Hi Frank, I think what you're seeing is the difference between a world coordinate system (where X is east, Y is north and Z is up) and OpenGl (where X is to the right, Y is up, and Z is coming out of the screen). What was Z up becomes Y (up the screen) and what was Y north becomes -Z (pointing away from the viewer). If you swap the Y and Z columns and multiply the new Z column with -1 you get your missing transformation.
> Frank Sullivan > Subject: [osg-users] [forum] Cameras View Matrix - I am perplexed > > Hello! > > I was wondering if someone could help explain the camera's > view matrix to me. The reason I ask is that, when I look at > it in the debugger, it is not at all what I expected it to be. > ... > matrix, which happens to be what my question is about. So > anyway, when I calculate the inverse of the camera's world > matrix, I get: > > -1 0 0 0 > 0 -1 0 0 > 0 0 1 0 > 0 500 -30 1 > > Multiplying my world-space vector [-1, 499, 31] by this > matrix yields [1, 1, 1], which is what I want. So, I'm > satisfied that this is correct. > > The problem is, when I actually call > osg::Camera::getViewMatrix() for this camera, what I get instead is: > > 1- 0 0 0 > 0 0 1 0 > 0 1 0 0 > 0 -30 -500 1 > ... > > So I was hoping someone could explain to me why this works > the way that it does, perhaps by pointing out an error in my > reasoning. I am trying to implement a shader that is similar > to shadow mapping, and it's not working, and this is the only > step along the way that isn't working as I expected it to. > > Thanks! > Frank Sullivan[/code] > _______________________________________________ osg-users mailing list [email protected] http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
