Sascha Ledinsky <sas### [at] userssourceforgenet> wrote:
> Thank you!
>
> To be honest, I did not know how to quickly check if the matrix is
> correct, and since the resulting images looked right... :-/
>
> I have found the problem: The quaternion used to compute the matrix uses
> single precision floats. The fix was to first create a double-precision
> quaternion from it, then re-normalize that and feed the double-precision
> quaternion into the matrix...

Ok, so it was the Java3D package that used single precision floats ?

Btw.: I hope that you spotted my error in this part of my code:

#declare vN1 = vnormalize(vR1);
#declare vN2 = vnormalize(vcross(vN1, vR2));
#declare vN3 = vcross(vN2, vN1);


It should be:

#declare vN1 = vnormalize(vR1);
#declare vN3 = vnormalize(vcross(vN1, vR2));
#declare vN2 = vcross(vN3, vN1);


Btw.: I also recommend that you google for the "Gram-Schmidt process".


> Thanks again!

I'm glad that I could be of any help to you.


> But still, isn't the test POV performs too strict?
> I understand that POV-Ray must use double precision math for most
> operations, but would, in this case, the single-precision matrix really
> break the vista buffer?
> This will enforce all external applications that are used to create
> POV-scenes to use double-precision math throughout, and I don't know if
> it is available in all (script) languages...

I don't have any strong opinions regarding this. (And I don't really know if
such a matrix could cause any problems with the vista buffer.)

You may have a point, but if I had this problem myself, I would just
"correct" the matrix "manually" with a few lines of POV-script.

--
Tor Olav
http://subcube.com

Post a reply to this message