Site survey considerations
Before installing a surveillance system, we recommend you do a site survey and document it for future needs and upgrades.
There are many building blocks that make up a site survey, and this guide will help you identify them. One of the first things to define is the purpose of the installation. The physical location and the customer’s requirements are two other important things to consider, as well as reviewing the existing security procedures and perhaps establishing new ones. The areas to monitor and why, which cameras to use and where to place them, as well as the current network infrastructure are all key factors for a successful surveillance installation.
This guide will present the site survey considerations in five steps.
Establishing the purpose
The first step in designing a surveillance system must always be to define the purpose of the installation.
The most important steps in this process include interviewing the client and reviewing the site, to find out more about the business and its operations.
Example 1 – Purpose of surveillance system at Corporation A
- Visual coverage of the property’s rear boundaries and fences in general, as well as at specific vehicle entrances, and to document authorized access and prevent trespassing.
- Visual identification and documentation of all individuals entering and leaving the property through the south gate, to obtain an accurate count and identification of all individuals onsite in the event of an emergency.
- Event-driven recordings outside business hours, to reduce bandwidth and storage in the network.
Example 2 – Purpose of surveillance system at Corporation B
- Cameras 1-4 to provide general documentation of activity in the area
- Facial identification of all individuals entering via door 4 from 5:00 PM (17.00) to 07:00 AM (07.00).
- General monitoring of activity in the lobby at door 4 from 7:00 AM (07.00) to 5:00 PM (17.00).
Site survey framework
When planning your surveillance system, the physical location and the customer’s needs make up two of the building blocks of the site survey. A joint review with the customer of the existing security procedures and rules can help you identify areas for improvement. Doing a risk assessment to identify surveillance needs is a requirement, but it will also help you identify what the customer is trying to prevent and/or protect.
Other building blocks of the site survey include defining the overall requirements, specific areas to monitor and why, and the necessary levels of security. Another important aspect is the current infrastructure, such as the existing equipment, available lighting, cabling, and camera mounting conditions.
The site survey helps you identify areas of interest, some of them which may have been overlooked by the customer. Typical areas to monitor include the following:
- Emergency exits
- Car and pedestrian gates
- Cashier areas
- ATM machines
- Waiting areas & lines
- Reception areas
- Loading bays & delivery entrances
- Perimeter areas, fences, windows
Camera selection and positioning
When selecting and positioning cameras, it is important to know the client’s surveillance needs. Do you need to detect objects/persons, to recognize people, or do you need to identify unique facial characteristics? The operational requirement determines the level of detail required.
To define recognition, this means that the image can be used to identify someone already known to the observer, even if the person’s face is not completely visible or clear – as other visual factors (height, body size, gait, clothes, etc.) also play a part in recognition.
An image good enough for identification however, means that there must be enough detail to allow positive facial identification of a previously unknown person, when this image is compared to other images or when the person is physically present, and regardless of any other considerations.
Figure 2. The different resolutions for Identification, Recognition and Detection.
Although a single camera can provide an overall view of the scene, it might not provide enough detail to identify individuals. If this is one of the surveillance goals, then an additional camera needs to be included in the design, as in the figure below.
Figure 3. One camera providing an overall view, and an additional camera for identification.
Figure 4 illustrates how four fixed cameras cover most of the parking area, whereas a single PTZ camera can cover the same area, by panning around. However, a PTZ camera can only view one segment of the area at a time, while the fixed cameras provide coverage all the time.
Figure 4. Coverage areas for fixed versus PTZ camera.
This part of the survey involves verifying the existing equipment and functionality, to ensure that the network does what it needs to do, and to make sure the system will support future needs. Also check whether the system will support advanced features that might be required, such as Quality of Service (QoS), Power over Ethernet (PoE), and Virtual Local Area Networks (VLANs).
Also certify the existing cabling, to ensure that it is future-proof, and that it has sufficient capacity to handle the network load. Verify the performance by using network certification tools.
When creating a network, always use a star or redundant star topology, since these provide a minimized network load on each switch, a reduced load on the server, and a high level of redundancy. Never use a daisy chain infrastructure, as this is a vulnerable setup, with potential bottleneck issues and low redundancy.
Figure 5. Star topology
Power over Ethernet (PoE)
There are currently two standards available for PoE:
- 802.3af provides a maximum of 15.4 W per channel
- 802.3at provides up to 30 W per channel
To ensure that sufficient PoE power is available from a network switch, you need to calculate the total power consumption requirements for all the equipment connected to that switch. This total wattage requirement must be less than the switch’s PoE power budget.
Table 1 describes the minimum and maximum power consumption levels required for both the Power Sourcing Equipment (PSE) and the Powered Device (PD).
|Class||Usage||Power Output from (PSE)||Maximum Power Levels at the Powered Device (PD)|
|0||Default||15.4 W||0.44 – 12.95 W|
|1||Optional||4.0 W||0.44 – 3.84 W|
|2||Optional||7.0 W||3.84 – 6.49 W|
|3||Optional||15.4 W||6.49 – 12.95 W|
|4||Valid for 802.3at High PoE||30 W||12.95 – 25.5 W|
Table 1 Above. The minimum and maximum power levels for PSEs and PDs. Use these values when calculating the power budget of a system. Note that the maximum power available to a PD takes into account the invariable slight power loss over the network cable.
The PoE powering of a device becomes more critical depending on temperature. Many devices can function at different low temperature levels based on the amount of power available. It is imperative to verify that the correct midspan is used for exterior cameras. As seen in Figure 8, when high PoE is used, the AXIS P1344-E can operate at temperatures down to -40°C.
Figure 6: The datasheet for AXIS P1344-E shows that with High PoE, the camera can operate at temperatures down to -40°C.
Before installing a surveillance system, it is recommended to do a site survey and document it for future needs and upgrades.
One of the first things to define is the purpose of the installation. The location and the customer’s needs are also important things to consider, as well as reviewing the existing security procedures and establishing new ones. What areas to monitor and why, which cameras to select and where to place them, as well as the state of the current network infrastructure are also key factors for a successful surveillance installation.
Source = http://www.axis.com/sk/en/learning/web-articles/site-survey-considerations/index