 

Regards
     Stephen


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From: Mike Horvath
Subject: Re: Ringworld (continued)
Date: 7 Aug 2018 15:22:10
Message: <5b69f162$1@news.povray.org>
On 8/7/2018 4:20 AM, Stephen wrote:
>> That, or scale down the area_light's effective surface. At this 
>> planetary scale the area effect would be hardly noticeable imo.
>>
> 
> A point light gives the same result.
> 

I tried a point light, and the day/night cycles were equal. But Niven 
did specify the size of the star, and I checked my other numbers against 
his and they match.


Mike


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From: Mike Horvath
Subject: Re: Ringworld (continued)
Date: 7 Aug 2018 15:28:48
Message: <5b69f2f0$1@news.povray.org>
On 8/7/2018 7:09 AM, Stephen wrote:
> That is the whole idea, I believe. ;)
> 
> As for maths the area_light axis vectors should be doubled to 6.8 not 3.4
> I was thinking radius as opposed to diameter.
> 
> 

You just reminded me that I used the sun radius instead of diameter for 
the area light axes.

When instead using the diameter, I get some fuzziness but no real "night".

Sorry, Niven. Your math is bad.

Mike


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From: Stephen
Subject: Re: Ringworld (continued)
Date: 7 Aug 2018 17:52:59
Message: <5b6a14bb$1@news.povray.org>
On 07/08/2018 20:28, Mike Horvath wrote:
> On 8/7/2018 7:09 AM, Stephen wrote:
>> That is the whole idea, I believe. ;)
>>
>> As for maths the area_light axis vectors should be doubled to 6.8 not 3.4
>> I was thinking radius as opposed to diameter.
>>
>>
> 
> You just reminded me that I used the sun radius instead of diameter for 
> the area light axes.
> 

I now feel better. ;)


> When instead using the diameter, I get some fuzziness but no real "night".
> 

You don't have an "ambient" in there? (Before Clipka says anything. ;) )
> Sorry, Niven. Your math is bad.

Funnily enough, I did not notice that when I read the books. ;)
It is PovRay's fault. It is too realistic. :)

I think it is better to bring the shadow shields nearer the sun, for the 
data I found.

This last image (I promise) using Alain's settings, has a stary 
background to show that the night part of the ring is occluding the stars.

BTW Thanks for starting the thread. It has been a distraction for me 
when I don't feel up to starting a new project.


-- 

Regards
     Stephen


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Attachments:
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From: Mike Horvath
Subject: Re: Ringworld (continued)
Date: 7 Aug 2018 18:39:51
Message: <5b6a1fb7$1@news.povray.org>
On 8/7/2018 5:52 PM, Stephen wrote:
> Funnily enough, I did not notice that when I read the books. ;)
> It is PovRay's fault. It is too realistic. :)
> 
> I think it is better to bring the shadow shields nearer the sun, for the 
> data I found.
> 
> This last image (I promise) using Alain's settings, has a stary 
> background to show that the night part of the ring is occluding the stars.
> 
> BTW Thanks for starting the thread. It has been a distraction for me 
> when I don't feel up to starting a new project.
> 
> 

Hold on. I just noticed I wasn't using the correct sizes for the shadow 
squares. And I had 40 of them instead of 20. I will need to redo them.


Mike


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From: Thomas de Groot
Subject: Re: Ringworld (continued)
Date: 8 Aug 2018 02:22:44
Message: <5b6a8c34$1@news.povray.org>
On 7-8-2018 14:01, Stephen wrote:
> On 07/08/2018 12:23, Stephen wrote:
>> I might try moving the shadow square radius back to the quoted radius 
>> and adjust the length of the shadow square to get equal day/night.
> 
> As threatened. :-)
> 
> Twilight is less obvious.
> 

Yes, but I think it is looking natural from that distance. On the ring, 
twilight would be gradual, as expected.

-- 
Thomas


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