1. A method for high-performance terrain rendering via a topographical program executed by a computing device, the method comprising the steps of: obtaining elevation data; determining slope of a terrain surface; selecting a shading model to apply to the terrain surface based upon the slope of the terrain surface; storing an image dataset of surface normals as a polar-coordinate index to a shading look-up table stored in a memory of the computing device, the shading look-up table being loaded with shading percentages derived from the shading model, said shading percentages being computed off-line; adding a correction angle to a horizontal azimuth of the index when adjusting a lateral angle of an illumination source; and applying the index having the added correction angle to the shading lookup table.