I'm trying to create the Sun in my scene. However I am having trouble 
getting it to be the rights size. Here is what I'm doing:

#include "sunpos.inc"
#declare Meters			= 60;		// 60 units = 1 meter.
#declare SunRadius		= 695700000 * Meters;
#declare SunDistance		= 1.4960e11 * Meters;
#declare Source_Distance	= 100000 * Meters;
#declare Source_Location	= SunPos(2016, 9, 6, 11, 0, 0, 39.7684, 0);
#declare Source_Location	= 
vnormalize(<+Source_Location.x,-Source_Location.y,+Source_Location.z>) * 
Source_Distance;

// Either this or the next line
//#declare Source_Radius		= Source_Distance/SunDistance * SunRadius;
// This is the next line
#declare Source_Radius		= tand(4/15) * Source_Distance;

As you can see I tried two methods. They produce similar results as far 
as I can tell. But to me the Sun still seems too small.

Look at the scene here:

http://isometricland.net/panorama/pannellum.htm?config=pano_lego_carriagehouse.json

What am I doing wrong? Are my eyes wrong?

Thanks.

Mike

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Le 08/09/2016 à 03:54, Mike Horvath a écrit :
> I'm trying to create the Sun in my scene. However I am having trouble
> getting it to be the rights size. Here is what I'm doing:
>
> #include "sunpos.inc"
> #declare Meters            = 60;        // 60 units = 1 meter.
> #declare SunRadius        = 695700000 * Meters;
> #declare SunDistance        = 1.4960e11 * Meters;
> #declare Source_Distance    = 100000 * Meters;
> #declare Source_Location    = SunPos(2016, 9, 6, 11, 0, 0, 39.7684, 0);
> #declare Source_Location    =
> vnormalize(<+Source_Location.x,-Source_Location.y,+Source_Location.z>) *
> Source_Distance;
>
> // Either this or the next line
> //#declare Source_Radius        = Source_Distance/SunDistance * SunRadius;
> // This is the next line
> #declare Source_Radius        = tand(4/15) * Source_Distance;
>
> As you can see I tried two methods. They produce similar results as far
> as I can tell. But to me the Sun still seems too small.
>
> Look at the scene here:
>
> http://isometricland.net/panorama/pannellum.htm?config=pano_lego_carriagehouse.json
>
>
> What am I doing wrong? Are my eyes wrong?
>

The data might not be what they stand for.
The sun should appears to be about 32 minutes of arc, that's nearly half 
a degree.
So your tand(4/15) is kind of correct ( 8/15 for the diameter )

That would be correct within a scene with a viewing angle of 10° : big 
sun when you focus on something, with enough clouds to allow you to star 
at the sun.

With a naked sky, you cannot star at the sun (you should not, or you 
will be blind soon), and you might think it is bigger. But you do not 
see it really.

Back to your question: it is all in the brain, and you get badly 
influenced by pictures and movies which zoomed the sun and the moon for 
dramatic effects.

Half a degree, it's all of its apparent diameter; But it's 10% of a 5° 
focus!

Binoculars which do x16 would display 3.5° as 56°
(notation of binoculars are G x D, G is the multiplier of the angle, and 
D the diameter of the input lens)

Post a reply to this message

On 9/8/2016 2:16 AM, Le_Forgeron wrote:
> Le 08/09/2016 à 03:54, Mike Horvath a écrit :
>> I'm trying to create the Sun in my scene. However I am having trouble
>> getting it to be the rights size. Here is what I'm doing:
>>
>> #include "sunpos.inc"
>> #declare Meters            = 60;        // 60 units = 1 meter.
>> #declare SunRadius        = 695700000 * Meters;
>> #declare SunDistance        = 1.4960e11 * Meters;
>> #declare Source_Distance    = 100000 * Meters;
>> #declare Source_Location    = SunPos(2016, 9, 6, 11, 0, 0, 39.7684, 0);
>> #declare Source_Location    =
>> vnormalize(<+Source_Location.x,-Source_Location.y,+Source_Location.z>) *
>> Source_Distance;
>>
>> // Either this or the next line
>> //#declare Source_Radius        = Source_Distance/SunDistance *
>> SunRadius;
>> // This is the next line
>> #declare Source_Radius        = tand(4/15) * Source_Distance;
>>
>> As you can see I tried two methods. They produce similar results as far
>> as I can tell. But to me the Sun still seems too small.
>>
>> Look at the scene here:
>>
>> http://isometricland.net/panorama/pannellum.htm?config=pano_lego_carriagehouse.json
>>
>>
>>
>> What am I doing wrong? Are my eyes wrong?
>>
>
> The data might not be what they stand for.
> The sun should appears to be about 32 minutes of arc, that's nearly half
> a degree.
> So your tand(4/15) is kind of correct ( 8/15 for the diameter )
>
> That would be correct within a scene with a viewing angle of 10° : big
> sun when you focus on something, with enough clouds to allow you to star
> at the sun.
>
> With a naked sky, you cannot star at the sun (you should not, or you
> will be blind soon), and you might think it is bigger. But you do not
> see it really.
>
> Back to your question: it is all in the brain, and you get badly
> influenced by pictures and movies which zoomed the sun and the moon for
> dramatic effects.
>
> Half a degree, it's all of its apparent diameter; But it's 10% of a 5°
> focus!
>
> Binoculars which do x16 would display 3.5° as 56°
> (notation of binoculars are G x D, G is the multiplier of the angle, and
> D the diameter of the input lens)
>

Thanks! I found this thread that discusses the same sort of things:

http://news.povray.org/povray.binaries.images/thread/%3C51b18d7d%40news.povray.org%3E/


Mike

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> Thanks! I found this thread that discusses the same sort of things:
>
>
http://news.povray.org/povray.binaries.images/thread/%3C51b18d7d%40news.povray.org%3E/

Yes I remember that very discussion :-)

Something I worked out since then, is that a large part of the problem 
is the mismatch between the field-of-view of your image, and the FOV of 
the physical device you are viewing it on.

On my desktop monitor I get an hFOV of about 35 degrees, I suspect if 
you render an image showing the sun with an hFOV to match, it will look 
a more realistic size.

Note that in certain 3D games (especially car racing simulators) it is 
very important to get the virtual FOV to match your real life display, 
otherwise it messes up all your judgement of depth and perspective, the 
problem with the sun size "looking wrong" is just an extreme example of 
this.

Post a reply to this message

On 9/8/2016 2:54 AM, scott wrote:
>> Thanks! I found this thread that discusses the same sort of things:
>>
>>
http://news.povray.org/povray.binaries.images/thread/%3C51b18d7d%40news.povray.org%3E/
>>
>
> Yes I remember that very discussion :-)
>
> Something I worked out since then, is that a large part of the problem
> is the mismatch between the field-of-view of your image, and the FOV of
> the physical device you are viewing it on.
>
> On my desktop monitor I get an hFOV of about 35 degrees, I suspect if
> you render an image showing the sun with an hFOV to match, it will look
> a more realistic size.
>
> Note that in certain 3D games (especially car racing simulators) it is
> very important to get the virtual FOV to match your real life display,
> otherwise it messes up all your judgement of depth and perspective, the
> problem with the sun size "looking wrong" is just an extreme example of
> this.
>

For the actual renders I'm stuck at 90 degrees for the camera angles. 
It's the Web app that needs to be set to the correct FOV.

Mike

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