I used
simpleU.getViewingPlatform().getViewPlatformTransform().getTransform() to
get the current viewPlatformTransform. I was wondering would this be the
same as using viewPlatform.getLocaltoVworld(vw_tx)?
Thanks!
Lan
At 10:23 AM 9/3/2001 -0500, you wrote:
>Thanks Justin
>
>Your explanation helped me a lot to understand these issues. I'll go over my
>source code and check the matrix out....
>I'll let you know how it worked.
>
>Thank you again for your time.
>
>
>
>
>----- Original Message -----
>From: "Justin Couch" <[EMAIL PROTECTED]>
>To: "Juan Miguel" <[EMAIL PROTECTED]>
>Sent: Friday, August 31, 2001 1:23 AM
>Subject: Re: Hi justin
>
>
> > G'day Juan,
> >
> > > I need a vector known as UP and it's often represented as a unit
>vector, in
> > > order to set the orientation of the camera.
> > > I also need where camera is looking at... the focus point.
> >
> > So what you need here is values based on where the camera is currently
> > looking, rather than trying to set the camera in a particular direction.
> >
> > What you need to do is get the transform of the VP relative to the world
> > coordinates first. This is done by calling getLocalToVworld() of the
> > ViewPlatform.
> >
> > Transform3D vw_tx = new Transform3D();
> > viewPlatform.getLocaltoVworld(vw_tx);
> >
> > This gives you transformation information that will point everything to
> > world coordinates from whatever local coordinate system your camera is
> > in. Because this is only a transformation it does not contain any real
> > information directly. In order to get real information you use this
> > matrix to transform something else. So how do you get an Up vector from
> > this? Well you have to start with the assumption that "up" is along the
> > positive Y axis (right handed coordinate system). Even if your camera is
> > looking at the world upside-down, as far as the camera is concerned, up
> > is still along it's local +Y axis. What has changed is the parent
> > transformation. To find out what your local Y axis is in world
> > coordinates, you apply the world transform to a vector that points along
> > the local Up direction - ie (0, 1, 0).
> >
> > Vector3d up_dir = new Vector3d(0, 1, 0);
> > vw_tx.transform(up);
> >
> > up_dir vector now contains the true direction of the camera's "up"
> > direction in world coordinates.
> >
> > You can now apply these same principals to any other information you
> > need. For example, a viewplatform always points along the -Z axis in
> > it's local coordinate system. To find out which direction it is really
> > looking, transform the vector (0, 0, -1) and you have your answer.
> >
> > --
> > Justin Couch http://www.vlc.com.au/~justin/
> > Freelance Java Consultant http://www.yumetech.com/
> > Author, Java 3D FAQ Maintainer http://www.j3d.org/
> > -------------------------------------------------------------------
> > "Humanism is dead. Animals think, feel; so do machines now.
> > Neither man nor woman is the measure of all things. Every organism
> > processes data according to its domain, its environment; you, with
> > all your brains, would be useless in a mouse's universe..."
> > - Greg Bear, Slant
> > -------------------------------------------------------------------
> >
> >
> >
>
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Lan Wu-Cavener
Research Associate and Programmer
Dept. of Landscape Architecture
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