Author here. Rayshader is an R package for mapping and 3D data visualization, and I've been working on this feature for a while now. Here are links to previous posts I've made on HN about the package:

Show HN: A raytracer to shade, plot, and 3D print topographic maps in R, part 4 http://www.tylermw.com/3d-printing-rayshader/

Show HN: A raytracer to shade and visualize topographic maps in R, part 3 http://www.tylermw.com/3d-maps-with-rayshader/

Show HN: A raytracer to shade topographic maps in R, Part 2 http://www.tylermw.com/making-beautiful-maps/

Show HN: A raytracer to shade topographic maps in R http://tylermw.com/throwing-shade/

Great work Tyler. Been waiting for it quite sometime. Just wanted to know how computational heavy it becomes rather than a normal ggplot?

Not that computationally heavy--usually takes under a minute to draw all the polygons and render the shadow map.