Logging

class ULog

Class to handle the logging of data to a file in the ULog data format (https://docs.px4.io/main/en/dev_log/ulog_file_format.html). The interface is relatively simple. The user instantiates the object, runs the init() member function once, and then repeatedly calls the write_msg() member function to record the data to a file. The user can then use the px4tools python package to read the data from the file (typically it is converted to a CSV file). To increase the performance of the logging, the interaction with the file system is done in a separate thread. This way, the control thread doesn’t get backed up with I/O flushing.

Public Functions

ULog() = default

Construct a new ULog object.

~ULog()

Destroy the ULog object.

int init(const std::filesystem::path &log_folder)

Initialize the ULog object. This function must be called before any other member functions. It creates the file, writes the header, and starts the logging thread. The created file is called logger.ulog, and it placed in the directory provided.

Parameters:

log_filename – The name of the ULog file to create

Returns:

int 0 if successful, -1 otherwise

void write_msg(const ULogMsg &data)

Writes a generic ULogMsg to the log file. It serializes the data, then adds it to a queue to be written to the file. The queue is then flushed to the file in the logging thread.

Parameters:

data – The ULogMsg to write to the file

Public Static Functions

static std::filesystem::path generate_incremented_run_dir(const std::filesystem::path &log_folder)

Creates a directory for logging data for a given run. This is run with a very simple naming scheme, where the directory is named run<number>, where <number> is the first number that doesn’t already exist. The date or time is not used because the hardware usually doesn’t have a clock that is synchronized with local time.

Parameters:

log_folder – The base folder to create the run directory in

Returns:

std::filesystem::path The path to the created directory

struct ULogMsg

Base class for all ULog data structs. This sets the interface for how ULog data is processed to store on disk.

Subclassed by flyMS::ULogFlightMsg, flyMS::ULogGpsMsg, flyMS::ULogPosCntrlMsg

struct ULogFlightMsg : public flyMS::ULogMsg

Data struct for storing metrics that are used to evaluate the performance of the flight controller. This includes the system’s state, sensor data, setpoints, and control effort (motor commands) This struct inherits from ULogMsg and is used to write to the ULog file.

struct ULogFlightMsgData

The data fields that are recorded for the ULogFlightMsg. This struct is in serializable format.

struct ULogGpsMsg : public flyMS::ULogMsg

Data struct for storing GPS data. This struct inherits from ULogMsg and is used to write to the ULog file. It contains the recorded GPS LLA data.

struct ULogGpsMsgData

struct ULogPosCntrlMsg : public flyMS::ULogMsg

Data struct for storing the position and velocity of the vehicle. This struct inherits from ULogMsg and is used to write to the ULog file. This struct is only used when the flyMS system is receiving position and velocity data from an external source (e.g. VIO). It records here to show it’s consistency with the rest of the flyMS data.

struct ULogPosCntrlMsgData

The data fields that are recorded for the ULogPosCntrlMsg. This struct is in serializable format.