Camera-view position and how it relates to overall system performance is a function of many considerations. Object focal point and distance, camera elevation, direction of the camera lens, viewing angles, lighting and the end user's own perceptions are all critical factors in system design.
Whether the project is a small system with a few interior cameras or a larger system with both exterior and interior cameras, a number of factors should be considered in the placement of cameras and their fields of view.
End users have preconceived notions of what the video system will provide in terms of camera views and video output and, most importantly, what this means in terms of cost and what they are willing to pay. Most end users want the most coverage with the least expense. This is only natural. It is up to the contractor or the system designer to consider all of these variables and to configure a system that satisfies the user and the design parameters. Systems integrators need to look at the customer’s wants and the features, which the proposed system offers, and design the video system around the end user's expectations and his budget. The end user's expectations should be married to the physical realities of the property and the system design.
In the Zone
For interior camera views, the size of the room, the context of the subject, the angle at which the camera sees the subject and the intended view need to be considered. Is the camera looking toward an exterior door or window? If it is, an object to be viewed in front of the door or window can be washed out. Even the newest backlight-compensation cameras will have trouble defining a subject in certain harsh lighting conditions. It would be better to locate the camera where it will see the light source from the side. For example, if an end user wants to see the face of a person entering a room and if there is only one door, place the camera so that it will view the face when the person leaves the room.For optimum view angles, place cameras in room corners. Using a wide-angle lens, it may be possible to view the entire room, depending on room size and the camera’s optimum field of view. A camera placed in the center of a wall will limit the field of view and will most likely miss the corners adjacent to the camera’s position.
In small rooms, a low-profile dome will provide good coverage and will be located on the ceiling out of the way of meddlesome hands. In larger rooms, there may be a need for multiple cameras. By using a crossover-field-of-view technique in which each camera looks at, or near, the others, a maximum field of view can be obtained.
Exterior camera placements provide a separate set of problems for maximizing video coverage. Cameras are usually required to cover much bigger areas. There is the problem of selecting a focal point, which will provide the optimum camera view. Also, consider lighting. Is enough light available for minimum illumination during evening hours?
When faced with large exterior areas that require video coverage, determine the proper focal point of the camera. Once the focal point is established, a camera position can be selected and a lens can be chosen that will provide the correct image size. When providing video coverage of large areas, it is critical to establish what the camera will see. Example 1 shows a large car dealer’s lot. Using standard wide-angle lenses will enable the customer to see his entire lot with only a few cameras. Although using this technique may provide a panoramic view of the lot, it doesn’t provide adequate image clarity if you need to see something more than 40 feet from the camera. As illustrated in Example 2, more detail can be provided farther from the camera, but the wide scope of Example 1 is lost. If establishing the focal point near the outer reaches of the lot, Example 3 shows that a realistic image can be seen at a more distant point, but the ability to see the larger area is lost.
Consequently, the farther away from the camera the primary object or scene to be viewed is, the narrower the field of view. To view the entire lot as in Example 1 but with a more defined and narrower field of view would require a large number of cameras. This is usually not cost effective, and a design decision must be made. Although the end user will get the added benefit of the image clarity he needs, this larger number of cameras may be cost prohibitive. At this point, considering camera placements and focal points becomes a contractor/customer decision. Design alternatives such as viewing entrance and exit points, vehicular and customer flow patterns, building exits or geographical zones within the field of coverage may be considered. Such alternatives may provide flexibility to the original design scheme.
Lighting is a crucial consideration when determining the necessary number of cameras and where to place them. Most exterior video systems need to see while dark. Before establishing the final focal point, determine if there is adequate lighting at night to provide the images needed. It may be necessary to view images where enough light is available and to forgo views of other areas that don’t have enough lighting. One solution to lighting problems is to add infrared illuminators. Using black-and-white cameras with a properly chosen infrared illuminator will provide ample lighting to see clearly in the dead of night.
In Focus
Using the example of the car lot again, it may possible to use exterior poles for mounting cameras. This would add alternative perspectives to camera views and could provide particular zone coverage. It would also help to reduce the need for a longer lens to obtain the correct focal point. If the pole has or can be provided with a light source, all the better, as this would supply ample light for nighttime viewing. However, the benefits of using existing poles are often offset by the added cost of bringing in electric power, cable or a wireless connection.Many elements contribute to the design of a video system. Certainly the head-end equipment gets much of the attention in any video security system, and perhaps deservedly so. However, possibly the most primary concern of any video system is the careful placement of the cameras. Quality camera placements that keep an eye on the overall scope of the project, and also places the end user's expectations in the forefront is what makes a good video system cost effective and a quality management tool.
