Looking for 3D graphics engine

[Spitfire]

I would start here, then narow it down to license/language etc you're interested and research more on each engine's website.

Few years back I was using Ogre 3D ( for games not physical simulations ) and I found it not that hard to learn.

If you have some money to spend on the license then It may be worth looking at Unity 3D or something similar.

[d_stranz]

You should also look into Kitware's Visualization Toolkit (VTK). Written for the US Sandia National Laboratory, and although the Creative Commons license does not permit derivatives of the work, it can be freely used in any type of project. It is complex and comprehensive enough that you probably wouldn't want to modify it anyway.

There are bindings and interfaces to Qt, Python, and a number of other languages. The learning curve is sort of steep, though. The API is at least as extensive as Qt in the number of objects and methods. Like Qt, it has a parent-child ownership hierarchy among objects, but unlike Qt, it uses a reference-counted "object factory" model to create and destroy instances.