Design of video surveillance systems.
The design of any technical system is carried out on the basis of state regulatory documents. Any project must contain justified references to them.
The existing regulatory documents in Russia, specially developed for video surveillance systems 10 years ago, now do not always provide comprehensive answers to all questions relevant to installers. Currently, there is an active discussion about the need to adopt a new, more detailed standard. But until there are new regulations, the design of video surveillance systems must be carried out in accordance with existing documents.
The main modern Russian state standard for video surveillance systems «GOST R 51558 — 2000 Security television systems» was put into effect on 26.01.2000, developed by the Scientific and Research Center «Security» of the Main Directorate of the Ministry of Internal Affairs of Russia. It defines a security television system (STS) as a closed-circuit television system for receiving television images, service information and alarm notifications from a protected facility.
Mandatory devices for all STS:
— television camera;
— video monitor;
— power source, including backup power supply;
— connecting lines.
Devices that are optional for specific SOTs: video signal control and switching devices, motion detector, video storage device, auxiliary equipment.»
The following functional characteristics are mandatory for all systems: — television image analysis using one or more TCs;
— synthesis of television images received from all TCs;
— target tracking;
— priority display of alarm events;
— alarm about unauthorized actions.
In this case, the value of the system response time to an alarm event must correspond for each video channel of the system to the value specified in the technical specifications and/or in other technical documentation for specific systems:
The characteristics of the standard target for the SOT in the mode with a motion detector are used from GOST R 50658-94 (IEC 60839-2-4:1990) “Alarm systems Part 2. Requirements for security alarm systems.
According to GOST R 50658, a standard target is defined as «a person weighing 50-70 kg, 165-180 cm tall, wearing a cotton robe.» It is used when testing for compliance with functional requirements: establishing detection zone boundaries, detector sensitivity with an object moving at a constant speed and with uneven movement, and detector recovery time to standby mode. This is used when assessing a SOT with a motion detector.
GOST R 51558-2000 regulates that GOST 15.005-85 «System for development and launching of products into production. Creation of products of single and small-scale production, assembled on-site» is applicable to video surveillance systems. International standards are in effect in Russia, in particular, the European standard EN 50132-7, which contains general requirements for the placement and installation of CCTV control devices for security, which consist of camera(s), monitor(s) and/or device(s) for video recording, switching, control and auxiliary devices.
EN 50132-7 describes a method for testing and adjusting a video surveillance system using a test sample known as Rotaktn. Rotaktn is a plate simulating a human silhouette. It has high-contrast stripes and a gradation wedge. These markings are intended as a means of assessing resolution. Rotaktn can also be used to test detection zones, determine acceptable image height, image clarity and contrast.
In Russia, system resolution is measured using specially developed methods and/or using GOST 23456-79, which was developed for broadcast television back in 1979 and is still in effect.
The design methods are described in more detail in Recommendations R 78.36.008-99; further in the text of this article, the design methodology is given taking these recommendations into account.
In order to make the most of the advantages of video surveillance devices and achieve the desired result for the customer, the video surveillance system must be designed correctly.
At the first stage, it is necessary to examine the object and clearly answer the following questions for yourself by filling out the appropriate table:
1. Defining the tasks (detecting the fact of a person's appearance or reading car numbers).
2. Determining the need to use color cameras (analysis of the behavior of individual violators in a crowd, the appearance of a person in a protected area — the importance of recording the color of clothing) or black and white cameras, but with increased resolution (workplace monitoring).
3. Determining mandatory viewing areas (windows, doors, conveyor belts).
4. Determining the admissibility of the presence of blind spots and the need for cross-observation of cameras by each other.
5. Determining the need to use PTZ cameras with optical zoom, controlled by an operator.
6. Determining the need to control small and low-contrast details.
7. Determining the level of illumination at the object, the presence of bright highlights, reflective objects, objects creating shadows (trees, etc.).
8. Determining the need to record an image in low illumination, in conditions of changing illumination over a wide range.
9. Determining the need to record fast-moving objects (car license plates on the highway, work in casino gaming rooms, conveyor belts) or simply a person entering the door.
10. Determining the possibility of installing, fastening cameras, and connecting them to communications.
11. Determining the possibility and feasibility of supplying 220V
12. Determining the presence of difficult climatic conditions at the site (dust, high humidity, sudden temperature changes, resin fog, explosion hazard).
