Hong Kong Observatory Format
The HKO (Hong Kong Observatory) format uses an 8-bit data stream and can transmit an image of and rectangular product up to 255 pixels high with compression for horizontal runs of the same data.
For flexibility, IRIS supports a mapping table to convert the IRIS product color levels to the transmitted levels. The expanded color scales with more than 16 colors are not available for link outputs.
 | Here, hexadecimal notation is denoted with the -h suffix. For example,
12h means 12 base 16, or 18 base 10. Also for this discussion, all line and pixel numbers are
origin 1. The upper left pixel is line 1, pixel 1. |
The format of picture transmissions is as follows:
- Picture type ID code
- Header code
- Data section
- End-of-image code
The data section consists of a series of line number codes, each followed by compressed data. Data for a line ends when the next line number code is encountered. All unfilled pixels are assumed to be of the value 1. If a line is repeated in the data stream, any new data overwrites old data. If a line number code is never transmitted, the line is assumed to be filled with ones.
The only use of a 0 byte is to immediately proceed on the following commands. This make it easy to sync with the data stream.
00h 01h — Picture type follows in the next byte
| 1 | All PPIs | |||
| 2 | CAPPI | >2.5 km height | <96 km range | data not velocity |
| 3 | CAPPI | all heights | <96 km range | data is velocity |
| 4 | CAPPI | <2.5 km height | <96 km range | data not velocity |
| 5 | CAPPI | >2.5 km height | 96<range<192 | data not velocity |
| 6 | CAPPI | all heights | 96<range<192 | data is velocity |
| 7 | CAPPI | <2.5 km height | 96<range<192 | data not velocity |
| 8 | CAPPI | all heights | >192 km range | data not velocity |
| 9 | CAPPI | all heights | >192 km range | data is velocity |
| 10 | All other products |
00h 02h — Header follows in the next 40 bytes
The format of the header is HHPPPPPPPPPPPPhh:mm DD-MM-YYYY. Where
HH is the CAPPI height in km and PPPPPPPPPPPP is
the product name.
All numeric fields are two digits, with leading zeros, if required.
00h 03h — Line number follows in the next byte
The following byte contains the origin 1 line number in the range 1–255. This is followed by a variable length string of bytes containing a data number followed by a repeat count. Data numbers are in the range 1 through 16.
00h 04h — End-of-Image
This indicates that an image has been completely sent. Any future transmissions relate to another image.