CCTV Cameras - Fields of View and Floor Area Coverage
Fields of view required by CCTV system operators are described by five (5)categories of view as Monitor and Control. Detect, Observe, Recognise and Identify. These terms are defined as follows:
To simplify the situation and provide guidance to a system specified, five general observation categories have been defined, which are based on the relative size that a person appears on screen (see below). As part of the installation process and development, the user will be asked to decide which of these four categories best reflects the type of activity being observed. The CCTV installer will then be able to fit a suitable camera to meet the requirement.
Monitor and Control – A figure occupies at least 5% of the screen height and the scene portrayed is not unduly cluttered. From this level of detail an observer should be able to monitor the number, direction and speed of movement of people across a wide area, providing their presence is known to him; i.e. they do not have to be searched for.
Detect – When reviewing images, investigators are able to ascertain with a high degree of certainty whether or not a person is present, and are able to track their movements throughout the area covered by the camera for continuity purposes. Detecting quality images also gives a good overview for crowd monitoring (when viewing live images).
Observe – Provides a sufficiently wide field of view to enable the observation of activity around an incident perhaps involving several individuals, whilst providing sufficient basic detail of the individuals concerned, (e.g. colour and style of clothes), and the activities taking place.
Recognise – When reviewing images investigators can say with a high degree of certainty whether or not an individual shown is the same as someone that they have seen before. This is used to recognise the suspect that they have in custody or the person that they have an identification quality picture of from another source or location. These images are also used to ascertain detail of an activity taking place.
Identify – Picture quality and detail should be sufficient to enable the identity of an individual to be established beyond reasonable doubt to support a prosecution.
The Monitor or Detect categories may be suitable for covering a wide area such as a car park. The Observe category is useful in areas where it is necessary to monitor a group of individuals such as outside nightclubs and pubs, or in town centres, as it provides reasonable detail of the subject whilst simultaneously providing some context to their activity by monitoring the area around them. The Recognise or Identify categories would be used for the cameras providing close-up images at the entry and exit points. In scenarios where the purpose of the camera is primarily access control and identity verification, a figure much greater than the 100% Identify setting may be required.
Consider which of the five ‘levels of detail’ described above is most appropriate to your requirement.
You may wish to:
• Monitor a large area
• Detect individuals approaching a building
• Observe the actions of a group
• Recognise known individuals at an entrance
• Obtain images that would enable you (or the police) to identify an unfamiliar individual
A typical fixed camera can be specified to cover a narrow field of view with a high level of detail (for recognition / identification purposes), or a wide field of view at a lower level of detail (for monitoring / detection), but generally not both. Thus it is important to consider carefully which of these requirements is the more appropriate for each location.
Camera coverage and image quality are of paramount importance if images are to be successful in identifying crowd movement or individuals and proving their actions at a crime scene, beyond reasonable doubt. Poor camera coverage or image quality will produce CCTV pictures of little or no operational or evidential value.
It is acknowledged that the physical make-up of businesses and offices can vary greatly and it is recommended that individual surveys are carried out for each location to ensure that the CCTV system covers the key areas.
Key areas where special consideration should be given to the positioning of cameras are Pinch Points, Cash Tills, Controlled Areas, ATM, ticket machines and telephones. Cameras recording pinch points such as doorways and entrances should be focused close in on the area, providing an identification quality picture in both directions. This type of view should have a higher frame rate in order to capture images of individuals moving quickly through the area.
Scene views should be determined before the cameras are installed; it is recommended that pictures of the required scene view are provided in the CCTV installation documentation and used as the benchmark for final acceptance.
Wherever possible, cameras should be positioned between three and three and a half metres high on a rigid structure to avoid vandalism, damage or being knocked out of alignment.
Column mounted cameras should be protected with an anti climb guard fixed below the camera on the column. Columns are available in a variety of designs, heights and styles.
Further CCTV Technical Information and Guidance