vrml transformations 
Author Message
 vrml transformations

   Hi, I'm having a bit of trouble with the "scaleOrientation" and "center"
fields in the Transform nodes.  The spec says:

Given a 3-dimensional point P and Transform node, P is transformed into
point P' in its parent's coordinate system by a series of intermediate
transformations. In matrix transformation notation, where C (center), SR
(scaleOrientation), T (translation), R (rotation), and S (scale) are the
equivalent transformation matrices,

    P' = T C R SR S -SR -C P

for the -SR  rotation matrix, am I supposed to negate the angle only or also
the x,y,z values?

I have is all the above 4x4 transformation matrices but only the
scaleOrientation and center
values are messing things up (when not default values).   i.e. I can do
'regular' rotate/translate/scale ok

Thanks

Larry



Sat, 18 Aug 2001 03:00:00 GMT  
 vrml transformations

Quote:

>    Hi, I'm having a bit of trouble with the "scaleOrientation" and "center"
> fields in the Transform nodes.  The spec says:

> Given a 3-dimensional point P and Transform node, P is transformed into
> point P' in its parent's coordinate system by a series of intermediate
> transformations. In matrix transformation notation, where C (center), SR
> (scaleOrientation), T (translation), R (rotation), and S (scale) are the
> equivalent transformation matrices,

>     P' = T C R SR S -SR -C P

> for the -SR  rotation matrix, am I supposed to negate the angle only or also
> the x,y,z values?

You only need to worry about this if you are writing a vrml viewer
(the spec is describing what conforming browsers do). But anyway...

You need to invert the SR rotation matrix, that is, undo the rotation.
You can do that by either negating the angle or negating the axis, not
both.

Quote:

> I have is all the above 4x4 transformation matrices but only the
> scaleOrientation and center
> values are messing things up (when not default values).   i.e. I can do
> 'regular' rotate/translate/scale ok

> Thanks

> Larry

--
Chris Morley



Sat, 18 Aug 2001 03:00:00 GMT  
 
 [ 2 post ] 

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