The camera should be able to see the plate with a few millimetres of the plate.
The image below shows the different characteristics of the images presented with different focal lengths within different distances. Summary: in a certain focal length, the farther the distance is taken, the smaller the subject scene is; Within a certain distance, the longer the focal length is, the narrower the visual Angle of the photograph, the clearer the subject matter.
See the detailed rules = 2 * X physical features = X behavior = X / 2 (lens and measured distance is X meters, focal length is mm)
POMEAS provides monitoring of another lens focal length estimation, this only applies to more than 4 mm lens. For example, if the focal length of the lens (unit mm) is expressed in X, then the detail needs 2 * X, the outline is X, and the activity of the main body is X / 2. If you select a distance of 10 meters from the distance monitoring camera, you can see that the main activity selects the 5mm lens, the outline needs to be about 10mm, and the details need 20mm lens
