When building a railway video surveillance system, it is necessary to take into consideration the special factors other than the conventional monitoring application systems according to the line application characteristics and the particularity of the environment, such as the following aspects:
Wind and thunder and lightning and other natural phenomena
Wind, rain, thunder, and electricity bring great challenges to outdoor cameras. Rain, snow, high temperatures, low temperatures, lightning strikes, and windy winds can cause a dramatic increase in the cost of system maintenance for each damage link. The characteristics of a railway project are spans. Large, it is often a mountain-high road, and sometimes it is still working at height, and once the system is opened, it will encounter many restrictions when applying for operations, resulting in increased costs. Therefore, the selection, installation, and wiring of the outdoor camera and the high quality of the camera itself are particularly important.
Long range camera problem
High-speed rail monitoring, according to points, is mainly divided into indoor engine room, indoor waiting room, ticket office and outdoor plaza, platform, etc. There is no special place for camera deployment in these locations, but another application with more points is along the railway line. The railway is a long-range camera, and a long-range camera may need to monitor tens of meters, a few hundred meters, or even a few kilometers. This means that a long-range camera may require a few kilometers of visibility. Looking at the camera is not a simple camera with a longer focal length lens. Simply speaking, when the focal length is pulled to a certain length, it is difficult for the manual keyboard to operate to locate a very distant object, that is, the microstep control function of the camera is very important. In addition, high-altitude camera, anti-jitter, night vision lighting issues need to be considered.
Preset accuracy
In high-speed rail monitoring, in order to quickly locate the scene or respond to alarms, customers usually set several preset positions for quick application calls in the future. The number of preset positions is usually not a problem. Currently, most cameras support 128 or even 256 preset positions, and actually The project will not use so much, but the accuracy of the preset position is an important indicator to examine the PTZ camera, for example, when the user set a preset position, usually called later, some camera presets will be offset , This had to manually fine-tune again, lost the significance of the preset position itself, affecting the use.
Encoder and DVR selection
In high-speed rail projects, encoders and DVRs are usually deployed in various site computer rooms. Therefore, encoders and DVRs require ultra-stable performance (embedded encoders and embedded DVRs are preferred), good networking capabilities, and remote management. Upgrade capability. Because the network system has a complex architecture, a large span, and many routes, the encoder device needs to have a local cache function. In the case of temporary network terminals, the video will not be lost. Once the network is restored, the video can be supplemented to the NVR storage. In addition, image clarity, dual stream support, two-way audio support, and the number of alarm inputs and outputs are all indicators that need to be considered.
Coding standard
At present, the railway project mainly uses MPEG-4 encoding technology and H.264 encoding technology. In the future, AVS encoding may be deployed. The temporal and spatial redundancy of video information may be removed by a combination of intra-frame compression and inter-frame compression. information. The delay of coding equipment shall not be greater than 300ms, the delay of each level of forwarding shall not be greater than 500ms, the delay of decoding equipment shall not be greater than 300ms, and the PTZ response delay shall not be greater than 500ms. The latency of the system front-end acquisition equipment to users shall not be monitored. More than 3s.
Wind and thunder and lightning and other natural phenomena
Wind, rain, thunder, and electricity bring great challenges to outdoor cameras. Rain, snow, high temperatures, low temperatures, lightning strikes, and windy winds can cause a dramatic increase in the cost of system maintenance for each damage link. The characteristics of a railway project are spans. Large, it is often a mountain-high road, and sometimes it is still working at height, and once the system is opened, it will encounter many restrictions when applying for operations, resulting in increased costs. Therefore, the selection, installation, and wiring of the outdoor camera and the high quality of the camera itself are particularly important.
Long range camera problem
High-speed rail monitoring, according to points, is mainly divided into indoor engine room, indoor waiting room, ticket office and outdoor plaza, platform, etc. There is no special place for camera deployment in these locations, but another application with more points is along the railway line. The railway is a long-range camera, and a long-range camera may need to monitor tens of meters, a few hundred meters, or even a few kilometers. This means that a long-range camera may require a few kilometers of visibility. Looking at the camera is not a simple camera with a longer focal length lens. Simply speaking, when the focal length is pulled to a certain length, it is difficult for the manual keyboard to operate to locate a very distant object, that is, the microstep control function of the camera is very important. In addition, high-altitude camera, anti-jitter, night vision lighting issues need to be considered.
Preset accuracy
In high-speed rail monitoring, in order to quickly locate the scene or respond to alarms, customers usually set several preset positions for quick application calls in the future. The number of preset positions is usually not a problem. Currently, most cameras support 128 or even 256 preset positions, and actually The project will not use so much, but the accuracy of the preset position is an important indicator to examine the PTZ camera, for example, when the user set a preset position, usually called later, some camera presets will be offset , This had to manually fine-tune again, lost the significance of the preset position itself, affecting the use.
Encoder and DVR selection
In high-speed rail projects, encoders and DVRs are usually deployed in various site computer rooms. Therefore, encoders and DVRs require ultra-stable performance (embedded encoders and embedded DVRs are preferred), good networking capabilities, and remote management. Upgrade capability. Because the network system has a complex architecture, a large span, and many routes, the encoder device needs to have a local cache function. In the case of temporary network terminals, the video will not be lost. Once the network is restored, the video can be supplemented to the NVR storage. In addition, image clarity, dual stream support, two-way audio support, and the number of alarm inputs and outputs are all indicators that need to be considered.
Coding standard
At present, the railway project mainly uses MPEG-4 encoding technology and H.264 encoding technology. In the future, AVS encoding may be deployed. The temporal and spatial redundancy of video information may be removed by a combination of intra-frame compression and inter-frame compression. information. The delay of coding equipment shall not be greater than 300ms, the delay of each level of forwarding shall not be greater than 500ms, the delay of decoding equipment shall not be greater than 300ms, and the PTZ response delay shall not be greater than 500ms. The latency of the system front-end acquisition equipment to users shall not be monitored. More than 3s.
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