RE: [Algorithms] Extracting scale from matrix

[Jon A. <jan...@on...>]

Thanks.  I found it here:
http://www.acm.org/tog/GraphicsGems/category.html

which incidently lists it as Graphics Gems II, p. 320-323... =)

Jon



At 11:51 AM 9/7/2000 -0700, you wrote:
>Isn't there a DecomposeMatrix routine in one of the Graphics Gems?
>
>Pass it a 4x4 matrix and it returns rotation, scale, translation,
>shear and probably something more...
>
>...yeah, it's at page 207 of Graphics Gems 4.
>
>-Blake
>
>
>-----Original Message-----
>From: Neal Tringham [mailto:ne...@ps...]
>Sent: Thursday, September 07, 2000 10:18 AM
>To: gda...@li...
>Subject: Re: [Algorithms] Extracting scale from matrix
>
>
>
>De: Jon Anderson [mailto:jan...@on...]
>
> >Are there any good tricks for extracting the scale (x, y, z)  from a 4x4
> >matrix?  It seems pretty trivial to do it for matrices that consist of
> >rotations about a single axis, but I'm having problems doing it for more
> >complex matrices.
>
>If your matrix contains only rotation, scale and translation information,
>could you extract the scale factors by comparing the length of the basis
>vectors to the length of the normalised basis vectors?
>
>Note that (even if this works:-)) I don't believe it would allow you to
>distinguish between a negative sign in a scale factor (a "mirror") and a
>rotation, i.e. it would only allow you to extract the magnitude of the scale
>factors, not their signs.
>
>Curious as to people's comments on this...
>
>Neal Tringham (Sick Puppies)
>
>ne...@ps...
>ne...@em...
>
>
>
>
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