What DORI is
DORI are standard levels of detail: detection (you can see someone is there), observation (actions are visible), recognition (you can recognise a known person) and identification (a face can be reliably identified). They depend on how many pixels fall on one metre of the scene.
Wide or narrow lens
A 2.8 mm lens gives a wide view, but details are visible only up close. 6–12 mm gives a narrow frame, but faces and plates are readable further away. Entrances usually get a wide lens; gates and distant areas a longer or varifocal lens.