I played around with the Qt 3D frameworks a bit... so far it looks very promising. Below is a screenshot of the 'Surface Example' which makes use of the Q3DSurface component.

The 'Textured Surface Example' demonstrates how to overlay a map onto the terrain.

These examples should be a good starting point for developing the Synthetic Vision features. I'm not sure about the performance of these frameworks on single board computers. For embedded applications the 'Boot to Qt' stack will come in handy.