Re: [osg-users] OSGEarth precision
Hi David, I haven't dived into the source code of osgEarth, but I do know that it utilises osgTerrain, and osgTerrain internally uses double to locate tiles in their geocentric position (the class that does this is the osgTerrain::Locator). When the geometry for rendering is generated on demand it's created with a local origin and then decorated with a MatrixTransform that places the tile into it's final position. Since the OSG defaults to use double Matrix for MatrixTransform and doubles for all osg::Camera management, and the cull traversal accumulates the camera + transforms in the scene using doubles, it's possible to position the tiles very accurately and maintain precision for as long as possible before passing to OpenGL. When you are close to a tile, such as driving along it the relative translations of the camera and the tile's MatrixTransform largely cancel out with little numerical errors thank's to the use of doubles, so you get the best precision where you need it most, while far away tiles have larger translations left in them so the error is higher, but this is not an issue as vertices and divide by their distance during the transformation from object to clip space so the errors seen on screen remain subpixel so you don't see them. Thanks to this system it's possible to use pre-built VirtualPlanetBuilder or dynamically generated osgEarth databases in geocentric coords without complex additional coding, it just works out of the box. Whether you'd want to use a dynamically generated database from remote data for a simulator is a different matter, one would have to look closely at the latency and consistency of download and generating tiles. Robert. On Wed, Feb 4, 2009 at 7:10 AM, David Karlsson david.karls...@foi.se wrote: Hi, Is OSGEarth suitable to use, as a part of a terrain simulator, together with objects that needs to be positioned with about cm precision - or will I run into problems with precision? I found this page about how they handled it in NASA's World Wind: http://www.urbanrobots.com/Blogs/WW/2006/01/working-to-solution-in-precision.html How is this handled in OSGEarth? Thanks, David ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
Re: [osg-users] OSGEarth precision
David, I'll just chime in for the record to echo Robert's correct assessment -- osgEarth uses osgTerrain under the hood, and osgTerrain solves the precision issue by localizing each tile at each level of detail with a double-precision matrix. Glenn Waldron : Pelican Mapping : http://pelicanmapping.com : +1.703.652.4791 On Wed, Feb 4, 2009 at 4:14 AM, Robert Osfield robert.osfi...@gmail.comwrote: Hi David, I haven't dived into the source code of osgEarth, but I do know that it utilises osgTerrain, and osgTerrain internally uses double to locate tiles in their geocentric position (the class that does this is the osgTerrain::Locator). When the geometry for rendering is generated on demand it's created with a local origin and then decorated with a MatrixTransform that places the tile into it's final position. Since the OSG defaults to use double Matrix for MatrixTransform and doubles for all osg::Camera management, and the cull traversal accumulates the camera + transforms in the scene using doubles, it's possible to position the tiles very accurately and maintain precision for as long as possible before passing to OpenGL. When you are close to a tile, such as driving along it the relative translations of the camera and the tile's MatrixTransform largely cancel out with little numerical errors thank's to the use of doubles, so you get the best precision where you need it most, while far away tiles have larger translations left in them so the error is higher, but this is not an issue as vertices and divide by their distance during the transformation from object to clip space so the errors seen on screen remain subpixel so you don't see them. Thanks to this system it's possible to use pre-built VirtualPlanetBuilder or dynamically generated osgEarth databases in geocentric coords without complex additional coding, it just works out of the box. Whether you'd want to use a dynamically generated database from remote data for a simulator is a different matter, one would have to look closely at the latency and consistency of download and generating tiles. Robert. On Wed, Feb 4, 2009 at 7:10 AM, David Karlsson david.karls...@foi.se wrote: Hi, Is OSGEarth suitable to use, as a part of a terrain simulator, together with objects that needs to be positioned with about cm precision - or will I run into problems with precision? I found this page about how they handled it in NASA's World Wind: http://www.urbanrobots.com/Blogs/WW/2006/01/working-to-solution-in-precision.html How is this handled in OSGEarth? Thanks, David ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
[osg-users] OSGEarth precision
Hi, Is OSGEarth suitable to use, as a part of a terrain simulator, together with objects that needs to be positioned with about cm precision - or will I run into problems with precision? I found this page about how they handled it in NASA's World Wind: http://www.urbanrobots.com/Blogs/WW/2006/01/working-to-solution-in-precision.html How is this handled in OSGEarth? Thanks, David ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
