I think you quoted the "why" in your own email -- Z-up corresponds to the predominant usage in the vis-sim community. OpenGL doesn't enforce an up vector policy. Object coordinates are arbitrary and up to the application. If you don't set the modelview matrix, then object coordinates are equivalent to eye coordinates, and OpenGL defines eye coordinates as Y-up. However, I know of no applications that use the default (identity) modelview matrix -- every app sets it, and every app therefore determines their own up vector. Most OpenGL-based vis-sim apps set the modelview so that Z is up. OSG provides this same orientation by default. Note that, just like in OpenGL, you can set your own modelview matrix in OSG, and therefore set your own up vector. Does that answer your question? Paul Martz Skew Matrix Software LLC http://www.skew-matrix.com <http://www.skew-matrix.com/> 303 859 9466
_____ From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of etrek Sent: Thursday, December 13, 2007 2:03 PM To: [email protected] Subject: [osg-users] What was reasoning behind OSG Z up axis Hello, I looked at the archives and found someone else posted question about Z axis. Here is link: http://lists.openscenegraph.org/htdig.cgi/osg-users-openscenegraph.org/2007- July/000209.html I question this part of the answer: "The OSG follows the majority of the vis-sim industry in having +ve Z up, +ve Y north and +ve X east." In OpenGL Y axis is up ( world and view ). In DirectX Y axis is up ( world and view ). 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. NOTE: How to transform the axes is explained here: http://lists.openscenegraph.org/htdig.cgi/osg-users-openscenegraph.org/2007- August/001059.html . So I know how to change it programmatically if I wanted to. Thanks, Eday <http://lists.openscenegraph.org/htdig.cgi/osg-users-openscenegraph.org/2007 -August/001059.html>
_______________________________________________ osg-users mailing list [email protected] http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
