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SPx Tracking Server

Tracking, Fusion & Distribution

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SPx Server, a component of the Cambridge Pixel SPx radar processing family, is a COTS radar data extractor and target tracker. Interfacing to hardware or network radar video, SPx Server accepts polar format primary or IFF radar video and processes it to identify targets, which are then correlated from scan to scan to output positional and motion updates.

The SPx Server software module is integrated with the SPx Processing library, which provides a comprehensive range of radar processing capabilities. After acquisition and prior to data processing, the video may be passed through the standard SPx processing functions to implement gain control, area-based video removal (masking), CFAR thresholding, interference suppression or other functions. Additionally, user-defined processes may be incorporated into the processing chain to allow a completely custom solution using SPx as the integrating framework.

When extracted data is correlated from scan to scan, the track correlator uses multiple hypotheses to support ambiguous interpretations of the radar video. The filter uses position, size, shape and historical measurements to correlate existing tracks with new data, providing updated positions and dynamics, as well as a confidence estimate. The behaviour of historical track data is analysed to help interpretation providing a first-level classification capability.

Optional video recording capabilities are available in the compatible SPx Record module that records the polar radar video to support, for example, incident recording or training applications.

Redundant Operation

Dual instances of SPx Server can be run to provide redundant operation for high reliability systems. The individual instances both run simultaneously, processing the same data in parallel and monitoring each other's status. In the event that the principal instance suffers a failure, the secondary instance detects this situation and automatically takes over transmission of video and/or track data onto the network. Receiving clients see a single consistent and uninterrupted stream of radar and target track data.

The SPx Fusion Server product can be used to support redundant operation, providing a consistent set of track IDs to clients in the event of failover.  SPx Monitor adds an invaluable layer of monitoring and diagnostics, showing which SPx Server is actively sending data onto the network. Additionally, SPx Monitor can add resilience to the system by automatically restarting applications which it detects have stopped. 

Target Extraction

The SPx Extraction process examines the processed video to search for target-like returns that form a connected target-like shape. A set of configurable parameters define the target size of interest, allowing small noise returns or larger clutter or land masses to be eliminated early in the processing.

The Extraction process begins by creating a set of spans that represent intervals of video above a threshold for each processed return. These spans are then combined across returns to form connected two-dimensional shapes. The weighted centre of gravity, bounding box and total weight of the plot shape are calculated and entered into a plot database, along with a timestamp. At this stage of the processing, no merging occurs of close plots that are likely to be derived from the same target. This allows partial plots to be reported on the network, if desired, and allows the tracking process to consider the merits of merging in the context of the local tracks.

Secondary Surveillance Radar Extraction

SPx Server supports target tracking from secondary surveillance radar (SSR) transponder video, including decoding of the interrogation mode information. If the SSR/IFF transponder video is sampled with sufficient resolution, the plot extraction process within SPx Server is able to extract codes from interleaved mode 1, 2, 3/A and C responses. This information then forms part of the plot and is passed onto the tracker to assist with tracking.

Interrogation mode tags may be embedded at the start of the IFF video stream as P1/P3 pulses or a specific mode specified, telling SPx Server which responses to expect. The processing includes de-FRUITING and de-garbling to remove typical noise from an IFF video.

SPx Server's IFF video handling capabilities provide a viable, highly cost-effective alternative to traditional hardware-based IFF decoding systems.

Track Creation

The tracker maintains an active track database. The contents of the database are updated with new plot data derived from the data extraction stage. New tracks are added to the database from either a manual request (perhaps derived from an operator or else an external process), or else automatically.

The automatic track creation occurs when plots entered into the database are seen to be uncorrelated, or ungated, with any existing known target. A new preliminary track is created and is updated with future detections until confidence is established that the track is likely to be a target of interest.

The time a track is held in the preliminary stage is a programmable option and needs to be set to balance the speed of detection with the likelihood of a false alarm. In a low clutter environment, where extracted plots are likely derived from real targets, the acquisition time may be as short as 2 detections. For noisy situations, where the plot extractor is reporting false detections, the integration time in the preliminary stage may be extended.

Multi Hypothesis Tracking (MHT)

The SPx Tracker uses multi-hypothesis association. This offers significant improvements in performance over simpler single-hypothesis trackers. The role of a tracker is to interpret radar observations to distinguish real targets from noise, and to construct models to describe the motion of the true targets. The tracker is provided with data, typically in the form of plots, derived from the processing of the radar video. These plots are connected regions of radar video that satisfy some rules of position, amplitude, size and signal strength. Unfortunately, measurements from the radar are imperfect. There will be noise from the measurement process, clutter from the environment and unpredicted manoeuvres of the targets of interest. This means that the tracker will be presented with noisy and possibly multiple measurements from the target of interest. The tracker's responsibility is to provide the best interpretation of the data using assumed or calculated statistics for the noise and the likelihood of change.

