Document ID: chunk:federal_register_of_legislation:F2024C00148:reg:1:p27
Version: federal_register_of_legislation:F2024C00148
Segment Type: reg
Provision Reference: reg 1 (pt 27/34)
Character Range: 209155–212275

method, but involves equilateral triangular test patterns. The Triangle Orientation Discrimination method is described in detail by Bijl & Valeton (1999), who provide practical guidelines on how to perform a TOD measurement. In the method, triangular test patterns (see Figure 1) are viewed through the viewing system under test. Each triangle can have one out of four possible orientations (apex up, left, right or down) and the observer indicates/guesses for each triangle its orientation. When this procedure is repeated for many (randomly oriented) triangles of different sizes the fraction of correct responses can be plotted (see Figure 2), and increases with test pattern size. The threshold is defined as the point at which the fraction correct crosses the 0.75 level and can be obtained by fitting a smooth function through the data (see Bijl & Valeton, 1999). Critical perception is reached when the critical object diameter equals two times the width of the triangle at threshold size. The smallest discernable detail (ωc) is equal to 0.25 times the width of the triangle at threshold size. This means that, from the threshold triangle width w [m] and the distance between test pattern and the camera D [m] the smallest discernable detail ωc [arcmin] is calculated as follows:

       Figure 1
       Triangular test patterns used in the Triangle Orientation Discrimination (TOD) method

       Figure 2
       Typical relationship between the size of the triangle and the fraction of correct responses

              1.2.  Determination of the critical viewing distance of the monitor

               For a monitor having certain dimensions and properties, the distance to the monitor can be calculated within which the detection distance is dependent only on the performances of the camera. The critical viewing distance rmcrit is defined as the distance at which the smallest discernable detail displayed on the monitor spans 1 arcmin measured from the eye (the acuity threshold of a standard observer).

              Where:
              rmcrit : critical viewing distance of the monitor [m]

              δ : size of the smallest discernable detail on the monitor [m]

              1.3. Determination of the detection distance

              1.3.1. Maximum detection distance within the critical viewing distance where, due to the installation, the distance eye-monitor is less than the critical viewing distance, the maximum attainable detection distance is defined as:

               Where:

                  rdclose: detection distance [m]

                  D0 :  diameter of the critical object [m] according to paragraph 2.1.2.6. of this Regulation; for the calculation of rdclose for Class V and VI devices, a representative value of 0.30 m shall be used

               f:  threshold increasing factor, which is equal to 8

               ωc:  smallest discernable detail [arcmin]

              1.3.2. Detection distance greater than the critical viewing distance. Where, due to the installation, the distance eye-monitor is more than the critical viewing distance, the maximum obtainable