Huge 8 x 8 km landscape created with Gaea and then scaled up 16 x 16 rendering in real-time at UE4 with custom illumination changes to get better performance, 12ms on 970GTX, complete time of day cycle.
Clouds are just a custom plane solution with TAA material to simulate transparency at long ranges.
The landscape features an automatic foliage spawner, and per range textures quality at low cost.