View source for Khepera III Toolbox/The Toolbox/Modules/odometry track

The ''odometry_track'' module implements the [[w:Odometry|odometry]] equations for a differential-drive vehicle and allows to track the robot's position (<math>x</math>, <math>y</math>, <math>\theta</math>) over time.
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== Synopsis ==

<syntaxhighlight lang="c">
// Instantiate a track structure
struct sOdometryTrack ot;

// Initialize the module
odometry_track_init();

// Start tracking and set initial position
odometry_track_start(&ot);
ot.result.x = 0;
ot.result.y = 0;
ot.result.theta = 0;

// Main loop
while (1) {
    ...

    // Call this frequently to update the position estimate
    odometry_track_step(&ot);
    ... = ot.result.x;
    ... = ot.result.y;
    ... = ot.result.theta;

    ...
}
</syntaxhighlight>

== Description ==

'''odometry_track_start''' sets up a ''sOdometryTrack'' structure and reads the odometry calibration values from ''/etc/khepera/odometry''. If that file is not available (or does not contain a valid configuration), default values are used. After calling this function, the initial position can be changed by modifying the ''result'' fields of the structure. '''odometry_track_start''' also reads the current motor positions and should therefore be called immediately before entering the main loop.

Inside the main loop, '''odometry_track_step''' is called to read the new motor positions and update the position estimate in the ''result'' fields.

== Calibration ==

The default calibration values should give acceptable results on most Khepera III robots. Through a [[Khepera III Toolbox/Examples/odometry_calibration|calibration procedure]], the precision can be significantly improved, however.

== Providing Motor Positions from Other Sources ==

The functions mentioned above read the motor positions automatically with the ''khepera3_drive_getposition'' function. If this is not desired, the functions '''odometry_track_start_pos''' and '''odometry_track_step_pos''' can be used.

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