In the single hypothesis situation, the tracker is forced to make the best interpretation it can of the available data at each update. For some updates, where there is a clear interpretation of the measurement, the best interpretation may be obvious and the single hypothesis offers a satisfactory solution. Problems arise, however, if the interpretation of the measurements is not obvious. In this case it may be desirable to defer a decision until the next update when additional information will help to decide on the correct interpretation. The ability to simultaneously consider multiple interpretations of the system is the key to the multi hypothesis tracker.

Model Based Tracking (MBT)

The MBT extensions to SPx Server (V1.72 onwards) provide a new capability for target initiation and tracking. The new track initiation method is significant because it can handle larger number of provisional tracks than the standard MHT's initiation process. This new tracking capability allows specific target models to be created, meaning that different parameter configurations can process the same radar video. The ability to detect small targets and support multiple tracking modules may offer new opportunities for tracking.

This extension to SPx Server is described here.

Track Filter

For each hypothesis, the tracker updates the current estimated position with the new measurement. If the measurement were known to be completely accurate, the update process would believe the measurement and the new estimate would be exactly the measured value. For various reasons, the measurement is inaccurate so the update process must take a weighted combination of the expected position and the measured position. This is the track filtering. SPx offers a number of track filtering modes. The simplest mode uses fixed gains in the components of the measurement. This can be successful for tracking applications where the target is clearly identified and relatively clutter free.

The filter works by computing a dynamic filter gain, K, based on estimated system noise and measurement noise models. The system noise is used to model uncertainty in the known dynamics of the target, including its ability to manoeuvre. As system noise increases, or equivalently as measurement noise decreases, the filter places more weight on the measurement so the filter gains increase. As system noise decreases or as measurement noise increases, the filter gains decreases causing less emphasis to be placed on the new measurement. The filter gains are continually changing and provide, under certain assumptions of the noise characteristics and linearity, an optimal estimation of the true target position.

Tracking Parameters

The behaviour of the tracker may be configured through a set of tracking parameters. These parameters may be set initially from a configuration file and may be adjusted during operation of the tracker using either a customer GUI or network interface. The parameters control many aspects of the tracker's performance including:

  • Min/max speed of target to be tracked
  • Multi or single hypothesis association modes
  • Fixed gain or adaptive gain
  • Expected target dynamics
  • Size limitations on targets to be tracked
  • Measurement noise estimates
  • Multi-function primary and secondary (IFF) radar processor
  • Radar video from HPx cards or network
  • Radar processing
    • Filtering
    • CFAR Thresholding
    • Area-based video filtering/masking
    • Clutter map generation
  • Plot Extraction and merging
  • AIS track display and recording
  • Multi-hypothesis target tracking
  • Model-based tracking extension
  • Fully configurable tracking
  • Area-dependent tracking parameters
  • Full auto track initiation
  • Redundant operation, with automatic failover
  • Built-in world coastline database
  • Static or moving platform
  • NMEA navigation input for ship systems
  • Radar network distribution
  • Radar, NMEA and AIS record/replay
  • Comprehensive configuration GUI
  • Windows or Linux versions
  • Network remote control
  • Receipt and tracking from plot data
  • Receipt and distribution of lidar data
  • Video, plot and track output to network
  • Fully configurable for:
    • Vessel traffic systems (VTS)
    • Surface movement radars
    • Air defence
    • Security (personnel, vehicles etc.)
    • Military naval
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Product Options

Component Supply: Available as software CD, Documentation and hardware interface card for OEM system installation
System: Available as complete server installation configured in PC-based system or single board computer
Licensing options for: Radar video distribution
Plot extraction
Target extraction
Record and Replay

System Requirements

Processor: X86 architecture
Recommended processor is Intel Core i5 or higher. Minimum 4GB system memory recommended.
Operating System: Windows 10
Linux (Fedora, Ubuntu, RHEL)
For other operating systems consult factory
Graphics: Requires 1024 x 768 graphics display or higher for maintenance and configuration. Recommended PCIe or XMC graphics card. GUI is not needed for operational system.
Disk: Disk storage is optional for radar video recording.
Network: 100 Mbit or 1 Gbit Ethernet adaptor recommended.
Expansion Slot: PCI, PCIe or PMC expansion slot required if using a HPx radar interface cards. Refer to the user manual for these cards for full details.

Software Licensing

Licensed Functions: Radar video distribution
Plot extraction
Target extraction
Record and Replay
Moving platform
Licence Protection Method: USB Dongle
MAC-address licence file
(other schemes are possible, consult factory for details)

Radar Interface

Radar Input: Hardware interface card: HPx200/200e/250/400e/346
Network input from supported radar types
Radar Trigger: PRF: up to 10kHz with HPx cards
Amplitude: Up to 30V. Single-ended (opto-coupled) or differential (RS422)
Impedance: 75R or high impedance
Radar Video: Amplitude: 5V (positive or negative)
Impedance: 75R or high impedance
Azimuth - ACP/ARP: Single ended signal up to 30V or differential RS422

ACP count: 60, 180, 300, 360, 1024, 2048, 4096, 8192, 16384 pulses per ARP.
Software automatically detects ACP count.
ACP Interpolation supported for low counts.

