What exactly does it mean??
It seems to happen when using the orthographic. Adjusting the angle helps
fixing it somehow. To my understanding changing angle doesn't change the
vector direction but the vector size. What am I understanding wrong..??
When it says camera vectors, does it mean direction, up, and right??

camera {    // This one posts a warning
  orthographic
  angle 40
  location < -1500,1000,-1600>
  look_at <-100,-200,500>
}

camera {    // This one doesn't
  orthographic
  angle 35
  location < -1500,1000,-1600>
  look_at <-100,-200,500>
}

Thanx
J.

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Just want to add more to it..
Sometimes, without "angle" it doesn't warn.. Sometimes, it does, then you
add "angle" and it's OK..
Or sometimes, you have "angle" it's not OK.. and you get rid of "angle" it's
OK again.. reading help within the program doesn't help at all for me.. I'm
still quite blank on "up" and "right"..


"MrJuB" <sas### [at] mtuthaicoth> wrote in message
news:web.3feb9386fc757a645674f9150@news.povray.org...
> What exactly does it mean??
> It seems to happen when using the orthographic. Adjusting the angle helps
> fixing it somehow. To my understanding changing angle doesn't change the
> vector direction but the vector size. What am I understanding wrong..??
> When it says camera vectors, does it mean direction, up, and right??
>
> camera {    // This one posts a warning
>   orthographic
>   angle 40
>   location < -1500,1000,-1600>
>   look_at <-100,-200,500>
> }
>
> camera {    // This one doesn't
>   orthographic
>   angle 35
>   location < -1500,1000,-1600>
>   look_at <-100,-200,500>
> }
>
> Thanx
> J.
>

Post a reply to this message

On Thu, 25 Dec 2003 20:48:54 EST, "MrJuB" <sas### [at] mtuthaicoth>
wrote:

>What exactly does it mean??

It means that up right and direction are not perpendicular. While POV
will have no problem rendering the picture (unless two of them
coincide), the vista buffer depends on orthogonal camera vectors and
will be switched off.

If you manually specify your up and right vectors, make sure you give
them a proper direction (pun intended). For example this is a very
common mistake:

camera {
  location ...
  look_at ...
  right 16/9   // or 2.35 or 5/3 etc.
}


Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] vipbg
TAG      e-mail : pet### [at] tagpovrayorg

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But what if I'm not explicitly specifying up right and direction vectors..
something like what I showed..

camera {    // This one posts a warning
  orthographic
  angle 40
  location < -1500,1000,-1600>
  look_at <-100,-200,500>
}

camera {    // This one doesn't
  orthographic
  angle 35
  location < -1500,1000,-1600>
  look_at <-100,-200,500>
}


can you tell what my up right and direction vectors are exactly in each
one?? Aren't they the same because "angle" only altering the sizes of the
vectors not the directions?? I can't tell if they aren't perpendicular if I
don't know what they are..

Thanx again

"Peter Popov" <pet### [at] vipbg> wrote in message
news:09snuvckvabo7sbidlj269h75uhfor4oh9@4ax.com...
> On Thu, 25 Dec 2003 20:48:54 EST, "MrJuB" <sas### [at] mtuthaicoth>
> wrote:
>
> >What exactly does it mean??
>
> It means that up right and direction are not perpendicular. While POV
> will have no problem rendering the picture (unless two of them
> coincide), the vista buffer depends on orthogonal camera vectors and
> will be switched off.
>
> If you manually specify your up and right vectors, make sure you give
> them a proper direction (pun intended). For example this is a very
> common mistake:
>
> camera {
>   location ...
>   look_at ...
>   right 16/9   // or 2.35 or 5/3 etc.
> }
>
>
> Peter Popov ICQ : 15002700
> Personal e-mail : pet### [at] vipbg
> TAG      e-mail : pet### [at] tagpovrayorg

Post a reply to this message

MrJuB wrote:

> camera {    // This one posts a warning
>   orthographic
>   angle 40
>   location < -1500,1000,-1600>
>   look_at <-100,-200,500>
> }
> 
> camera {    // This one doesn't
>   orthographic
>   angle 35
>   location < -1500,1000,-1600>
>   look_at <-100,-200,500>
> }


That sounds like a bug to me. According to the documentation, angle only
changes the length of the direction vector, location is a fundamental
camera parameter on its own (independent of up, right, direction), and
look_at only rotates the camera, none of which should change the angles
between up, right and direction.

