Vectors you can rotate just as you would any other point but scales and
transforms are different. A transform changes the direction and length of
the vector and a scale just changes it's length. The thing to remember about
vectors is that they're just directions, nothing more. Although conceptually
you think of them as having position when associated with a vertex, they
have no position at all. It's important you try and get your head around
that basic concept.
> -----Original Message-----
> From: owner-xsi(at)Softimage.COM [mailto:owner-xsi(at)Softimage.COM] On
> Behalf Of Bernard Lebel
> Sent: 19 October 2006 14:29
> To: XSI(at)Softimage.COM
> Subject: Re: [script] Normals - not understanding
>
> Hi Aloys,
>
> I was not using the same operation!
>
> Anyway I thought that simply getting the normal orientation in object
> space, then to world space, would be enough for rotating nulls.
>
>
>
> Mathieu: thanks a lot for the explanation. If that made sense,
> well...... I got to do my homeworks. Once again :-(
>
>
> Bernard
>
>
> On 10/18/06, Aloys Baillet <aloys.baillet(at)gmail.com> wrote:
> > Hi Bernard,
> >
> > Normals are not points, they are vectors. You can't transform them
> > from object to world space using the same operations as for point
> positions.
> > You can read there for more info:
> > http://www.unknownroad.com/rtfm/graphics/rt_normals.html
> >
> > Cheers,
> >
> > Aloys
> >
> >
> > On 10/19/06, Mathieu Leclaire < mleclair(at)hybride.com> wrote:
> > > Of course... cross products... the cross product of 2 vectors will
> > > give
> > you
> > > the perpendicular vector. 2 vectors will form a plane unless they
> > > are both aligned (pointing in the same direction or in exact
> opposite directions).
> > So
> > > doing the cross product will give you the normal of that plane. So
> I
> > assign
> > > vY towards the global Y axis and I do the cross product of it with
> > > the normal vector giving me the correct vX vector. Then I do the
> > > cross product of that vX vector with the vZ (the normal) to get the
> > > correct vY. So basically, vY(0,1,0) acts like an up vector. vZ will
> > > point towards the normal and vY will be aligned with the up-vector.
> > > Normalize them and place them in the Rotation from axis and there
> > > you go. Does that make sense to you?
> > >
> > > Mathieu
> > >
> > > -----Original Message-----
> > > From: owner-xsi(at)Softimage.COM [mailto:owner-xsi(at)Softimage.COM]On
> > > Behalf Of Bernard Lebel
> > > Sent: Wednesday, October 18, 2006 3:53 PM
> > > To: XSI(at)Softimage.COM
> > > Subject: Re: [script] Normals - not understanding
> > >
> > >
> > > Nope, you are spot on Mathieu. That's exactly what I was trying to
> do.
> > >
> > > In hopes of understanding this more......
> > >
> > >
> > > Do you mind explaining why you did this?
> > >
> > > vZ = ovGlobalNormal;
> > > vY.Set(0, 1, 0);
> > > vX.Cross(vY, vZ);
> > > vY.Cross(vZ, vX);
> > >
> > >
> > > Thanks
> > > Bernard
> > >
> > >
> > > On 10/18/06, Mathieu Leclaire <mleclair(at)hybride.com> wrote:
> > > > I'm sorry... I'm not sure I understand what you are looking
> for...
> > > > did I anwser your question on my last reply or did I miss the
> point?
> > > >
> > > > -----Original Message-----
> > > > From: owner-xsi(at)Softimage.COM [mailto:owner-xsi(at)Softimage.COM]On
> > > > Behalf Of Bernard Lebel
> > > > Sent: Wednesday, October 18, 2006 3:11 PM
> > > > To: XSI(at)Softimage.COM
> > > > Subject: Re: [script] Normals - not understanding
> > > >
> > > >
> > > > I should add that the actual null rotation values correspond to
> > > > the normal values. However, the normal values are, from what I
> > > > see, very strange. For instance, to match a normal of a certain
> > > > vertex of values 40.0, 0.0, 40.0, I would have to use a rotation
> value of 0.0, 45.0, 0.
> > > >
> > > >
> > > > Bernard
> > > >
> > > >
> > > >
> > > > On 10/18/06, Bernard Lebel <3dbernard(at)gmail.com> wrote:
> > > > > Hi,
> > > > >
> > > > > I'm writing a script that extracts the normal vector of every
> > > > > point of a mesh. Then these vectors are mapped to world space.
> > > > > Finally, for each point, a null is created and the world vector
> > > > > is applied to its rotation.
> > > > >
> > > > > For a minority of normals, it works well, the null ends up with
> > > > > the right orientation. But for a majority of them, the null has
> > > > > an orientation that I have a hard time to figure out.
> > > > >
> > > > > If you create a sphere and run the code below, you'll see what
> I mean:
> > > > >
> > > > >
> > > > > import win32com
> > > > >
> > > > > xsi = Application
> > > > > xsimath = win32com.client.Dispatch( 'XSI.Math' )
> > > > >
> > > > > oMesh = xsi.selection(0)
> > > > > oMeshTransform = oMesh.kinematics.local.transform
> > > > >
> > > > > for oPoint in oMesh.activeprimitive.geometry.points:
> > > > >
> > > > > # Get global point normal direction
> > > > > ovGlobalNormal =
> > xsimath.mapobjectorientationtoworldspace (
> > > > > oMeshTransform, oPoint.normal )
> > > > >
> > > > > # Get New point position
> > > > > ovGlobalPosition =
> > xsimath.mapobjectpositiontoworldspace(
> > > > > oMeshTransform, oPoint.position )
> > > > >
> > > > > # create null
> > > > > oNull = xsi.activesceneroot.addnull()
> > > > >
> > > > > oNull.kinematics.local.rotx.value =
> > xsimath.radianstodegrees(
> > > > > ovGlobalNormal.x )
> > > > > oNull.kinematics.local.roty.value =
> > xsimath.radianstodegrees(
> > > > > ovGlobalNormal.y )
> > > > > oNull.kinematics.local.rotz.value =
> > xsimath.radianstodegrees(
> > > > > ovGlobalNormal.z )
> > > > >
> > > > > oNull.kinematics.local.posx.value =
> > ovGlobalPosition.x
> > > > > oNull.kinematics.local.posy.value =
> > ovGlobalPosition.y
> > > > > oNull.kinematics.local.posz.value =
> > ovGlobalPosition.z
> > > > >
> > > > >
> > > > >
> > > > > Any idea?
> > > > >
> > > > >
> > > > > Using XSI 5.11
> > > > >
> > > > >
> > > > > Thanks
> > > > > Bernard
> > > > >
> > > > ---
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> >
> >
> > --
> > Aloys Baillet - XSI Technical Director Character Dpt - Animal Logic
> > --
> ---
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