Definition and measurement of character dimension of fisheye camera module

From the specified point of view, all character dimensions are measured with angle values as the opposite angle of the feature (for example, height or width).

The angular values in radians are derived from linear values as follows:

αR=x/d

As follows:

α R is the angular dimension in radians;

X is the linear dimension of the character (e.g. height or width) projected on a plane perpendicular to the viewing direction;

D is the viewing distance from the posterior centroid of the monocular ellipse.

Both X and D should be expressed in uniform units, such as millimeters.

The angular dimension  a in arc minutes (1arcmin  1 ° / 60) is the dimension in radians as follows:

（A.2）

In actual use, formula (A.2) can be written as follows:

（A.3）

The character size shall be as defined in Figure a.1, using the characters "H" and "a". If normal and bold fonts are available, the character size is taken from the normal font.