Hello,

I am new to this group and browsing through the messages, I find that I
am pleased you are all here. I have been using POV-Ray for some time
now. There is a problem that I have with the orthographic camera which I
could not find mentioned anywhere else.

The problem is as follows.

This works:
camera { orthographic location <0,0,-10> right <4,0,0> up <0,3,0>  }

This does not work:
camera { orthographic location <10,0,0> right <0,0,4> up <0,3,0>  }

Both should be possible, but the latter gives an error:
"Cannot use non-perpendicular camera vectors with vista buffer".
I worked around it by rotating the scene, but that is not a satisfactory
solution.

The system I am using is:
-Povray 3.1 for Windows
-Windows NT

Is there a way to get the second version of the camera
positioning to work? I find that most directions
and positions that deviate from the first version give the same error
message
even when the vectors are perpendicular.

Finally, the solution that is offered in the help file to add the
command "look_at" is also not satisfactory because that can rotate
the camera around it's own axis resulting in to a completely
different setting than "right" and "up" were set.

Regards,
Ralph

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Hi Ralph :

> This works:
> camera { orthographic location <0,0,-10> right <4,0,0> up <0,3,0>  }
> 
> This does not work:
> camera { orthographic location <10,0,0> right <0,0,4> up <0,3,0>  }
> 
> Both should be possible, but the latter gives an error:
> "Cannot use non-perpendicular camera vectors with vista buffer".
> I worked around it by rotating the scene, but that is not a satisfactory
> solution.
>
> Is there a way to get the second version of the camera
> positioning to work? I find that most directions
> and positions that deviate from the first version give the same error
> message
> even when the vectors are perpendicular.

You don't mention "direction" at all, and this is very important. The 
viewing direction has a default value of <0,0,1>, then the message must 
mean that "right"  is not perpendicular to default "direction". Both "up" 
and "right" need to be perpendicular to the viewing direction, I think.
So, perhaps you need also to specify "direction <-1,0,0>"  to override the 
default viewing direction.

  
-- 
Jaime Vives Piqueres

La Persistencia de la Ignorancia
http://www.ignorancia.org

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Thanks Jamie!

That was as accurate as fast :) It works now that I set the
direction vector. It is so much nicer to have the scene set and
just move the camera about.

All the time I was assuming silently that the orthographic
camera did not use the direction vector... now I know it does.
Furthermore, I would like to add that it will not even work for

camera { orthographic location <4.33013,5,-7.5>
                direction <-6.01900,-6.95016, 10.4252>
                right <3.72831,0,2.15254>
                up <-0.807203,2.79623,1.39812> }

but will for this:

camera { orthographic location <4.33013,5,-7.5>
               direction <-0.433012701892,-0.5,0.75>
               right <3.72831275528,0,2.15254237288>
               up <-0.807203389831,2.79623456646,1.39811728323> }

so 6 significant digits are not good enough some times.

Regards,
Ralph

Jaime Vives Piqueres wrote:

> You don't mention "direction" at all, and this is very important. The
> viewing direction has a default value of <0,0,1>, then the message must
> mean that "right"  is not perpendicular to default "direction". Both "up"
> and "right" need to be perpendicular to the viewing direction, I think.
> So, perhaps you need also to specify "direction <-1,0,0>"  to override the
> default viewing direction.

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Ralph Muench wrote:
> Furthermore, I would like to add that it will not even work for
[...]

  I think you are going the hard way... I prefer to think that up and right 
have nothing to do at all with camera position or direction, but rather 
with the "film" or "visualization window" size. I prefer to have it fixed 
at the default orientation, only sizing them for ratio purposes, and then  
using only location, direction (some prefer angle) and look_at to control 
the camera. It's much more easy this way for me, but I rarely need to 
accurately positioning the camera, tough.

-- 
Jaime Vives Piqueres

La Persistencia de la Ignorancia
http://www.ignorancia.org

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Jaime Vives Piqueres wrote:

> <...> I think you are going the hard way... I prefer to think that up and
> right
> have nothing to do at all with camera position or direction, but rather
> with the "film" or "visualization window" size. I prefer to have it fixed
> at the default orientation, only sizing them for ratio purposes, and then
> using only location, direction (some prefer angle) and look_at to control
> the camera. <...>

You are right. It is the hard way. Using the "position" and "look_at" vectors
is much simpler to imagine. But how do you work around the jump in orientation
from
camera { orthographic location <0,1,0.01> look_at <0,0,0> }
to
camera { orthographic location <0,1,0.00> look_at <0,0,0> }
?
That is the only reason I chose "up" and "right": to avoid discontinuities...
when the
camera is pointing in directions close to the y-direction. I'd gladly switch to

"position" and "look_at" if there was an easy way to get
round the jump (perhaps with angle? but when will the camera flip round?).

Regards,
Ralph

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"Ralph Muench" wrote:
> That is the only reason I chose "up" and "right":
> to avoid discontinuities... when the camera is
> pointing in directions close to the y-direction.
> I'd gladly switch to "position" and "look_at" if
> there was an easy way to get round the jump

Try looking at the sky vector.

Rune
--
3D images and anims, include files, tutorials and more:
Rune's World:    http://rsj.mobilixnet.dk (updated Jan 20)
POV-Ray Users:   http://rsj.mobilixnet.dk/povrayusers/
POV-Ray Webring: http://webring.povray.co.uk

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Ralph Muench wrote:
> 
> Thanks Jamie!
> 
> That was as accurate as fast :) It works now that I set the
> direction vector. It is so much nicer to have the scene set and
> just move the camera about.

> All the time I was assuming silently that the orthographic
> camera did not use the direction vector... now I know it does.
> Furthermore, I would like to add that it will not even work for

I think that it needs the direction vector for the direction, but it
ignores the magnitude with orthographic projection

Josh English
eng### [at] spiritonecom
http://www.spiritone.com/~english

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Josh, Rune and Jamie. Thanks for your input.
You have been a great help. I believe to have the
orthographic camera sorted out now :).
Regards,
Ralph

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