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The IP address and port used by the radar to send CAT-240 message are configurable options. By default, the following address and port are used:
IP address | TBD |
Port | TBD |
Table 1 - Default IP address and port for CAT-240 data
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The structure of the message data block is shown in Figure 2
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CAT | The message category. Always 240 (0xF0) |
LEN | The overall message length, including this data block |
FSPEC | Feature specifications for this message. |
Feature Specifications
The Feature Specification bit field structure defines which fields are present in the message and, in the case of optional features, which option(s) have been selected.
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The video header is structured as shown in Figure 4. CAT-240 field references are provided for cross-reference.
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SAC_SIC | System Identification Code / System Area Code |
TYPE | Message type. Always 001 |
MSG_INDEX | Incrementing message counter |
START_AZ | Start angle for data, encoded as 1/360 of a degree. |
END_AZ | End angle in encoded as 1/360 of a degree. |
START_RG | The starting bin for this message; where 0 is the bin closest to the radar |
CELL_DUR | Size of a bin in femtoseconds. |
RES_C | Defines the resolution (number of bits) for each bin; and whether the data is compressed. |
NB_VB | Size of the FFT data, in bytes. |
NB_CELLS | Size of the FFT data, in bins. |
Data Source Identifier
The Data Source Identifier provides a unique identifier for the radar source. The Data Source Identifier is a 16-bit field structured as shown in Figure 5.
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For Navtech, the values of the SIC/SAC values are set to
System Area Code | TBD |
System Identifier Code | TBD |
Start & End Azimuth
A Navtech radar outputs its FFT data on discrete azimuths. The number of azimuths sampled per rotation depends on the radar; and is configurable.
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Note, for Navtech radars, only 8-bit or 16-bit data will be transmitted.
Value | Resolution | Encoding, in bits |
1 | Monobit | 1 |
2 | Low | 2 |
3 | Medium | 4 |
4 | High | 8 |
5 | Very high | 16 |
6 | Ultra high | 32 |
Data Size In Bins
The number of bins in the message is calculated as
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CAT-240 frames video data into fixed-sized blocks. The size of each block and the number of blocks depends on the size of the FFT data.
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REP | The number of blocks in the Video data block |
block [n] | A block of FFT data. The size of the block is determined by the configuration in the video message header. |
Video Data Block Size
The framing configuration for an incoming message is specified with two fields:
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The block size is defined in the table below. Note, the data volume flags are mutually exclusive; at most one of the fields must be set.
Feature specification field | Block size, N (bytes) |
Video data low volume == 1 | 4 |
Video data medium volume == 1 | 64 |
Video data high volume == 1 | 256 |
If the number of bytes in the FFT data is not an exact multiple of the video block size, then the number of video blocks is rounded up. Any unused bytes used to pad the last video block are set to zero.
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For Navtech radars, the Special Purpose field is defined in Figure 9.
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Count | The size of the Special Purpose field, in bytes |
Seconds | Timestamp. UTC seconds since the Unix epoch (01 Jan 1970, 00:00) |
Subseconds | Nanosecond resolution field of the timestamp |
Azimuths per rotation | Total number of azimuths sampled per rotation |
Range in bins | The range of the radar, expressed as a number of bins |
Rotation speed | Current radar rotation speed, in milli-Hz |
Gain | Range scaling factor. Encoded as a IEE 754 binary32 (float) |
Offset | Range offset of the FFT data, in metres. Encoded as a IEE 754 binary32 (float) |
Health | Radar component health status |
Radar Health Status
Radar health status provides information on the current operating status. The field is encoded as a bit field, as shown in Figure 10.
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Each bit field is encoded with two bits. The value of the bits indicates the health status of the property, as shown by the table below.
Value | Definition |
|---|---|
0 | unhealthy |
1 | warning |
2 | healthy |
3 | Invalid / unknown |
Endianness & Field Layout
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