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Peter Popov wrote:
> If you mean you can skew an object by rotation, translation and
> scaling, I think you've been mislead. Mr. VanSickle is The One when it
> comes to manipulating the matrix keyword and I trust whatever he says
> on the subject, but this time I doubt he'd disagree. Then again, if I
> am wrong, I will learn something new :)
box{
0,1
rotate z*45
scale <1,2,1>
rotate z*-45}
PoD.
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On Tue, 23 May 2000 07:55:08 +0930, PoD <pod### [at] merlin netau> wrote:
>box{
> 0,1
> rotate z*45
> scale <1,2,1>
> rotate z*-45}
This is not what I had in mind. This only scales the local coordinate
axes but does not change the angle between them, as skewing does (I
think). Something like matrix <1,1,0,0,1,0,0,0,1,0,0,0> is more along
the lines of what I have in mind.
Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] usanet
TAG e-mail : pet### [at] tagpovrayorg
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Peter Popov wrote:
>
>
> This is not what I had in mind. This only scales the local coordinate
> axes but does not change the angle between them, as skewing does
This transform does indeed skew the object, but you'd have to use a bit of trig
to get the skewing along a specific axis.
--
Margus Ramst
Personal e-mail: mar### [at] peakeduee
TAG (Team Assistance Group) e-mail: mar### [at] tagpovrayorg
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On Tue, 23 May 2000 01:58:30 +0300, Margus Ramst <mar### [at] peakeduee>
wrote:
>> This is not what I had in mind. This only scales the local coordinate
>> axes but does not change the angle between them, as skewing does
>
>This transform does indeed skew the object, but you'd have to use a bit of trig
>to get the skewing along a specific axis.
I see, so shearing comes down to scaling along (an) axe(i)s which are
(is) not perpendicular to the local axes. Am I right in guessing that?
If so, thanks for clearing it up for me! If not, I'd be thankful if
you cleared it up for me <grin>
Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] usanet
TAG e-mail : pet### [at] tagpovrayorg
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Peter Popov wrote:
>
> I see, so shearing comes down to scaling along (an) axe(i)s which are
> (is) not perpendicular to the local axes. Am I right in guessing that?
> If so, thanks for clearing it up for me! If not, I'd be thankful if
> you cleared it up for me <grin>
>
Well, yes. That's one way of looking at it. Of course, matrix shearing
approaches the problem from a different perspective - the scaling of a point
along one global axis is (linearly) bound to the distance of this point along
another global axis. E.g. when Point.x increases, the multiplier (scale) of
Point.y increases.
--
Margus Ramst
Personal e-mail: mar### [at] peakeduee
TAG (Team Assistance Group) e-mail: mar### [at] tagpovrayorg
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Peter Popov wrote:
>
> On Mon, 22 May 2000 17:46:55 +0200, "Rune" <run### [at] inamecom>
> wrote:
>
> >You can do that with rotate, scale and translate too. Actually I would guess
> >that any transformation can be done using those. Not that I need it... :-)
>
> If you mean you can skew an object by rotation, translation and
> scaling, I think you've been mislead. Mr. VanSickle is The One when it
> comes to manipulating the matrix keyword and I trust whatever he says
> on the subject, but this time I doubt he'd disagree. Then again, if I
> am wrong, I will learn something new :)
My matrix page does not explicitly spell this out, but shearing can
be done with the proper combination of rotate, non-uniform scale, and
another rotation. It is far easier to use a matrix. I would have
whipped up some macros for shearing, but the many different ways that
shearing can be specified makes it troublesome to decide how the syntax
should work.
Regards,
John
--
ICQ: 46085459
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