[osg-users] replace tile with my own Node in VPB generated QuadTree

Sebastian Messerschmidt sebastian.messerschmidt at gmx.de
Sat Dec 3 08:04:12 PST 2016

Hi Nick,
> Hi Robert, Community,
> I am hacking the VPB process again :-).
> The story is this: I transform tiles back from ECEF to local, do 
> something with the Geometry and I want to replace the tile with my own 
> Node. Spent already hours reading and trying to understand the 
> SceneGraph with all this transforms, and I am failing.

> Any words of how these tiles in the QuadTree are represented? I mean 
> the tree and the transforms, I know the facts that they are coming 
> from TerrainTiles with proper Locators, but after when the 
> GeometryTechnique is applied.
I worked it out some years ago, where I needed to capture the 
transformations for a query-representation. Basically you will have a 
height field-layer inside the terrain-tile, which describes itself via a 
Locator and the height-values in a normalized coordinate frame. IIRC the 
complete ECEF-Transform is captured inside the locator. It simply 
assumes the height-field as being centered around the geographic 
position when creating the world-geometry.
Some snippet to retrieve the world-coordinates of the terrain-tile's center:
         osgTerrain::TerrainTile& terrain_tile = 
         osgTerrain::HeightFieldLayer* hf_layer= 
         osgTerrain::Locator* locator = terrain_tile.getLocator();
         osg::EllipsoidModel* es = locator->getEllipsoidModel();

         //compute center transform
         osg::Vec3d center_model;
         tile ->convertLocalToModel(osg::Vec3d(0.5,0.5,0.0), center_model);

I'm not quite sure which coordinate frame is used in the quadtree 
itself, but it should be easy enough to put some subgraph to an osgt to 

> Thanks so much for any word on this. It is the last bump in my current dev
> Cheers,
> Nick
> -- 
> trajce nikolov nick
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