Then it is necessary to make the following calculations and select the appropriate equipment:
1. Calculating the focal length, viewing areas obtained from each camera.
2. Calculation of dead zones.
3. Determining the location of cameras and their number.
4. Determining the resolution of the equipment.
5. Determining the need and conditions for using electronic zoom (selection of appropriate monitors).
6. Calculating the storage depth of the archive and its contents (alarm recording, continuous recording, recording and viewing speed).
7. Determining the number of operator and administrator workstations with the appropriate access rights to cameras and setup functions.
8. Calculating network bandwidth.
9. Selecting equipment to provide video signal transmission over the network.
10. Calculating supply voltage characteristics, calculating equipment to provide supply voltage.
11. Determining the need for additional functions (appearance/disappearance of stationary objects.
12. Selecting cameras with analog or IP output.
Let's dwell on the details of these calculations.
The European standard EN 50132-7 recommends the following gradations of surveillance system efficiency: verification, recognition, identification. It is possible to notice a person in an image obtained from a standard CCTV camera if the person is at a distance of about 20 meters. A familiar person can be identified from a distance of 5 meters, an unfamiliar person – from a distance of 2 meters. A car number can be recorded from a distance of 4 meters. These conditions determine the geometry of the arrangement of cameras and their number.
Taking into account the above, it is necessary to determine the zones that the consumer wants to protect with the help of a video surveillance system, i.e. video surveillance zones. As a rule, these zones are the most likely places for intruders to enter (doors, windows, etc.) and places where material assets are directly concentrated (warehouse, cash register, sales area, management offices, etc.). There can be any number of video surveillance zones: from one or two (for example, the entrance door and sales area) to several dozen or hundreds, including most of the premises of the facility. In this way, the approximate number of cameras in the system is determined and, consequently, other necessary equipment for equipping video cameras, processing the signal, displaying video information, etc.
Then the focal length of the camera lenses is calculated.
For a 1/3” inch matrix
f = 3.6* D/V
f= 4.8*D/H, where
f is the focal length, mm
D is the maximum distance to the object, m
V is the height of the object, m
H is the length of the object, m
For a 1/2” inch matrix
f = 4.8* D/V
f= 6.4*D/H, where
f is the focal length, mm
D is the maximum distance to the object, m
V is the height of the object, m
H is the length of the object, m
From the obtained values, the focal length of the lens is selected either equal or to the nearest shorter side (to match the range being produced).
Then the equipment must be selected based on its resolution. Due to losses when passing the signal over the network, the resolution will deteriorate from unit to unit of the system. Therefore, it is better to choose cameras with a resolution greater than or the same as that of the video recorder (not less). It is recommended to choose a monitor with a resolution no greater than that of the video recorder. For systems based on cameras with an IP output, the monitor can be selected with a resolution provided by the electronic zoom of the system (or approaching it).
«Dead zones» are also determined — the unviewable part of the control zone under the video surveillance camera (L = L 1 + h tg (b — a v /2)), where:
h — the height of the video camera installation,
a v — the vertical viewing angle,
L 1 — the distance from the wall to the lens,
L — the size of the dead zone,
b – camera tilt angle (angle between vertical axis and camera axis).
As a rule, one camera is placed in the visibility zone of another camera.
The required camera sensitivity is set during the inspection of the object, and the consumer must determine the illumination at the object not only during the day (working), but also at night and, if necessary, decide on the presence of emergency lighting or infrared illumination.
Examples of typical illumination levels:
— daytime illumination before sunset: 50 lux;
— a well-lit motorway at night: 10 lux;
— a staircase or corridor: 60 lux;
— an office or store: 250-500 lux.
The result obtained (the illumination of the image sensor) must be higher than the sensitivity of the video camera.
The algorithm for determining sensitivity according to the recommendations of R 78.36.008-99:
— using a lux meter (or in some other way), measure the illumination in the control zone of the protected object;
— the value of the reflection coefficient of the real control object OK is determined according to the table.
Then the transmission coefficient is determined according to the specified in the description aperture ratio of the lens selected for this camera according to the table.
The minimum illumination E sensor that can be obtained in the camera control zone is calculated using the formula:
E sensor = E scene*R*K , where
E sensor is the illumination on the camera's photosensitive element,
E scene is the illumination in the camera control zone,
R is the reflection coefficient of the control object,
K is the transmission coefficient.
If necessary, infrared illumination is selected and installed.
