Figure 1. K-L Expansion of Autocorrelation Functions of 
Terrain Elevations. Orthogonal base functions (solid line) 
and auto-regressive processes (dashed line, vertically 
translated). 
In the work by Forstner (1983), it was assumed that the 
terrain elevations can be expressed by a second order auto- 
regressive (AR) process. When examining the base functions 
q, and d5; it was found that they are very similar to the 
correlation functions of autoregressive (AR) processes. 
Although not formally proved in this study, the basic 
assumptions by Forstner seems to be justified. For 
7687 -