"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)

vrotate() simply rotates an object around a vector.

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.

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