JSON Format for Input/Output ¶

Contents

JSON Format for Input/Output

Purpose ¶

The JSON object notation format was chosen because numerous reader are available, and it’s also human-readable. The structure has its focus on values, rather any descriptive elements, as it is the same with binary BUFR.

Decode BUFR to JSON Output ¶

To decode a BUFR into a JSON object, either use the instance method Bufr.decode() or the command-line parameter -j | --decode-json.

Encode JSON Input to BUFR ¶

To encode a file with a JSON object into binary BUFR, either use the instance method Bufr.encode() or the command-line parameter -e | --encode.

JSON Structure ¶

The content of an input and output file as formatted following the JSON structure consist of one list [...] as top-level element.

Each entry in this list represents one BUFR message.

One BUFR message is build as a dictionary {...} with following keys:

“index” : integer value, equal to the list index of this BUFR in the top-level list.
“file” : optional, set if the command-line scripts are used for decoding and encoding:
- Original file name, if a file was decoded.
- File name used for encoding.
“heading” : optional,
- Set if the decoded file contained a WMO bulletin.
- Used as WMO abbreviated heading line for a WMO bulletin on encoding.
“bufr” : the value representation of the BUFR.

Example:

[{
    "index": 0,
    "bufr": [ ... ],
    "heading": null,
    "file": "207003.bufr"
}]

The value representation of one BUFR is one list [...], its elements are the BUFR sections 0 to 4, where each is a list of values.

Length identifyer ¶

In contrast to the binary BUFR, there are NO length values denoting either the length of a section, or the ammount of repetition. On encoding they will be calculated, thus making the handling of delayed replication easier.

Booleans, None, Strings, and Numbers ¶

With JSON, boolean values are encoded as true or false, which is the case for some flag-values in sections 1 and 3.

In the data section 4, for any missing value the keyword none is set in the JSON structure.

Strings, or character sequences, are stored as sequences of ITA-5 (which is equivalent to US-ASCII) characters, surrounded with double-quotes ". When encoding a JSON object as BUFR, the underlying functions take care of padding/truncating the strings to match the width as defined by the descriptor.

Numbers are … numbers. Either integer or decimal-point values.

Section 0 – Indicator section ¶

Always has exactly two elements:

the keyword "BUFR".
the BUFR edition number.

["BUFR", 3],

Section 1 – Identification section ¶

The identification elements, or meta-data, of this BUFR.

The elements meaning follows the same order as encoded in BUFR according to the BUFR edition.

Although the representative time is encoded in BUFR Ed.3 without a value for the seconds, they are always set in the JSON structure – in which case they are set to zero. On encoding a JSON structure into BUFR Ed.3, the value for seconds will be ignored.

[0, 0, 98, 0, false, 21, 202, 15, 0, 2012, 11, 2, 0, 0, 0],

Section 2 – Optional section (local data)¶

This section is optional in encoding a BUFR, but the corresponding list entry is required.

Empty section:

[],

If the local data section 2 should not be present in the BUFR when encoding or decoding, the list representing the values of this section shall be left empty.

Section with values:

["03", "59", "7d", "ca", "7d", "20", "00", "53", "10", "94"],

If data for local application use either was encoded in the BUFR or should be used when encoding a BUFR, the numerical ASCII values of all bytes shall be listed, each wrapped with double-quotes to set string values.

Section 3 – Data description section ¶

Values listed in the following order:

Number of data subsets.
Data category flag.
Data compression flag.
Collection of descriptors which define the form and content of individual data elements.

[2, true, true, ["310060"]],

Section 4 – Data section ¶

Binary data.

Section 5 – End section ¶

Always has exactly one element: the keyword "7777".

["7777"]

Full Example ¶

[{
    "index": 0,
    "bufr": [
        ["BUFR", 3],
        [0, 0, 98, 0, false, 21, 202, 15, 0, 2012, 11, 2, 0, 0, 0],
        [],
        [2, true, true, ["310060"]],
        [
            [224, 160, 620, 3, 2012, 11, 2, 0, 0, 27.584, 6675220.0, 2628450.5, 696570.75, 4.96669, 24.54144, 25.41, 282.91, 150.05, 111.28, 1, 1, 9, 7, 5258, 597, 829880.0, 1.0, 0, null, null, 2048, 0, [
                [2, 65000.0, 109500.0, 1, 713, 0, 1024],
                [3, 121000.0, 175000.0, 714, 1146, 0, 1024],
                [4, 215500.0, 255000.0, 1147, 1305, 0, 1024]
            ], null, 0, 0, [
                [1, 0.0462895],
                [2, 0.0454931],
                [3, 0.0421172],
                [4, 0.0453741],
                [5, 0.0431189]
            ]],
            [224, 160, 620, 3, 2012, 11, 2, 0, 0, 27.584, 6675220.0, 2628450.5, 696570.75, 5.05004, 24.3926, 24.2, 281.97, 150.22, 111.22, 1, 1, 9, 8, 5258, 538, 829880.0, 1.0, 0, null, null, 2048, 0, [
                [2, 65000.0, 109500.0, 1, 713, 0, 1024],
                [3, 121000.0, 175000.0, 714, 1146, 0, 1024],
                [4, 215500.0, 255000.0, 1147, 1305, 0, 1024]
            ], null, 0, 0, [
                [1, 0.0469285],
                [2, 0.0458891],
                [3, 0.041389],
                [4, 0.0447059],
                [5, 0.0430633]
            ]]
        ],
        ["7777"]
    ],
    "heading": null,
    "file": "207003.bufr"
}]