PythonMessageDecoder.rst

Python-Based Message Decoder

Contents

• Creating a python-based decoder

.. sectionauthor:: Joseph S Motyka <jmotyka at aceinna.com>

Creating a python-based decoder

The first step to using the OpenIMU decoder and spooling tools, python-openimu, to properly decode an output message, is to define the message in the file openimu.json. For the “s1” message, the following is added to the file:

{
    "name": "s1",
    "description": "IMU Scaled-Sensor Output Message",
    "payload": [{
            "type": "uint32",
            "name": "timeCntr",
            "unit": "msec"
        },
        {
            "type": "double",
            "name": "time",
            "unit": "s"
        },
        {
            "type": "float",
            "name": "xAccel",
            "unit": "g"
        },
        {
            "type": "float",
            "name": "yAccel",
            "unit": "g"
        },
        {
            "type": "float",
            "name": "zAccel",
            "unit": "g"
        },
        {
            "type": "float",
            "name": "xRate",
            "unit": "deg/s"
        },
        {
            "type": "float",
            "name": "yRate",
            "unit": "deg/s"
        },
        {
            "type": "float",
            "name": "zRate",
            "unit": "deg/s"
        },
        {
            "type": "float",
            "name": "xMag",
            "unit": "G"
        },
        {
            "type": "float",
            "name": "yMag",
            "unit": "G"
        },
        {
            "type": "float",
            "name": "zMag",
            "unit": "G"
        },
        {
            "type": "float",
            "name": "temp",
            "unit": "degC"
        }
    ],
        "graphs": [{
            "name": "Acceleration",
            "units": "g",
            "xAxis": "Time (s)",
            "yAxes": ["xAccel", "yAccel", "zAccel"],
            "colors": ["#FF0000", "#00FF00", "#0000FF"],
            "yMax": 5
        },
        {
            "name": "Angular-Rate",
            "units": "deg/s",
            "xAxis": "Time (s)",
            "yAxes": ["xRate", "yRate", "zRate"],
            "colors": ["#FF0000", "#00FF00", "#0000FF"],
            "yMax": 200
        },
        {
            "name": "Magnetic-Field",
            "units": "G",
            "xAxis": "Time (s)",
            "yAxes": ["xMag", "yMag", "zMag"],
            "colors": ["#FF0000", "#00FF00", "#0000FF"],
            "yMax": 5
        },
        {
            "name": "Board-Temperature",
            "units": "degC",
            "xAxis": "Time (s)",
            "yAxes": ["temp"],
            "colors": ["#FF0000"],
            "yMax": 100
        }
    ]
}

This information tells the decoder the order of the output data in the serial message, its type (float, double, int, etc.), as well as the units associated with the data. It also defines how the data should be plotted, including axis-titles and colors.

Note

A useful tool to check if the json-file is properly formatted is found at: https://jsonlint.com