Are stored photon maps resolution independant? i.e. if I save a photon map while
rendering at 320*240, can I load the map and get the correct result when
rendering at 800*600?

--
#macro A(V,B,C,R)#while(B-256)#if(V-128/B>=0)sphere{0,.5translate<C-4R-1,9>
pigment{rgb<1-C/8R/2C/8>}}#local V=V-128/B;#end#local B=B*2;#local C=C+1;#
end#end A(234,1,0,2)A(85,1,0,1)A(81,1,0,0)light_source{-5 1}//Tom Melly

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On Fri, 20 Sep 2002 12:06:19 -0400, Tom Melly quoth:

> Are stored photon maps resolution independant? i.e. if I save a photon
> map while rendering at 320*240, can I load the map and get the correct
> result when rendering at 800*600?

This has come up before, in povray.advanced-users, under the topic of
"Saving Data" on June 26, 2002.  The reply:

Mark Wagner wrote:
>Rafal 'Raf256' Maj wrote in message ...
>>Hi,
>>when data for photons and/or media can NOT be safle loaded ? I ques that
>>camera moving/rotation is alwys safe, and any other changes is scene
>>(objects or lights) is not safe - is this correct ?
>
>Moving the camera is always safe.  Moving lights that do not cast photons
>is always safe.  Moving objects that do not have photons shot at them,
>that do not recieve photons, and would not recieve photons in the new
>location is always safe.  Moving an object that recieves photons to a new
>location where it does not recieve photons is sometimes safe.  Moving an
>object to a location where it recieves photons, moving an object that has
>photons shot at it, or moving a light that casts photons is not safe.
>
>Changing the texture of an object that recieves photons is safe. 
>Changing the texture of an object that has photons shot at it produces
>results that are not realistic, but can be useful sometimes.

So, in other words, yes.
 

-- 
Mark

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Mark Wagner <mar### [at] gtenet> wrote in 
news:pan### [at] gtenet

>>>Hi,
>>>when data for photons and/or media can NOT be safle loaded ? I ques that
>>>camera moving/rotation is alwys safe, and any other changes is scene
>>>(objects or lights) is not safe - is this correct ?
>>Moving the camera is always safe.  Moving lights that do not cast photons

This is NOT true for radiosity - camera can NOT see any surfaces that where 
hidden during saving radiosity. For this surfaces there is no radiosity 
data. Or - yes, the data can be loaded, but more radiosity data must be 
gathered (due to presense of new surfaces)


-- 
#macro g(U,V)(.4*abs(sin(9*sqrt(pow(x-U,2)+pow(y-V,2))))*pow(1-min(1,(sqrt(
pow(x-U,2)+pow(y-V,2))*.3)),2)+.9)#end#macro p(c)#if(c>1)#local l=mod(c,100
);g(2*div(l,10)-8,2*mod(l,10)-8)*p(div(c,100))#else 1#end#end light_source{
y 2}sphere{z*20 9pigment{function{p(26252423)*p(36455644)*p(66656463)}}}//M

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On Sat, 21 Sep 2002 06:00:59 -0400, Rafal 'Raf256' Maj quoth:

> Mark Wagner <mar### [at] gtenet> wrote in
> news:pan### [at] gtenet
> 
>>>>Hi,
>>>>when data for photons and/or media can NOT be safle loaded ? I ques
>>>>that camera moving/rotation is alwys safe, and any other changes is
>>>>scene (objects or lights) is not safe - is this correct ?
>>>Moving the camera is always safe.  Moving lights that do not cast
>>>photons
> 
> This is NOT true for radiosity - camera can NOT see any surfaces that
> where hidden during saving radiosity. For this surfaces there is no
> radiosity data. Or - yes, the data can be loaded, but more radiosity
> data must be gathered (due to presense of new surfaces)

The original question was dealing with photons, for which it IS true.

-- 
Mark

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"Mark Wagner" <mar### [at] gtenet> wrote in message
news:pan### [at] gtenet...
> On Fri, 20 Sep 2002 12:06:19 -0400, Tom Melly quoth:
>

<snip>

Thanks Mark - how about:

1) changing image resolution
2) changing media density (if using media photons)

Also, I was surprised to read that changing the camera position was okay. This
implies that photons are mapped to objects rather than positions. Is there an
idiot's explanation as to how photons work in Pov?

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In article <3d8edcda$1@news.povray.org>,
 "Tom Melly" <tom### [at] tomandlucouk> wrote:

> Also, I was surprised to read that changing the camera position was okay. This
> implies that photons are mapped to objects rather than positions. Is there an
> idiot's explanation as to how photons work in Pov?

It just means that the camera position doesn't matter. Why should it? 
The camera doesn't emit photons and doesn't interact with them. As for 
position vs. object: a photon at < 1, 2, 3> is a photon at < 1, 2, 3> no 
matter where the camera is. POV might keep track of which photons hit 
which surfaces (I don't know, I haven't looked at the source), but that 
has no effect on whether or not you can move the camera.

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/

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"Christopher James Huff" <chr### [at] maccom> wrote in message
news:chr### [at] netplexaussieorg...

> The camera doesn't emit photons and doesn't interact with them. As for
> position vs. object: a photon at < 1, 2, 3> is a photon at < 1, 2, 3> no

Oops, dunno what I was thinking of (well, I do, but it still doesn't make any
sense).

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On Mon, 23 Sep 2002 05:20:26 -0400, Tom Melly quoth:

> "Mark Wagner" <mar### [at] gtenet> wrote in message
> news:pan### [at] gtenet...
>> On Fri, 20 Sep 2002 12:06:19 -0400, Tom Melly quoth:
>>
>>
> <snip>
> 
> Thanks Mark - how about:
> 
> 1) changing image resolution
> 2) changing media density (if using media photons)
> 
> Also, I was surprised to read that changing the camera position was
> okay. This implies that photons are mapped to objects rather than
> positions. Is there an idiot's explanation as to how photons work in
> Pov?

Photons are mapped to positions, not objects.  The reason you can move
the camera around safely is because, unlike with radiosity, POV
calculates *all* photons in the scene, not just those that would be
visible from the current position.

Idiot's Guide:

When you specify that an object is to have photons shot at it, POV traces
rays at that object from each light source that casts photons.  It then
reflects and refracts each ray as it would during regular ray-tracing.
Whenever one of those rays hits an object, POV-Ray stores some data about
that ray-object intersection: where it took place, and what color the ray
was at that point.  This is a photon.

When you specify that an object is to have photons shot at it, POV-Ray
treats that object's texture as being opaque for the purpose of shadow
testing.  Additionally, if you've got any photons in the scene, then
whenever POV does lighting calculations for a point, it does an additional
check to see if any photons have been stored nearby.  The number of
photons it looks for, and how far it goes to find them, are set by your
photon settings.  In effect, it combines all the photons it has found for
the point and treats them as an additional light source illuminating that
point.

More advanced topics such as media photons I haven't figured out entirely
yet.

-- 
Mark

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"Mark Wagner" <mar### [at] gtenet> wrote in message
news:pan### [at] gtenet...

<snip>

Ta very much...

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