visualpython-users

[Visualpython-users] rotation and axis

[Kuzminski, S. R <SKu...@fa...>]

Hi,

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If I rotate a shape, I seem to get an odd axis value after the
rotation..

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here is a simple program...

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from visual import *

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shape =3D cylinder( pos=3D( 0, 0, 0 ),

                  length=3D.1,

                  radius=3D.01 )

print 'before', shape.axis

shape.rotate( angle=3Dpi/2, axis=3D(0,0,1))

print 'after', shape.axis

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and here is the output..  shouldn't 'after' be [0, 0.1, 0]  am I missing
something?

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C:\>python tmp.py

Visual-2003-10-05

before [0.1 0 0]

after [6.12303e-018 0.1 0]   <-- ???

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thanks,

Stefan

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Re: [Visualpython-users] rotation and axis

[Jonathan B. <jdb...@un...>]

Kuzminski, Stefan R wrote:

> Hi,
>
> If I rotate a shape, I seem to get an odd axis value after the rotation=
..
>
> here is a simple program=85
>
> from visual import *
>
> shape =3D cylinder( pos=3D( 0, 0, 0 ),
>
> length=3D.1,
>
> radius=3D.01 )
>
> print =91before=92, shape.axis
>
> shape.rotate( angle=3Dpi/2, axis=3D(0,0,1))
>
> print =91after=92, shape.axis
>
> and here is the output.. shouldn=92t =91after=92 be [0, 0.1, 0] am I mi=
ssing=20
> something?
>
> C:\>python tmp.py
>
> Visual-2003-10-05
>
> before [0.1 0 0]
>
> after [6.12303e-018 0.1 0] =DF ???
>
> thanks,
>
> Stefan
>

The algorithms for generalized rotation unavoidably introduce a tiny=20
error (this example shows an error 18 orders of magnitude smaller than=20
the value!). Keep in mind that since pi cannot be represented exactly in=20
a computer, neither is pi/2 nor is rotating by pi/2.

HTH,
Jonathan Brandmeyer