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The use of a 3:1 ratio of vertical to horizontal exaggeration in CGI for digitized terrain data was investigated by the method of constant stimuli. Hard copy line drawings of CGI was compared with actual terrain. The overall ratio of exaggeration picked by four observers was 1.25:1 to 1.50:1. The range of exaggerations for different viewing distances was 1:1 to 1.75:1. The data showed evidence of visual constancy matching and an anchoring effect.

Signal detection theory has been used extensively to determine the abilities of people. It has another use than can provide a partial solution to computer simulation and system developers who must model human performance. The problem with modeling human performance, at present, is that psychology has only provided models that have limited applicability to narrow performance domains. The receiver operating characteristic (ROC) curve can be used to model human behavior in such a way that the system developer can model the skill and motivation level of human performance. Furthermore, the developer can specify the errors and correct response that a person will make at a given skill and motivational level. This ability to model human performance should provide a means to generate design constraints for computer simulations and systems in which the human is an integral part.