A visibility conception can be optimally realised in the vehicle only if the eye positions of the driver with reference to the vehicle are known. Here, the eye ellipses serve the purpose of describing the eye positions.
The eye ellipse results out of a set of lines that envelop and thus isolate that area (ellipse). These lines are the ones that divide the measured eye positions into 5% and 95% of the area. So, in general, the proportion created by these lines is always P% and (100 - P)%.
The size and the inclination of the eye ellipse depend on the driver population, the seat adjustment range and the position of the eye ellipse i.e. the point of origin of the backrest inclination as well as the position of the SgRP. The eye ellipses are standardized in SAE J 941 A. The slide shows a schematic representation of the 95 % eye ellipse.