On Dec 13, 2007 9:03 PM, etrek <[EMAIL PROTECTED]> wrote: > In OpenGL Y axis is up ( world and view ). > In DirectX Y axis is up ( world and view ).
They define Y up in *eye* coordinates. The modelview matrices put you into eye coordinates, of which must be standardised. They don't actually say anything about the coordinates of the world, this is what the inverse of the view transform defines. > The two most popular graphics API's consider Y axis as up. So do most > Graphics texts like Foley et al. > > OSG uses OpenGL as its graphics API, so why not use the same coord system? > > Just curious as to the reasoning behind this design decision. The OSG is built around the concept of worlds coordinates rather than eye coordinates - its about creating virtual worlds, which in turn have a counter part in the real world and in the real-world (disciplines beyond computer graphics) one generally to X going east, Y going north, Z going up. Z is most commonly up and refers to height. Not surprisingly the vis-sim market grew up around this too rather than getting fixated on eye coordinates being akin world coordinates... For me one of the key things in grasping real-time computer graphics is to get a handle on the ideal of different coordinate frames - world coordinate and eye coordinates being two different coordinate frames used for two different things. Robert. _______________________________________________ osg-users mailing list [email protected] http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
