Lesson 12.2: Extracting Real-time Yaw Data using the AngleUnit Class

The Three Rotation Axes

The IMU tracks rotation along three distinct axes. Yaw describes rotation around the vertical axis -- this is the robot turning left or right on the field, which is what most navigation code cares about. Pitch describes rotation around the side-to-side axis, meaning the robot tilting forward or backward. Roll describes rotation around the front-to-back axis, meaning the robot leaning left or right. Lesson 12.4 covers pitch and roll for tip detection. This lesson focuses entirely on Yaw.

A critical detail: the IMU measures Yaw as the accumulated rotation from wherever the robot was pointing when resetYaw() was last called, or from the orientation at power-on if it was never called. The IMU does not know which direction is "toward the opposing alliance wall." What it knows is how many degrees the robot has rotated since the reference point was established. This relative nature is important to keep in mind when designing autonomous routines.

Reading Yaw with AngleUnit

The primary method for reading all three rotation angles simultaneously is imu.getRobotYawPitchRollAngles(). This returns a YawPitchRollAngles object. From that object, you call getYaw(AngleUnit) and pass in the unit you want the value expressed in.

The AngleUnit enum has two relevant values: DEGREES and RADIANS. Choosing degrees gives you a value between -180 and 180, where positive values represent counterclockwise rotation and negative values represent clockwise rotation as viewed from above. Choosing radians gives you the equivalent range from -π to π.

The SDK handles normalization automatically. If the robot spins multiple full revolutions, getYaw() will never return a value outside the -180 to 180 range. There is no need to implement your own wraparound logic when reading the angle.

The reason the method exists as a separate call from getYaw(AngleUnit.DEGREES) on the angles object -- rather than as a direct call on the imu -- is that getRobotYawPitchRollAngles() takes one snapshot of all three angles at the same instant. Calling it once and then reading individual axes from the result is slightly more consistent than calling separate methods multiple times, since the second call might capture a slightly different physical orientation than the first.

Annotated Code

package org.firstinspires.ftc.teamcode;

import com.qualcomm.robotcore.eventloop.opmode.OpMode;
import com.qualcomm.robotcore.eventloop.opmode.TeleOp;
import com.qualcomm.robotcore.hardware.IMU;
import com.qualcomm.hardware.rev.RevHubOrientationOnRobot;
import org.firstinspires.ftc.robotcore.external.navigation.AngleUnit;
import org.firstinspires.ftc.robotcore.external.navigation.YawPitchRollAngles;

@TeleOp(name="Yaw_Data_Demo")
public class YawDataDemo extends OpMode {

    private IMU imu;

    @Override
    public void init() {
        imu = hardwareMap.get(IMU.class, "imu");

        RevHubOrientationOnRobot orientation = new RevHubOrientationOnRobot(
            RevHubOrientationOnRobot.LogoFacingDirection.UP,
            RevHubOrientationOnRobot.UsbFacingDirection.FORWARD
        );
        imu.initialize(new IMU.Parameters(orientation));

        telemetry.addData("IMU", "Ready");
    }

    @Override
    public void loop() {
        // Take a single snapshot of all three rotation axes
        YawPitchRollAngles angles = imu.getRobotYawPitchRollAngles();

        // Extract Yaw specifically in degrees (-180 to 180)
        double yawDegrees = angles.getYaw(AngleUnit.DEGREES);

        // Extract the same value in radians if needed for math (-PI to PI)
        double yawRadians = angles.getYaw(AngleUnit.RADIANS);

        telemetry.addData("Yaw (degrees)", "%.2f", yawDegrees);
        telemetry.addData("Yaw (radians)", "%.4f", yawRadians);
        telemetry.update();
    }
}

Fill-in-the-Blank Practice

The method called on the IMU object to retrieve all three rotation axes at once is imu.__________().
To receive the heading as a value normalized between -180 and 180, pass AngleUnit.__________ to getYaw().
Rotation around the vertical axis, representing the robot turning left or right, is called __________.

Show answers

getRobotYawPitchRollAngles()
DEGREES
Yaw

Template Challenge

Robot Scenario: Create a TeleOp that reads the robot's current heading in degrees and displays it on the Driver Station. Also display whether the robot is currently pointed within 10 degrees of its starting heading (a boolean called isAligned). Assume the Hub is mounted flat with logo up and USB ports facing forward.

package org.firstinspires.ftc.teamcode;

import com.qualcomm.robotcore.eventloop.opmode.OpMode;
import com.qualcomm.robotcore.eventloop.opmode.TeleOp;
import com.qualcomm.robotcore.hardware.IMU;
import com.qualcomm.hardware.rev.RevHubOrientationOnRobot;
import org.firstinspires.ftc.robotcore.external.navigation.AngleUnit;

@TeleOp(name="Heading_Display_Challenge")
public class HeadingDisplay extends OpMode {

    private IMU imu;

    @Override
    public void init() {
        imu = hardwareMap.get(IMU.class, "imu");

        // INSERT CODE HERE: Initialize the IMU with logo UP and USB FORWARD

        telemetry.addData("IMU", "Ready");
    }

    @Override
    public void loop() {
        // INSERT CODE HERE: Read current yaw in degrees

        // INSERT CODE HERE: Compute isAligned -- true if Math.abs(yaw) < 10.0

        // INSERT CODE HERE: Display both values via telemetry
    }
}

Show answer

@Override
public void init() {
    imu = hardwareMap.get(IMU.class, "imu");

    RevHubOrientationOnRobot orientation = new RevHubOrientationOnRobot(
        RevHubOrientationOnRobot.LogoFacingDirection.UP,
        RevHubOrientationOnRobot.UsbFacingDirection.FORWARD
    );
    imu.initialize(new IMU.Parameters(orientation));

    telemetry.addData("IMU", "Ready");
}

@Override
public void loop() {
    double yaw = imu.getRobotYawPitchRollAngles().getYaw(AngleUnit.DEGREES);

    boolean isAligned = Math.abs(yaw) < 10.0;

    telemetry.addData("Heading (deg)", "%.2f", yaw);
    telemetry.addData("Aligned",       isAligned);
    telemetry.update();
}

Ready to move on?

The Three Rotation Axes​

Reading Yaw with AngleUnit​

Annotated Code​

Fill-in-the-Blank Practice​

Template Challenge​

The Three Rotation Axes

Reading Yaw with AngleUnit

Annotated Code

Fill-in-the-Blank Practice

Template Challenge