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.com>wrote: > 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 >
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