> -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf > Of Robert Osfield > > The pole looks weird. Is there any way to fix it? > > Poles are little bit awkward to fix with the simple quad tree > approach used by the OSG (and many other whole whole > techniques.) We could certainly do more to try and alleviate > this problem by better sampling around the poles when > building the terrain. Anisotropic filtering can help at runtime. > > Robert.
The problem is that the projection is not even close to linear at the poles, meaning that the mipmapping hardware does the wrong thing, anisotropic filtering may help, but you'll still get the weirdness, it will just be reduced. This is a limitation in using lat/long style texture projections as it means the pole is represented by a line in texture space rather than a point. For the earth this is not normally a problem because few people go to the poles and they are usually covered in ice and snow ( so have a very dull and uniform appearance ). For other planetary bodies in the solar system, sometimes the poles are very interesting though. In the past I've has success using a Azimuthal Equidistant projection ( http://en.wikipedia.org/wiki/Azimuthal_equidistant_projection ) for each hemisphere to bypass this problem for rendering planetary bodies. The problem with this is that the projection becomes less linear the further away from the projection points ( east and west 'poles' in my case ). I also know that other people have had success with a polyhedron based projection. The simplest would be using a cubemap style projection. These have the advantage that they use a number of linear projections, so any distortion could be corrected by use of the 4th texture coordinate. Colin. _______________________________________________ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