The illumination angle should match the viewing angle of the video camera, and when choosing illumination, it is better to choose an illumination angle slightly smaller than the viewing angle of the video camera. This recommendation is based on the fact that usually on a monitor, part of the image goes beyond the visible part of the screen, in addition, the periphery of the image is usually not very important. It should be taken into account that an IR illumination device with the same radiation power, but with a narrower angle, shines further.
The most appropriate are low-power IR illuminators, which have illumination angles of 40° and 70° (as a rule, short-distance video cameras with an angle of less than 40° are rarely used).
The illumination of the object within the frame must be uniform, otherwise the low-contrast details of the object image will be poorly processed. This is especially dangerous in night conditions, when unlit areas of the object may fall into the field of view of the video camera. This can lead to a significant part of the dynamic range in contrast being «eaten up» by an uninformative difference between the illuminated and unlit areas of the image on the monitor, while the low-contrast details in the mentioned areas will be practically indistinguishable.
Black and white video cameras compatible with IR illumination «see» in the IR spectrum, but somewhat worse than in the visible spectrum, and with increasing wavelength their sensitivity decreases. Thus, infrared illumination with a shorter wavelength is preferable (in terms of illumination efficiency). At the same time, LEDs (emitters) with a wavelength of 870 nm are visible to the naked eye. All this means that when using IR illumination at short distances (up to 10-15 meters), IR spotlights with a wavelength of 870 nm are not always suitable, and it is necessary to compromise between efficiency (870 nm) and stealth (930-950 nm). When using infrared spotlights at long distances and at small radiation angles, efficiency is more important, since it is difficult to visually find such spotlights.
Calculation of the size of the video recorder archive for recording information from cameras with a tax exit is made based on the following considerations:
12 kb — compressed frame size
76 hours — 3 days — archive storage time
168 hours — 7 days — archive storage time
336 hours — 14 days — archive storage time
25 fps, 11 fps, 6 fps — recording speeds
18 — number of cameras. The number of video recorder channels is selected based on the number of connected cameras. It is customary to select video recorders with a 10% reserve in the number of inputs compared to the designed number of cameras to allow for emergency expansion of the system. Therefore, we will perform calculations for both 18 and 20 camera connection channels.
12 kb × 25 fps × 18 channels × 76 hours × 3600 s = 1.48 TB
12 kb × 25 fps × 20 channels × 76 hours × 3600 s = 1.64 TB
12 kb × 11 fps × 18 channels × 168 hours × 3600 sec = 1.44 Tb
12 kb × 11 fps × 20 channels × hours × 3600 sec = 1.6 Tb
12 kb — 6 fps — 18 channels — 336 hours — 3600 s = 1.57 TB
12 kb — 6 fps — 20 channels — 336 hours — 3600 s = 1.74 TB
The operating system takes up about 1.2 GB. Therefore, when choosing hard drives, you need to add up the archive size and the size occupied by the operating system. In addition, it is necessary to choose the size of the hard drives with a reserve, since the size of the compressed frame can vary depending on the degree of information saturation of the frame and the compression format up to 40 kb.
An example of calculating the archive size and viewing it for a camera with an IP output.
Let's say the video surveillance system contains 72 cameras. With a resolution of VGA at 50% JPEG quality, we take the size of each frame to be 40 kb.
The archive size is calculated when recording at a speed of 12 fps for a month
Calculation: 40 kb x 12 (k/sec) x 60 (sec) x 60 (min) x 24 h/day x 72 cameras x 31 days = about 9,288.35 TB for all 72 cameras per month.
Archive size per camera per day: 4,139.55 GB
Archive size for 72 cameras per day: 2.85 295 TB
To store an archive of about 10 TB, we recommend the following hardware configuration: 3 servers (IBM X306M, HP Proliant DL140, Dell PowerEdge 850 or similar) and RAID arrays (Infortrend Eonstor or similar). It is recommended to have 4 TB on each server so that the system does not fail if the customer starts viewing, searching and recording simultaneously. In addition, you need to have free space on the servers in case the customer wants to expand the system.
The current image and archive can be viewed from any point, using 3 computers and software for convenience.
Each camera has its own recording volume on the RAID array connected through the server using a ring buffer. When configuring the camera, the installer must specify in the camera settings how much space is allocated to it through the server. In our case, the camera records 4.1 GB per day, so it is recommended to allocate 130 GB on the camera disk. (after filling this space, the computer will start writing new fragments “over” the old ones). Recording new information over the old one is also used in video recorders to record information from cameras with an analog output.
(Continued in the next issue)