On Thu, 15 Aug 2013 18:16:51 +0200, Anthony D. Baye  
<Sha### [at] spamnomorehotmailcom> wrote:

> "Nekar Xenos" <nek### [at] gmailcom> wrote:
>> I am trying to duplicate the camera angle in a scene with a box mapped
>> with the image, but when I use certain camera positions and look
>> combinations, it rotates the image along the z axis. It seems to happen
>> when the Camera position and look position don't have the same y value.
>>
>> How can i fix this?
>>
>> here is a stripped down version. If the "doesn't work' part is commented
>> out it works fine.
>>
>> I must admit, I don't always know when to use Reorient_Trans() vs
>> vrotate() vs VAngleD() and even less how to use them. It gets confusing.
>
> Reorient_Trans() rotates an object so that a given axis is aligned with  
> another
> axis by rotating the object around an axis perpendicular to both.
>
> e.g. reorienting the object to align its x axis with it's z axis would  
> rotate it
> around y.  This is, of course, an extremely trivial example, but you  
> could also
> use it to align an axis with a given vector (not sure if it needs to be a
> unit-vector or not)

So this is the correct one to use.

>
> vrotate() simply rotates an object around a vector.
Thanks Anthony. The docs don't specify that it is an abject that gets  
rotated.

>
> VAngle() and VAngleD() compute the angle between two vectors, the former
> returning an angle in radians, the latter returning an angle in degrees.
>>
>>
>> //-----------------------------------//
>> // begin code
>> #version 3.7;
>>
>> global_settings {  max_trace_level 5 assumed_gamma 1}
>>
>>
>> #include "Transforms.inc"
>>
>>
>> //works:
>> #declare CamPos= <0.5, 1.5,4.5 >;
>> #declare CamLook= <1.3,1.5,0>;
>> ///////////////////////////////////
>>
>> // doesn't work:
>> #declare CamPos= <0.5, 1.5,4 >;
>> #declare CamLook= <1.3,1.2,0>;
>> //////////////////////////////////
>>
>> #declare CamDirect=<0,0,1>;
>> #declare CamWidth=image_width;
>> #declare CamHeight=image_height;
>>
>> #declare ColMapPig=pigment {image_map { png "test.png" }
>>                              translate -0.5*(x+y)
>>                              scale <CamWidth/CamHeight,1,1>*2
>>                              }
>>
>>
box{<-CamWidth/CamHeight,-1,CamDirect.z>,<CamWidth/CamHeight,1,CamDirect.z+0.001>//}
>>
>>                          texture {
>>                                  pigment {ColMapPig}
>>                                  finish { ambient 1 diffuse 1}
>>                                  }
>>
>>
>>                             translate CamDirect
>>                             Reorient_Trans(z, (CamLook-CamPos))
>>
>>                             translate CamPos
>>                             }
>>
>> #declare ColMap="test.png"
>>
>> ///////////////////////////////////////////////////
>>
>> camera {
>>          location  CamPos
>>          direction CamDirect
>>          right   x*image_width/image_height
>>          look_at CamLook
>>          }
>> // End code
>> //-------------------------//
>>
>>
>> //--
>> -Nekar Xenos-
>
> I agree with Christian that you need to specify the up vector in your  
> camera
> definition.  My default camera is usually something like this: (actually  
> a lot
> like yours)
>
> camera {
>     perspective
>     location locVect
>     up y
>     right x*(image_width/image_height)
>     look_at lookVect
>     }
>
> regards,
> A.D.B.
>

This makes no difference. In this case my object needs an "up y" option :S

-- 
-Nekar Xenos-

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