"Christoph" <nomail@nomail> wrote:
> hello everybody!
>
> i am trying to use povray to generate test images for a camera calibration
> algorithm. the documentation suggests that the right and up vectors define
> the image plane, while the direction vector gives the distance from the pinhole
> to the image plane, ie the focal length. this agrees with the experimental fact
> that multiplying right,up and direction by a common factor does not change the
> image.
>
> my code looks like this:
>
>  camera
>  {
>   perspective
>
>   //image plane
>   right x * 0.01
>   up y/aspectRatio * 0.01
>
>   //focal length
>   direction <0,0,1> * 0.012
>
>   location <0,0,-1>
>   look_at <0,0,0>
>  }
>
> the calibration target is located at <0,0,0>.
>
> i define one povray unit to be one meter. so i should get an image plane of 10
> mm x 7.5 mm and a focal length of 12 mm. the image is rendered at a resolution
> of 800 x 600, so an individual pixel should be 0.0125 mm square. feeding all
> this into the calibration algorithm i get the following results:
>
> camera location:
> Tx = +0.547160,   Ty= -1.032746,   Tz = +1998.616576  [mm]
>
> camera rotation:
>  +1.000000  +0.000008  +0.000013
> M = -0.000008  +1.000000  +0.000265
>  -0.000013  -0.000265  +1.000000
>
> focal length:
> f = 11.991322  [mm]
>
> basically all is well except the z translation is twice the expected value.
> does anyone know where that factor 2 might come from?
>
> thanks
> /christoph

ok after checking the code 17 times i have to admit it was my mistake,
the calibration target was scaled by 0.5. sorry.

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