Jung,
the mapping from world to screen is always possible within the camera's
frustum, but the inverse is not true. It means that not every pixel of the
screen has a map into world coordinates. Even if a point within the screen
coordinates has a world mapping point, you can't actually know exactly which
point it is if you don't constrain the Z value of the point in world. Thats
because infinity points in world can map to a same point within the screen
coordinate. So, if you're trying to make some sort of "Arcball" or Trackball
feature using screen coordinates I can say that you don't need to convert
those screen point into world points.. you just need a map from screen space
to a open ball in R^3 using (centered at origin 0,0,0), for example,
spherical coordinates (two angles)....
to map from x,y into two angles (azimuth and zenith) you can do something
like this:
azimuth = ( 2*( x / screen_width ) - 1 ) * PI
zenith = ( 2*( y / screen_height ) - 1 ) * (PI / 2)
I've just came up with this mapping now, the're are many ways to build a
trackball feature, thats just only an idea... to map the two angles above
into a world vector within the open ball you can use:
[image: x][image: =][image: rcosthetasinphi] (4)
[image: y][image: =][image: rsinthetasinphi] (5)
[image: z][image: =][image: rcosphi.]
where r is an arbitrary ray of the ball (the biggest the ray the smallest is
the rotation sensitivity)
Hope it helps....
On Sat, Jul 5, 2008 at 3:06 AM, Jung Lee <[EMAIL PROTECTED]> wrote:
> Dear OpenSG Users,
>
> I found most of the solutions for my problems with OpenSG in this user
> forum! Thank you!
> However, there is one thing still couldn't find a way - how to convert
> 2D mouse coordinates into OpenSG world coordinates. Pablo helped me
> understand it, but I couldn't implement it yet. I found there was one
> method which translate the world coordinates into screen coordinates
> in OpenSG (getWorldtoScreen). My questions is that there exists sort
> of getScreentoWorld function in OpenSG. If not, how can I convert
> mouse's x,y coordinates into world coordinates (x, y, z)?
>
> Thank you always!
>
> Jung
>
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