POV-Ray : Newsgroups : povray.advanced-users : Skewness (long) : Re: Skewness (long) Server Time23 Jun 2024 08:04:27 EDT (-0400)
 Re: Skewness (long)
 From: Francois LE COAT Date: 5 Oct 2018 09:50:34 Message: <5bb76c2a\$1@news.povray.org>
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Hi,

Bald Eagle writes:
> I think what you want is just called "Shear".
>
> http://www.f-lohmueller.de/pov_tut/trans/trans_450e.htm
>
> Most times when people refer to "skew" it's more of a corkscrew type of

> deformation - typically encountered 50 times when trying to get a singl
e
> straight 2x4 out of a pallet of lumber at a Big Box store.  :|

This "Shear" transformation is very interesting ! It's a 3D
transformation in space. We are very close to an answer to the problem.

I'm speaking of a 2D projective transformation in the image plane, that
is rendered when two images of the same scene, are viewed from different
viewpoints. Here is two real successive aerial images taken with the
same camera :

<http://eureka.atari.org/perspective.gif>

They are linked with the 8 projective transformation parameters :

Tx = -30.6 pixels
Ty = 22.7 pixels
Tz = -13.5 pixels

(Rx, Ry, Rz) are (yaw, pitch, roll) Euler angles in 3D space, and
(Tx, Ty, Tz) the 3 translations in 3D space. The two supplementary
parameters, "Shear" or "Skew" (Sx, Sy) are two perspective angles.
The global "Correlation = 83.7%" coefficient tells about good matching.

The corresponding mosaic is shown to illustrate the geometric transform.

Is the "Shear" transform applicable to the POV-Ray camera properties ?
I mean, "translate <Tx, Ty, Tz>" and "rotate <Rx, Ry, Rz>" are
applicable to the camera properties, to render movement of the camera.
Can I apply these two "matrix" transforms to modify the perspective ?

Thanks a lot for the very positive help =)

Best regards,

--

<http://eureka.atari.org/>
```