Landscape and curvature of the Earth


I’m writing an application that simulates the behavior of radio waves. Therefore it’s necessary to take into account the curvature of the Earth’s surface.
I’m using a real height map (srtm) and L3DT software to prepare raw data for import into ue4.
I don’t need to display the entire Earth, only a small part (about 1000x1000 real km).
Which are the ways (or tools/software) to deform the landscape according to the curvature of the Earth?