Re: [ggt-devel] Problems with Quats and scales on Matrix44f

[kevin m. <ke...@su...>]

That's right.  When we set a scale matrix, we set the diagonals in the
upper left 3x3.  then when we rotate it, we take the coordinate axes (the
3x3 that makes x, y, and x axis vectors) and rotate...   essentially, that
scale is still in there, so taking the length of each axis should give the
scale for each axis.  I don't think they have to all be the same scale.

good luck.

> Thanks Kevin. That is what I discovered and the solution that I
> implemented as well. Everything works great once I grab scale out of the
> matrix before creating the quat. And just to verify, when grabbing scale
> out of a 4x4 you take the length of each of the first 3 column vectors?
> Thanks again.
>
> Doug
>
>> *--*---*---*----*-----*------*------*-----*----*---*---*--*
>> Kevin Meinert                         /_/
>> http://www.subatomicglue.com                    \        /
>>                                                \/  __    \/
>>                                                    \__
>>                                             \_\
>>
>>
>>>Hello,
>>>     I am using gmtl 0.4.9. If I try to create a quat from this matrix I
>>>get the following:
>>>
>>>| 0.5 -0.866025 0 0 |
>>>| 0.866025 0.5 0 0 |
>>>| 0 0 1 0 |
>>>| 0 0 0 1 |
>>>
>>> quat
>>>(0, 0, 0.5, 0.866025)
>>>
>>>Which gives me the correct end rotation. Now, if I take the same matrix
>>>from above and apply a scale of 3 I get the following:
>>>
>>>| 1.5 -2.59808 0 0 |
>>>| 2.59808 1.5 0 0 |
>>>| 0 0 3 0 |
>>>| 0 0 0 1 |
>>>
>>> quat
>>>(0, 0, 0.981981, 1.32288)
>>>
>>>Which ends up over rotating by what appears to be a few degrees. It is
>>> my
>>>understanding that I should be able to create a quat with a matrix that
>>>does have scale on it, correct?
>>>
>>>Thanks for the help.
>>>
>>>Doug
>>>
>>>
>>>
>
>
> -------------------------------------------------------
> This SF.Net email is sponsored by the 'Do More With Dual!' webinar
> happening
> July 14 at 8am PDT/11am EDT. We invite you to explore the latest in dual
> core and dual graphics technology at this free one hour event hosted by
> HP,
> AMD, and NVIDIA.  To register visit http://www.hp.com/go/dualwebinar
> _______________________________________________
> ggt-devel mailing list
> ggt...@li...
> https://lists.sourceforge.net/lists/listinfo/ggt-devel
>