Document ID: chunk:federal_register_of_legislation:F2023L01006:reg:780:p4
Version: federal_register_of_legislation:F2023L01006
Segment Type: reg
Provision Reference: reg 780 (pt 4/8)
Character Range: 86336–89175

is 635 mm vertically above the H point (H) and 96 mm aft of the H point.

              (b) Locate the head/neck joint centre (J) illustrated in Figure C so that it is 100 mm rearward of Mf and 588 mm vertically above the H point. In the case of the head/neck joint centre (J) is not compatible for the vehicle seat configuration, adjust the driver's seat to the midpoint of the longitudinal adjustment range. If the seat cannot be adjusted to the midpoint of the longitudinal adjustment range, the closest adjustment position to the rear of the midpoint shall be used.

              (c) Draw an imaginary horizontal line between Mf and a point vertically above J, defined as J2.

              (d) Rotate the imaginary line about J2 in the direction of the rear-view image until the straight-line distance between Mf and the centre of the display used to present the rear-view image required in this standard reaches the shortest possible value.

              (e) Define this new, rotated location of Mf to be Mr (eye midpoint rotated).

         3.1. Measurement procedure.
              (a) Locate a 35 mm or larger format still camera, video camera, or digital equivalent such that the centre of the camera's image plane is located at Mr and the camera lens is directed at the centre of the display's rear-view image.

              (b) Affix a ruler at the base of the rear-view image in an orientation perpendicular with a test object cylinder centreline. If the vehicle head restraints obstruct the camera's view of the display, they may be adjusted or removed.

              (c) Photograph the image of the visual display with the ruler included in the frame and the rear-view image displayed.

         3.2. Extract photographic data.
              (a) Using the photograph, measure the apparent length, of a 50 mm delineated section of the in-photo ruler, along the ruler's edge, closest to the rear-view image and at a point near the horizontal centre of the rear-view image.

              (b) Using the photograph, measure the horizontal width of the upper portion of each of the three test objects located at positions G, H, and I in Figure B.

              (c) Define the measured horizontal widths of the three test objects as dG, dH, and dI.

         3.3. Obtain scaling factor.
         Using the apparent length of the 50 mm portion of the ruler as it appears in the photograph, divide this apparent length by 50 mm to obtain a scaling factor. Define this scaling factor as scale.
         3.4. Determine viewing distance.
         Determine the actual distance from the rotated eye midpoint location (Mr) to the centre of the rear-view image. Define this viewing distance as aeye.
         3.5. Calculate visual angle subtended by test objects.
         Use the following equation to calculate the subtended visual