In article <4003c4eb$1@news.povray.org> , "Hughes, B." 
<omn### [at] charternet> wrote:
>> camera {
>>     location <3, 0, 0.5>
>>     right <0, 2, 0> // make sure this is same aspect ratio as output
>>     up <0, 0, 1>
>>     direction  <-1, 0, 0>
>> }
>
>  camera {
>      location <3, 0, 0.5>
>      right image_width/image_height*y
>      up <0, 0, 1>
>      direction  <-1, 0, 0>
>  }

For a 640x320 image, the resulting camera you suggest will be absolutely
identical!  And it cannot solve the "problem" with the sphere either.

So what is the point of your suggestion? ;-)  Neither image_width nor
image_height are appropriate for this scene; nor do they belong in 99% of
the scenes where they are (ab)used.

The reason the sphere appears distorted is the default perspective camera.
So there is nothing wrong with the scene.  The perspective camera will make
objects that are close and not in the center of the image appear distorted,
which is especially visible if the image aspect ratio is on the extreme side
of things.  Depending on the scene, I would suggest to either use a smaller
camera angle (and increase the camera to object distance) or select another
camera (some trial and error may be necessary in that case).

    Thorsten

____________________________________________________
Thorsten Froehlich
e-mail: mac### [at] povrayorg

I am a member of the POV-Ray Team.
Visit POV-Ray on the web: http://mac.povray.org

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> My resulting image has some shearing so the spheres looks more
> like eggs.  I'm not sure what I'm doing wrong.

The output is correct. It looks weird because you don't usually see this
effect in real life; that's because you don't really focus on objects in
your peripheral vision like those spheres are.

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

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"Thorsten Froehlich" <tho### [at] trfde> wrote in message
news:4003d307$1@news.povray.org...
> >
> >  camera {
> >      location <3, 0, 0.5>
> >      right image_width/image_height*y
> >      up <0, 0, 1>
> >      direction  <-1, 0, 0>
> >  }
>
> For a 640x320 image, the resulting camera you suggest will be absolutely
> identical!  And it cannot solve the "problem" with the sphere either.

I replied too fast, perhaps. Some people say resolutions in the order of
height then width so I didn't pay much attention to that. I figured the
trouble was about something they had done to set resolution incorrectly for
the aspect ratio they were trying to get, so to me that meant I should
suggest dividing the width by height taken directly from whatever output
size was being used.

> So what is the point of your suggestion? ;-)  Neither image_width nor
> image_height are appropriate for this scene; nor do they belong in 99% of
> the scenes where they are (ab)used.

I abuse it often just so I don't have to worry about what resolutions I set.
:-)

> The reason the sphere appears distorted is the default perspective camera.

That thought occured to me and then I skipped mentioning it because of how
basic that phenomenon seems to me anymore. Bad decision. You're absolutely
correct about using narrower angles of view or a more suitable camera
projection type.

Bob H.

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It once again feels like maintaining the povQ&T pages is futile since
no-one uses it to answer questions already answered there.

http://tag.povray.org/povQandT/misconceptions.html#perspectivespheres

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

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Of course you get all the negative evidence, so here's a positive. I've
used the Q&T pages many times, and really appreciate them. I have
a terrible memory so I like to page through them on occasion to
remind myself of the possibilities.

I really like the way they're written, clear and easy to understand,
with an eye toward practicality.

I know this will go over like a lead balloon here, but I actually
appreciate the occasional RTFM question as it refreshes my memory
and sometimes spurs useful discussion. There are a lot of nice
resources out there but sometimes I can't remember where a
topic or question was discussed.


Warp wrote:
>  It once again feels like maintaining the povQ&T pages is futile since
>no-one uses it to answer questions already answered there.
>
>http://tag.povray.org/povQandT/misconceptions.html#perspectivespheres

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"Warp" <war### [at] tagpovrayorg> wrote in message news:400406b5@news.povray.org...
>   It once again feels like maintaining the povQ&T pages is futile since
> no-one uses it to answer questions already answered there.
>

As renderdog points out, your only evidence is, de facto, negative. That said,
to a certain extent you're probably right - humans being wot they are, we never
believe our problems aren't unique... (and hence cannot be in a faq).

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Thorsten,
I also like to use a camera with image_width / image_height for the right.
Then I can change aspect ratio at render time without changing the script
file. So anyway, why is it abuse? Are there drawbacks to this method
that some of us are not aware? Also, I always use a perspective camera
because typically I'm rendering stereo pairs, and it is difference in
perspective
that creates the stereo effect. Would orthographic cameras work too?
Guess I should experiment.