Furthermore, the warning disappears if you scale location and look_at
smaller:

camera {    // no warning  orthographic  angle 40  location <
-150,100,-160>  look_at <-10,-20,50>}

Adding some debug code outputting the camera vectors to the POV-Ray source
shows that it is indeed a precision issue: In the first case,

  right = <1692.664786, 0.000000, -1128.443191>
  up = <364.320650, 1381.382466, 546.480975>
  direction = <0.915289, -0.784534, 1.372934>
  right.up = -1.589516e-10
  right.direction = -1.110369e-13
  up.direction = 1.941461e-13
  epsilon = 1.000000e-10

i.e. because right and up are so long, |right.up| > epsilon. Maybe the
vectors should be normalized before taking their dot product, or something
like this.

 -Christian

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> camera {    // no warning  orthographic  angle 40  location <
> -150,100,-160>  look_at <-10,-20,50>}

Whoops, that should read:

camera {    // no warning
  orthographic
  angle 40
  location <-150,100,-160>
  look_at <-10,-20,50>
}

Pan's "rewrap" messed it up...

Post a reply to this message

In article <pan### [at] gmxch> , Christian Walther 
<cwa### [at] gmxch>  wrote:

> i.e. because right and up are so long, |right.up| > epsilon. Maybe the
> vectors should be normalized before taking their dot product, or something
> like this.

Which would introduce other precision problems :-(  Probably scaling EPSILON
up rather than the vectors down would help.  Any any case, the warning as
displayed is valid because they vectors are really not perpendicular.  So
they scene should be adjusted to use shorter vectors, which result in more
available precision.

    Thorsten

____________________________________________________
Thorsten Froehlich, Duisburg, Germany
e-mail: tho### [at] trfde

Visit POV-Ray on the web: http://mac.povray.org

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In article <3febac01@news.povray.org> , "Sasathorn Phaspinyo" 
<sas### [at] mtuthaicoth> wrote:

> Just want to add more to it..
> Sometimes, without "angle" it doesn't warn.. Sometimes, it does, then you
> add "angle" and it's OK..
> Or sometimes, you have "angle" it's not OK.. and you get rid of "angle" it's
> OK again.. reading help within the program doesn't help at all for me.. I'm
> still quite blank on "up" and "right"..

Maybe you need to brush up your math skills.  The camera logic is not
trivial to understand without sufficient understanding of vector math.

    Thorsten

____________________________________________________
Thorsten Froehlich, Duisburg, Germany
e-mail: tho### [at] trfde

Visit POV-Ray on the web: http://mac.povray.org

Post a reply to this message

Thorsten Froehlich wrote:
> In article <pan### [at] gmxch> , Christian Walther
> <cwa### [at] gmxch>  wrote:
> 
>> i.e. because right and up are so long, |right.up| > epsilon. Maybe the
>> vectors should be normalized before taking their dot product, or
>> something like this.
> 
> Which would introduce other precision problems :-( Probably scaling
> EPSILON up rather than the vectors down would help.

Right, the numerical error would probably be smaller if one calculated the
dot product first and then scaled it down (or epsilon up) by the product
of the vector lenghts. But as far as I see in the source, the dot product
calculation at that place is only used to decide whether to show the
warning, so numerical accurracy shouldn't be a big concern. But the
present code is flawed because the bounds for the angle (within which it
is accepted as "perpendicular") depend on the lenghts of the vectors.

> Any any case, the warning as displayed is valid because they vectors are
> really not perpendicular.

Sure, but they are very close to perpendicularity. Sufficiently close not
to require a warning, IMHO. And as you can see, it confuses people. Maybe
it would help if the warning would include some numbers, so that one could

camera definition), or if it's just numerical error. Additionally, if
there is an error in the camera definition, one would probably find it
faster if one knew the angles.

 -Christian

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news:web.3feb9386fc757a645674f9150@news.povray.org...

> When it says camera vectors, does it mean direction, up, and right??

Since nobody said it clearly: orthographic cameras are much easier to deal
with using the up and right vectors since they define the size of the
viewing area (in POV units).
#declare Size=10;
camera{
    orthographic
    location ...
    up y*Size
    right x*Size*image_width/image_height
    look_at ...
}


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