When determining camera placement during installation, many factors must be taken into account. As mentioned in Camera Selection, the surveillance objectives decide what type of camera should be used, as well as how the camera should be placed.
Acquiring a useful image involves much more than simply pointing the camera at an object. Lighting, angle, reflections, dead zones, and the zoom factor for PTZ cameras are things to consider. Avoiding backlight and minimizing reflections are other factors that should be addressed. In some environments, in order to solve challenging scene problems, it’s easier to change the environment itself.
Camera placement is also an important factor in deterring vandalism. By placing a camera out of reach on high walls or in the ceiling, many spur-of-the-moment attacks can be prevented. The downside may be the angle of view, which can be compensated for to some extent by selecting a different lens.
The purpose of each camera should be clearly specified. If the aim is to get an overview of an area to be able to track the movement of people or objects, make sure that a camera suitable for the task is placed in a position that achieves the objective.
If the intention is to be able to identify a person or object, the camera must be positioned or focused in a way that will capture the level of detail needed for identification purposes. Local police authorities may also be able to provide guidelines on how best to position a camera.
The fastest way to find out what focal length lens is required for a desired field of view is to use a rotating lens calculator or an online lens calculator. Both of these are available from Axis at: Lens calculators
The size of a network camera’s image sensor, typically 1/4 in, 1/3 in, ½ in and 2/3 in, must also be used in the calculation. The drawback of using a lens calculator is that it does not take into account any possible geometrical distortion of a lens.
To calculate the distance, use Pythagorean Theorem: a² + b² = c²
One camera will provide an overall view of the scene, but will probably not provide enough details for identifying people in the area. If this is one of the surveillance goals, then an additional camera needs to be included in the design (see Figure 11). Identification is now possible when a person enters a large area. The information about where and how many people are in the room can still be objectively obtained using an additional wide angle camera.
For successful camera placement, light considerations are crucial. It is normally easy and cost-effective to add bright lamps in both indoor and outdoor situations to provide the necessary light conditions for capturing good images.
When mounting cameras outdoors, it is important to consider how the sunlight will change during the day. It is also important to avoid direct sunlight, as it will “blind” the camera and can reduce the performance of the image sensor. If possible, position the camera with the sun shining from behind the camera.
The problem with backlight typically occurs when attempting to capture an object in front of a window. To avoid this problem, change the environment by repositioning the camera, or use curtains or plants or close blinds if possible. A carpet can also be used to minimize reflection in a situation like this, and reduce the amount of backlighting. If it is not possible to reposition the camera, add frontal lighting. Cameras with support for wide dynamic range are better at handling a backlight scenario.
When mounting cameras outdoors, it is important to consider how the sunlight will change during the day. During part of the day (sunset), the crossed-out camera in Figure 13 would be looking in the direction of the sun.
If the exterior of a building is to be monitored, the location can be more or less affected by direct sunlight. Place the camera where sunlight has minimum impact.
The different ranges/zones of a camera are depicted in Figure XX. The line closest to the camera is where the maximum height is detectable. The yellow line illustrates the minimum required detectable height. The detection zone is in between these lines. These factors need to be addressed at the time of installation to ensure proper camera coverage.
Field of view must be checked both horizontally and vertically. Often the planning is based on floor plans which give you only a top view of the area. The side view must also be considered to ensure desired coverage.
When placing cameras at doors or in lobby environments, care should be taken to avoid a high angle of view. As seen in the images, the larger the angle to the object, the more difficult facial features are to recognize. As seen, 10-15° would give the best view for facial identification. On the other hand, placing a camera higher up puts it out of reach for vandals. It all goes back to the surveillance goals – is identification necessary?
© 2015 Axis Communications AB. All rights reserved