That's actually how the displacement of the intersection is done here - marching in the range between spheres. Bisection, however, wont work at shallow angles.
@rcarmo Yes, bumps are enhanced, to make the surface more dramatic. This scale is a parameter in the notebook, it can be set to the realistic 1.15% of the mean radius.
On another forum, someone pointed out that the Lambertian shading makes the Moon surface too smooth. So the diffuse material roughness will come in the next PlotOptiX release, in a few days. :)
PlotOptiX requires NVIDIA GPU. I used GTX1060/6GB on a laptop for most of the work. Tested also on a desktop RTX1070/8GB, much better fps, of course. Video is done on RTX. In Google Cloud, on V100, runs even faster, but GUI is more convenient on local machine.
Ray-tracing is done in a Python notebook. Data originates from NASA public resources. I searched for the highest resolution data to make the Moon almost touchable. So it is made of 118m elevetion model and 480m surface color. There is also 59m elevation model, but this 22GB does not really fit into my laptop's GPU.
Code can run on GCP instance. Laptop/desktop is more convenient, though.