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...

Thanks again!

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...

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In article <422eb8bb$1@news.povray.org>,
 Sascha Ledinsky <sas### [at] userssourceforgenet> wrote:

> That should work, but I suspect it will lead to the same result if the 
> matrix is somehow not accurate enough...

No. Since the camera vectors are calculated by POV in this case, they 
will be perpendicular.

-- 
Christopher James Huff <cja### [at] gmailcom>
POV-Ray TAG: <chr### [at] tagpovrayorg>
http://tag.povray.org/

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In article <422ebbe7$1@news.povray.org>,
 Sascha Ledinsky <sas### [at] userssourceforgenet> wrote:

> But still, isn't the test POV performs too strict?

No. The test does not cause any problems that can't be fixed by using 
correct input. This is a very simple, minor problem which occurs very 
rarely and has a simple fix and several possible workarounds.

-- 
Christopher James Huff <cja### [at] gmailcom>
POV-Ray TAG: <chr### [at] tagpovrayorg>
http://tag.povray.org/

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Christopher James Huff wrote:
> In article <422eb8bb$1@news.povray.org>,
>  Sascha Ledinsky <sas### [at] userssourceforgenet> wrote:
> 
> 
>>That should work, but I suspect it will lead to the same result if the 
>>matrix is somehow not accurate enough...
> 
> 
> No. Since the camera vectors are calculated by POV in this case, they 
> will be perpendicular.
> 

I've found the problem and it does work now with the matrix keyword as well.
I should have checked my code earlier. Again, sorry!

-sascha

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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

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

Sort of... I don't know if it can be considered as a bug: The double 
precision 4x4 matrix class (Matrix4d) has a setRotationScale() method 
that takes a Quaternion as argument - either float (Quat4f) or double 
(Quat4d). The thing is, if you use a float quaternion on the double 
matrix, it seems that it does not re-normalize the quaternion after 
conversion to doubles.
Now I do

public void setOrientation(Quat4f orient_float) {
	Quat4d orient_double = new Quat4d(orient_float);
	orient_double.normalize();
	matrix.setRotation(orient_double);
}

which fixes the problem...

I'm not sure if Sun's official J3D package has the same problems - I'm 
using it in an open source project and so I'm forced to use an 
"inofficial" javax.vecmath package :-(

POV-Ray is happy with the new truly double-precision matrix, so I'm 
happy too :-)

Thanks again,
-Sascha

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