ARP: 1 pulse per scan

Rotation rate: up to 240rpm
Azimuth - Parallel: 12 bit RS422 differential azimuth value with data strobe
Azimuth - Synchro/Resolver: 115V reference voltage, 90V synchro (3 wire) or resolver (4 wire) input. Reference voltage is standard 115V input. (Other synchro voltages on request)
Note: Synchro/resolver input requires use of HPx-180 synchro/resolver to parallel converter PCI card.
Plot Inputs: Option to receive plot data from proprietary radars. Consult factory for details.

Navigation Information

Platform Navigation: NMEA-0183 input
GPRMC, GPHDT, GPHDM sentences used, interpreted by server.
Physical Interface: Standard serial port on PC or single board computer
Network input (uses NMEA 0183 sentences in network packets)
Navigation Reporting: Optional network distribution of NMEA sentences received on serial port
Programmable IP and port address for output
North Offset Adjustment: Incoming azimuths may be ship or North referenced, with automatic conversion to North referenced from navigation data, as required.


Video Processing with HPx Radar Interface cards

Video Bandwidth: 25 MHz
(When used with HPx-200, HPx-200e or HPx-250 radar interface cards)
A-to-D Conversion: Programmable 2 to 50 MHz sampling rate. 12-bit high-performance capture.
Data is reduced to 8-bits through a programmable LUT.
Threshold Detection: Adaptive threshold CFAR technique with geographical area thresholding
Clutter Processing: Software-based scan-to-scan correlation
Clutter subtraction
Land mass blanking


Land Mask: Static mask: complex polygon of any shape or size, optionally containing holes.
World vector shoreline: land masking using built-in database of world shoreline data (static or moving platforms supported).
Polygon set is defined in world x,y coordinates and is automatically converted into polar space. Typical azimuth resolution is 0.18 degree and range resolution matches input data resolution.
Area Dependent Processing: Tracker parameters can be assigned different values in different areas (static platforms only).
Polygon set is defined in world x,y coordinates and is automatically converted into polar space. Typical azimuth resolution is 0.18 degree and range resolution matches input data resolution.
Automatic Initiation Areas (ATI): Static mask. Complex polygons defined in x,y coordinates. Can be any shape or size.
Independent areas can be configured for radar processing, track initiation and tracking.
Optional automatic suppression of plots over land areas using world vector shoreline database (supplied as standard).
Plot Extraction: Configurable plot geometry (min/max range and azimuth)
Optional plot merging (multiple modes)

Digital Video Distribution

Network Distribution: Distribution onto LAN of radar video data in polar format
Compression: ZLIB or ORC (Open Radar Coding)
Data Rates: Highly dependent on input data and configured resolution.
Typical figures from 2 Mbits/sec for processed video to 10 Mbits/sec.
Network Protocol: UDP - Unicast or Multicast distribution
Video Store for Distribution: Raw input data
Processed data
Clutter map
(One of above with standard server. Multiple channels of distribution are supported with customised server variants, including options for multi-resolution data)

Target Tracking

Maximum number of targets: 500 (typical, but not limited by software)
Track Initiation: Automatic, with programmable extraction areas defined as polygons or range-azimuth segments (static radar only)
Automatic wake area elimination (configurable geometry)
Shadow area elimination from known targets
Manual track initiation from remote system
Configurable min/max initiation speeds, which may be area dependent
Max initiation speed: 1000 m/s
Minimum initiation range at maximum speed:

10NM for targets moving tangential to radar
3 NM for targets moving radially towards or away from radar
Programmable initiation time from 2 scans upwards using M:N or SPRT integrator. Initiation criteria may be area dependent.
Signal to Clutter: Typically 8 dB or higher expected
Target Speeds: Programmable minimum and maximum target speed for initiation in the range 0 to 1000 m/s
Programmable minimum and maximum target speed for tracking in the range 0 to 1000 m/s
Tracking Performance: Figures are highly dependent on sensor, operating conditions and configuration data.
Sample configuration - sea state 1, 100m2 RCS target:
For radar range 200NM, target at 100 NM
  • Position accuracy: σ = 90m
  • Range accuracy: σ = 90m
  • Azimuth accuracy: σ = 10 secs arc
  • Speed accuracy: σ = 5% of true speed for speeds above 5 m/s, σ = 10% of true speed for speeds below 5 m/s
  • Course accuracy: σ = 1 degree
For radar range 70NM, target at 35NM
  • Position accuracy: σ = 25m
  • Range accuracy: σ = 25m
  • Azimuth accuracy: σ = 10 secs arc
  • Speed accuracy: as above
  • Course accuracy: as above
For radar range 35NM, target at 18NM
  • Position accuracy: σ = 20m
  • Range accuracy: σ = 20m
  • Azimuth accuracy: σ = 10 secs arc
  • Speed accuracy: as above
  • Course accuracy: as above
Notes: Performance figures are typical, but depend on exact characteristics of radar and target. Target assumed to be moving in straight line. If server is applying North offset compensation, timely updates of ship's heading are critical for good tracking performance. Quoted values of σ are standard deviations of errors.

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