TIA
Harold

"Thorsten Froehlich" <tho### [at] trfde> wrote in message
news:4003d307$1@news.povray.org...
> In article <4003c4eb$1@news.povray.org> , "Hughes, B."
> <omn### [at] charternet> wrote:
> >
> >  camera {
> >      location <3, 0, 0.5>
> >      right image_width/image_height*y
> >      up <0, 0, 1>
> >      direction  <-1, 0, 0>
> >  }
>
> For a 640x320 image, the resulting camera you suggest will be absolutely
> identical!  And it cannot solve the "problem" with the sphere either.
>
> So what is the point of your suggestion? ;-)  Neither image_width nor
> image_height are appropriate for this scene; nor do they belong in 99% of
> the scenes where they are (ab)used.
>
> The reason the sphere appears distorted is the default perspective camera.
> So there is nothing wrong with the scene.  The perspective camera will
make
> objects that are close and not in the center of the image appear
distorted,
> which is especially visible if the image aspect ratio is on the extreme
side
> of things.  Depending on the scene, I would suggest to either use a
smaller
> camera angle (and increase the camera to object distance) or select
another
> camera (some trial and error may be necessary in that case).
>
>     Thorsten
>
> ____________________________________________________
> Thorsten Froehlich
> e-mail: mac### [at] povrayorg
>
> I am a member of the POV-Ray Team.
> Visit POV-Ray on the web: http://mac.povray.org

Post a reply to this message

Harold <bai### [at] 3dculturecom> wrote:
> I also like to use a camera with image_width / image_height for the right.
> Then I can change aspect ratio at render time without changing the script
> file.

  That's actually not really true.

  If you change the aspect ratio of the rendering resolution and the
camera adjusts automatically to that using "right image_width/image_height",
the image will be adjusted vertically so that part of the image from the
up and bottom sides will go out of the image (if changing to a wider
aspect ratio) or some extra scenery will appear at the top and the
bottom (if changing to a narrower aspect ratio).
  This might not always be the desired effect. You might want the extra
stuff to disappear/appear from the sides, not the top and the bottom,
or you might even want a combination of both (eg. when widening the
aspect ratio you want some stuff out from the top and bottom and
extra scenery appearing from the sides).
  Depending on what you want you will probably need to adjust the camera
parameters anyways.

> Are there drawbacks to this method that some of us are not aware?

  Some drawbacks are listed above.
  An additional drawback is that if you really want to keep the 4:3 aspect
ratio even though you are rendering with a resolution having a different
aspect ratio (eg. a 320x400 image for the Windows startup image), your
automatic camera setting will produce the undesired effect (ie. the aspect
ratio of the image is not kept to 4:3), thus you need to edit the camera
parameters again.

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

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>"Warp" <war### [at] tagpovrayorg> wrote
>   That's actually not really true.
>
Of course you are right in some respects, but it is
right because it does what I expect it to do and it is
what I want. The scene stays the same but the
aspect ratio changes. More on the sides or top is
the way I would want to change aspect ratio. A
panoramic aspect ratio does show a lot more of the
secene in the horizontal.



>   If you change the aspect ratio of the rendering resolution and the
> camera adjusts automatically to that using "right
image_width/image_height",
> the image will be adjusted vertically so that part of the image from the
> up and bottom sides will go out of the image (if changing to a wider
> aspect ratio) or some extra scenery will appear at the top and the
> bottom (if changing to a narrower aspect ratio).

Yeah, that is usually what I want. I wouldn't want the x or y dimensions
distorted.

>   An additional drawback is that if you really want to keep the 4:3 aspect
> ratio even though you are rendering with a resolution having a different
> aspect ratio (eg. a 320x400 image for the Windows startup image), your
> automatic camera setting will produce the undesired effect (ie. the aspect
> ratio of the image is not kept to 4:3), thus you need to edit the camera
> parameters again.

The few times I've made custom Windows start up images I have rendered
them in 4:3 aspect ratio then compressed them to half width in Paint Shop
Pro.
Guess one could do it directly with the camera statement. Probably better to
do it that way. Yet that is not what is meant by aspect ratio, at least not
as
it is used in film. It refers to simply the ratio of width to height of the
edges of
the image. The sort of compression represented by a 320x400 windows
startup image is analogous to "anamorphic" compression in the film industry,
which allows wide screen (wide aspect ratio) movies to be printed on
standard
35mm width film, then stretched by the projector lens to cover the wide
aspect
ratio.

HB

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Harold <bai### [at] 3dculturecom> wrote:
> >   If you change the aspect ratio of the rendering resolution and the
> > camera adjusts automatically to that using "right
> image_width/image_height",
> > the image will be adjusted vertically so that part of the image from the
> > up and bottom sides will go out of the image (if changing to a wider
> > aspect ratio) or some extra scenery will appear at the top and the
> > bottom (if changing to a narrower aspect ratio).

> Yeah, that is usually what I want. I wouldn't want the x or y dimensions
> distorted.

  That was not my point. Read it again.

> The few times I've made custom Windows start up images I have rendered
> them in 4:3 aspect ratio then compressed them to half width in Paint Shop
> Pro.

  The problem is that the 320x400 resolution does not have a 2:3 aspect ratio,
so half-width won't do it. (The aspect ratio is 4:5 to be exact.)

> Guess one could do it directly with the camera statement.

  No, you don't need to do anything abnormal with the camera statement.
Just define a default 4:3 camera (ie. you don't need to specify any
'right' vector) and render at 320x400 and you'll get an image which
looks ok when viewed with your monitor set to 320x400 resolution (as
it is when the Windows startup image is shown).


-- 
plane{-x+y,-1pigment{bozo color_map{[0rgb x][1rgb x+y]}turbulence 1}}
sphere{0,2pigment{rgbt 1}interior{media{emission 1density{spherical
density_map{[0rgb 0][.5rgb<1,.5>][1rgb 1]}turbulence.9}}}scale
<1,1,3>hollow}text{ttf"timrom""Warp".1,0translate<-1,-.1,2>}//  - Warp -

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