I remember, not long ago, coming across a fantastic thread about true
sunlight. I recall it started out as a question about POV limitations
concerning the floating point accuracy ("Do I really have to make the sun 8
light minutes away?"), and quickly turned into a great discussion about how
far away the lightsource has to be to create parallel rays.

    I would really like to see it again (I foolishly failed to save it).
Anybody know?

    Thanks,

    -Eli

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Eli Ewok Brody <ewo### [at] yahoocom> wrote:
: how
: far away the lightsource has to be to create parallel rays.

  Sunlight rays are not parallel because the Sun is an area light.

  See:
http://www.students.tut.fi/~warp/povVFAQ/misconceptions.html#simulatingsun

-- 
#macro N(D,I)#if(I<6)cylinder{M()#local D[I]=div(D[I],104);M().5,2pigment{
rgb M()}}N(D,(D[I]>99?I:I+1))#end#end#macro M()<mod(D[I],13)-6,mod(div(D[I
],13),8)-3,10>#end blob{N(array[6]{11117333955,
7382340,3358,3900569407,970,4254934330},0)}//                     - Warp -

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I think that's what I remember seeing.
    It's obvious an area light - the sun disc isn't a point. The sun is so
far away, that the light it generates closely aproximates parallel rays,
though.
    But the atmosphere point was well taken. Even if it was parallel, the
atmosphere bends it in crazy ways.

    Thanks,
    -Eli

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Eli Ewok Brody <ewo### [at] yahoocom> wrote:
:     It's obvious an area light - the sun disc isn't a point. The sun is so
: far away, that the light it generates closely aproximates parallel rays,
: though.

  Light rays coming from a light source with a visible area are never
parallel, no matter how far it is.
  It's only when the light source is practically a point light when the
light rays start to be practically parallel. However, the Sun isn't.

-- 
#macro N(D,I)#if(I<6)cylinder{M()#local D[I]=div(D[I],104);M().5,2pigment{
rgb M()}}N(D,(D[I]>99?I:I+1))#end#end#macro M()<mod(D[I],13)-6,mod(div(D[I
],13),8)-3,10>#end blob{N(array[6]{11117333955,
7382340,3358,3900569407,970,4254934330},0)}//                     - Warp -

Post a reply to this message