Here a first trial to raycast perlin noise on the fly for achieving volumetric terrain rendering. In the demo, a 128^3 sized random volume data is used as a base for the scenes on the screenshots above.
By optimizing the empty-space skipping, it is possible to raycast reasonably large outdoor scenes at interactive framerates (20-40 fps) on a Nvidia GTX 260 GPU. The advantage of this kind of landscapes is, that they are extremely easy to handle and also that they are very memory friendly ( its just 128^3 rgba voxels = 8 MB of data ). Also can the performance easily adjusted for older graphics cards depending on the empty-space skipping configuration.
The Demo can be downloaded here: Perlin_Noise_Raycasting.zip Controls are w,s,a,d.