Robert,
I think I get your point, but just to be sure.
Dealing with double precision data involves:
- the native data (double precision), stored in an osg::Vec3dArray,
attached to an osg::Geometry object,
- the data reduced to floats, stored in the _vertexArray member
variable of the osg::Geometry object for rendering,
- attaching the osg::Geode to an osg::MatrixTransform (double
precision), so that both the double precision data in the
osg::Vec3dArray and the simple precision data in
osg::Geometry::_vertexArray are affected by the same transformation
matrix.
Did I understand correctly?
Émeric
2014-10-30 18:35 GMT+01:00 Émeric MASCHINO <[email protected]>:
> Hi Robert,
>
>> For instance for GIS whole world databases the usual way to manage things is
>> to load the data in doubles then transform to a local origin and reduce any
>> vertex data from doubles to floats in the process and store this data in
>> straight osg::Vec3Array in an osg::Geometry. You then place the object in
>> the correct world space by decorating the subgraph with a Transform
>> (typically a MatrixTransform) that places the local origin in it's correct
>> world position and orientation.
>
> So data are duplicated? There's the original dataset in double
> precision and a transformed one in single precision?
>
>> If you look at osgEarth and
>> VirtualPlanetBuilder this is how they manage whole earth databases,
>> maintaining floats where OpenGL hardware requires it, but using double
>> MatrixTransforms and the use of double ModelView Matrices in the OSG cull
>> traversal that ensures maintenance of precision as long as possible before
>> one finally has to copy the data to OpenGL.
>
> Thanks for the pointer.
>
> Unfortunately, osgEarth is such a huge beast to reverse-engineer! And
> their Coordinates Systems git page [1] isn't that much informative
> about the implemented architecture in this regard.
>
> I was wondering, since both the FBX/DAE plugin is able to handle
> double precision data, isn't there a -maybe- similar mechanism in
> straight OSG that allows for rendering a FBX/DAE mesh? Or is the
> double to float reduction internally handled by the plugin?
>
> Émeric
>
> [1]
> https://github.com/gwaldron/osgearth/blob/master/docs/source/developer/coordinate_systems.rst
_______________________________________________
osg-users mailing list
[email protected]
http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
