Hi David, The osgUtil::IntersectVisitor works in floats so will produce precision problems when working on geocentric databases. The easist solution is to start the intersect traversal below the MatrixTransfrom of the tile you;re wanting to insert your object, as its the MatrixTransform that create the large offset and introduces the numberical precision issues.
Robert. On 6/2/06, David Lascombe <[EMAIL PROTECTED]> wrote:
Hi everybody and thanks to those who answered my concerns about setting my scene in greyscale. I was wondering if I should use shaders as well to compute intersection points... Actually my problem is that I want to put a tank or land entity at altitude zero (on the ground). There was a NPS Tutorial about this so I have inspired myself a lot from it and it works fine when I use a ground database in a local coordinate system. However, as soon as I switch to Earth-Centered coordinates (using a 3D model like bluemarble, or any earth-centered database), I have some real offset on the computed intersection point and the visible ground altitude. My tank's 3D model has no offset and here's my way of doing this : I create a segment between the entity's earth-centered position and earth's center (0,0,0). Then I use the Intersect Visitor to get the Hit list containing the intersection points in world coordinates. At first I only took the first intersection of the list (hitList.front()), assuming there was only one, but I even checked if there were other intersection and compared them to get the nearest to the earth center. Depending on the database the tank is a couple of dozens of meters above ground or deep underground. I even thought it might be bound to earth's shape being ellipsoidal, so I tested at the equator, but the very same thing happens. Should I redefine the Intersect Visitor? Where does this offset comes from anyway? If anyone had experienced similar issues in computing intersection points I would be glad to have some advice. Thanks in advance, David _______________________________________________ osg-users mailing list [email protected] http://openscenegraph.net/mailman/listinfo/osg-users http://www.openscenegraph.org/
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