Awesome, thanks!



On 9/28/2018 12:27 AM, clipka wrote:
> Am 28.09.2018 um 03:27 schrieb Mike Horvath:
>> Two important questions I have (that may not be explained in the docs),
>> is how to convert a 3x3 rotation matrix to POV-Ray syntax, and how to
>> determine the inverse matrix?
> 
> given a matrix
> 
>       / a  b  c \
>      (  d  e  f  )
>       \ g  h  i /
> 
> you have to specify either
> 
>      matrix < a, b, c,
>               d, e, f,
>               g, h, i,
>               0, 0, 0 >
> 
> or
>      matrix < a, d, g,
>               b, e, h,
>               c, f, i,
>               0, 0, 0 >
> 
> The order depends on whether the original matrix is specified in
> "mathematical" or "computer graphics" style - they're mirrored along the
> diagonal. Can't remember which one POV-Ray uses.
> 
> Determining the inverse /transformation/ is simple:
> 
>      #declare Foo = transform { matrix < ... > }
>      #declare FooInv = transform { Foo inverse }
> 
> Actually getting at the corresponding matrix is possible by applying the
> inverted transformation to the axis vectors.
>

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Le 28/09/2018 à 03:27, Mike Horvath a écrit :
> Two important questions I have (that may not be explained in the docs), 
> is how to convert a 3x3 rotation matrix to POV-Ray syntax, and how to 
> determine the inverse matrix?
> 
> 
> Mike



you only have to input a 3x4 ( column x line), but the math beyond use a 
4x4 matrix with a fourth column set to
{ 0,
   0,
   0,
   1 }
(the 4x4 is important, when combining transformation, a 4x4 * 4x4 -> 
4x4, whereas it make no sense with 3x4 )

The fourth line is the translation

http://wiki.povray.org/content/Reference:Transformations#Matrix

To input a 3x3 rotation matrix
( A B C
   D E F
   G H I )

into povray, it's "simply"

( A B C
   D E F
   G H I
   0 0 0 )

With A to I being the naughty variations of 
"cos(phi)*sin(theta)*cos(gamma)" as usual.

To get the inverse matrix, I'm lazy:

#declare Forward = transform { matrix < .... > } };
#declare Backward = transform { Forward inverse };

As long as the forward matrix is not degenerated, that should do the job.

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Le 28/09/2018 à 01:40, Mike Horvath a écrit :
> It would be nice to be able to set vector components like this:
> 
>      #local tPrjB1.z = max(min(tPrjB1.z,1),-1);
> 
> Are there any plans to do this in the future?
> 
> 
> 
> Mike

you could use the following:

#local P = <p.x, P.y, max(min(P.z),1),-1)>;

Make that a set of macro, and voila.

#macro BoundZ( V )
<V.x, V.y, max(min(V.z),1),-1) >
#end

#local P = BoundZ(P);

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