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Line of sight and angle of view

One of the most critical design issues in any control room design featuring CCTV should be the line of sight and angle of view of monitors to operators. The monitors and their angle of view effectively determines the usability of the interface for the operator in order to accomplish surveillance objectives. Yet despite the importance of these, they are often neglected in the technical installation of the control room.

There are a number of issues relating to how the angle of view affects the quality of surveillance. I have divided these up into a few different areas to facilitate looking at the related issues more easily.

Physical issues

Physical issues relate to where and how monitor screens are placed on desks, consoles or walls within the control room. One of the most common issues is placing monitors too high so operators either have to tilt their heads uncomfortably upwards, or lean back in their chairs to avoid muscle strain. Leaning back creates the conditions for people to become too relaxed and together with tiredness, leads to people dozing or ‘tuning out’. The other alternative for operators is just to disregard the monitors positioned too high and they cease to be a source of information.

Besides the actual positioning, the angle at which monitors are attached is also an issue. One can often find monitors placed high up and facing directly away from the wall – this creates a double problem as will be discussed in the section on LCD screens. Consoles that are inclined slightly forward, or monitors fixed to allow a tilting downwards allow an operator to have a more direct view of the scene displayed on screen and facilitate natural viewing. One can even find that monitors on desks would benefit from slight tilting or height adjustments up or down to make for more ergonomic viewing. The problem with tilting monitors appropriately is further complicated by the fact that the mounting fittings are not standardised and just the process of attaching them to the console or wall is a complicated process that allows little flexibility or ongoing adjustment.

Where desktop monitors are used in conjunction with wall mounted monitors, a simple aspect of ensuring that you can see past the desktop monitor clearly is often neglected. Operators are looking around or even leaning to the side of their control screens in order to see what kind of effect changes or adjustments may have on the monitor wall. A further part of the physical environment that is a common issue is the chairs upon which the operators sit.

Good control room chairs are difficult to come by and the standard issues often have hydraulic functions that fail fairly quickly. At this point with no hydraulic pressure, operators are sitting in the lowest position relative to the ground compared to what is expected, and viewing angles of the wall and desk monitors often change as a result. Distance is also a complicating factor. While one may think of monitors being too far away, the increasing use of big 40-inch and large TV type screens has suddenly brought things in too close, and one almost has to physically lean back in order to view some areas of the screen, with visual discomfort and eye strain an additional possible outcome.

The screens themselves

LCD/LED and plasma screens have their own limitations built in with their possible angles of view. Side views and those from the top and bottom reach points where the quality and contrasts of image deteriorate so much that it becomes difficult to see what is on the screen properly. Not only this, but the colour range displayed can change as the viewing angle becomes more extreme.

When mounting such displays, this needs to be checked from typical seating and standing positions. In one control room I visited recently, as soon as one sat down in the seat, a number of monitors mounted high on a console became unviewable. Yet operators had not commented on it and a number of screen views were being disregarded on a constant basis over a period of a couple of years because of the viewing angle.

As camera viewing light conditions change, it also presents potential problems for monitors. The quality of lighting can change as it gets darker, and this can affect the colour intensity and the display contrast on screen. Even on my notebook, I find that darker images create more difficulty in viewing as soon as one changes the viewing angle from directly in front of the screen. In situations where CCTV is viewing, light intensity changes are a common issue beside the daily shift from light into darkness.

Lighting

Lighting reflections have one of the most potential disruptive influences on screen displays. This is especially the case with some monitors which have a more reflective surface. Direct lighting and fluorescent lighting are also the primary problems in that respect and wherever possible, indirect lighting should be used. While I am a fan of natural lighting, this needs to be channelled or provision needs to be made to adjust the effect of direct light, never mind sunlight in the control room.

Organisation

One ideally wants the best line of sight to the most important monitor displays. Yet all too often the monitors are mounted more in line with the fact that technicians want to place as many views as possible in one area. How the available workstation space is occupied by monitors should be based on a usability analysis and what the critical viewing needs are to do surveillance properly.

Another important part of this is that the control screens that are often used to manage camera selection and things like alarm screens should be in line of sight as much as possible. Where the operator has to look away repeatedly every time something is changed, he or she runs the risk of missing important surveillance information. Ironically, this is most likely to happen when an incident occurs and the operator has to look away in order to make selections or adjustments to screen or to obtain information, resulting in key aspects of incidents being missed. The line of sight and the angle of view issues also relates to use of communications equipment, which should be positioned so operators can maintain a clear view of the CCTV monitors while handling an incident. Where supervisors are also involved in monitoring what is going on, line of sight from the supervisor workstation is also an important element to bear in mind.

It amazed me at one stage where I sat down with a client and did a mock up on the proposed CCTV workstations to test line of sight and viewing angles, that it was the first time that the client who was a major national installation company had even done such a thing. Line of sight and angle of view issues are one of the most common problems in control rooms, yet they are the simplest to prevent and the most common sense one to get right. There is no need for expert advice for the most part – simply sit in a control room chair at the workstation and see if the setup works for you. Ensuring the design works well in the beginning will solve a lot of problems later.

Dr Craig Donald is a human factors specialist in security and CCTV. He is a director of Leaderware which provides instruments for the selection of CCTV operators, X-ray screeners and other security personnel in major operations around the world. He also runs CCTV Surveillance Skills and Body Language, and Advanced Surveillance Body Language courses for CCTV operators, supervisors and managers internationally, and consults on CCTV management. He can be contacted on +27 (0)11 787 7811 or [email protected]

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