Describing and Evaluating the Truck Driver's Viewing Environment
This SAE Recommended Practice establishes three alternate methods for describing and evaluating the truck driver's viewing environment: the Target Evaluation, the Polar Plot and the Horizontal Planar Projection. The Target Evaluation describes the field of view volume around a vehicle, allowing for ray projections, or other geometrically accurate simulations, that demonstrate areas visible or non-visible to the driver. The Target Evaluation method may also be conducted manually, with appropriate physical layouts, in lieu of CAD methods. The Polar Plot presents the entire available field of view in an angular format, onto which items of interest may be plotted, whereas the Horizontal Planar Projection presents the field of view at a given elevation chosen for evaluation.
These methods are based on the Three Dimensional Reference System described in SAE J182a. This document relates to the driver's exterior visibility environment and was developed for the heavy truck industry (Class B vehicles, class 6, 7, 8 vehicles) although the projection principles presented in this document can be applied to any class of motor vehicles.
This document is intended to complement SAE J1050a and provides a visual format that can describe the driver's entire viewing environment. This environment can then be analyzed to determine what the driver is capable of seeing. It should be noted that one of the most important factors affecting the driver's field of view and the ability to make valid vehicle/design comparisons is the location of the driver's eyepoint. SAE J941 defines the Eyellipse which forms the basis for eyepoints chosen as the origin for Polar Plots and Horizontal Planar Projections. The Target Evaluation, Horizontal Planar Projection and Polar Plot create monocular evaluations. Projections/plots of multiple eyepoints must be overlaid to create binocular or ambinocular evaluations.
Analytical methods for creating Target Evaluations, Polar Plots and Horizontal Planar Projections for direct and indirect vision (planar and spherical convex mirrors) are presented. Note that it is possible to create plots and projections for other mirror surfaces and vision devices if the equations for determining reflection points are provided.
The 1995 version of this SAE Recommended Practice presented only two methods of evaluation: the Polar Plot and the Horizontal Planar Projection. Each of these methods is insufficient to adequately describe both direct and indirect fields of view around the entirety of the vehicle. However, the document referenced additional “experimental and graphical methods” that were defined at the time as beyond the scope of the document. This release is intended not to replace methods originally presented, and rather adds the preferred Target Evaluation, which allows for utilization of available tools that complete the original purpose of this Recommended Practice.
The Target Evaluation Method may be utilized for alternative vision systems as well (i.e., cameras and monitors), but additional work is necessary to specify system requirements that appropriately consider valid image representation (clarity, acuity, distortion, size, etc.).
A minimum mirror radius of 300 mm for a spherical convex mirror is recommended based on a consensus of the committee. Appendix D describes the rational for this limit which is derived from considerations of visual acuity and typical vehicle layout.
In establishing a Target Evaluation Procedure, care was taken to ensure that the evaluation could be conducted in a simulated environment with appropriate CAD utilization, or equivalently with manual methods. This procedure details target cylinders and spacing, which were selected to be similar to the concept established in the Federal Regulation FMVSS 111, as required for school buses, with notable improvements.
Within the Target Evaluation Method, it is acknowledged that the extrapolation of the solid angles to form a vision cone, are not fully detailed in this Procedure with consideration of ergonomic limitations (i.e., head and eye movement). These limitations should be considered, but as with the previous 1995 version, are beyond the scope of this document.
It is recognized that the Target Evaluation Procedure counts the cylinder targets on the boundary between zones twice but it was judged by the Task Force to be preferable over a more complicated procedure that attempted to resolve the double count. This resolution of boundary target cylinders also allows each zone to be assessed independently, as well as in summary, to achieve a field of view volume evaluation.
The Target Evaluation Procedure requires a setup with the mirrors in the nominal adjustment position. The Task Force intended to require that both the top and bottom corners of the extremities of the vehicle would be visible, but it was determined that in most situations these extremities could not be viewed simultaneously without adjusting the mirror surface from nominal. Therefore, the bottom extremities of the vehicle were chosen as required view points.