Localizers

Hermes supports many localization systems!

This guide will not attempt to suggest which localizer you use; there are many resources available for that.

What is a localizer?

A localizer is an object that provides the robot's position, orientation, and velocity in the field.

The most basic localizer is the drive localizer, which uses the encoders on your drive motors to determine the robot's position and orientation. However, many robots use additional sensors, such as deadwheel encoders, IMUs, or optical odometry, to improve localization accuracy.

The Localizer interface in Hermes provides a common API for all localizers, and has two properties and one method:

• pose: Pose2d (mutable): the robot's position and orientation in the field
• vel: PoseVelocity2d (read-only): the robot's velocity in the field
• update(): PoseVelocity2d: updates the localizer's pose and returns the robot's velocity

For Java users, the pose property is translated to Pose2d getPose() and void setPose(Pose2d pose) methods, and the vel property is translated to the PoseVelocity2d getVel() method.

Built-in Localizers

Hermes automatically detects which localizer your robot is using based on your hardware configuration!

Drive Localizers

MecanumDriveLocalizer and TankLocalizer use the encoders on your drive motors to determine the robot's position and orientation.

Two-Deadwheel Localizer

TwoDeadWheelLocalizer is for robots with two deadwheel pods (one parallel and one perpendicular to the robot's forward direction). Do not use this if you have the Pinpoint localization system.

Three-Deadwheel Localizer

ThreeDeadWheelLocalizer is for robots with three deadwheel pods (two parallel and one perpendicular to the robot's forward direction).

Pinpoint Localizer

PinpointLocalizer is for the goBILDA Pinpoint localization system with two deadwheel pods.

OTOS Localizer

OTOSLocalizer is for the SparkFun Optical Odometry (OTOS) system.

Custom Localizers

If you want to create a custom localizer, you can implement the Localizer interface and provide your own implementation of the properties and method described above:

KotlinJava

class CustomLocalizer : Localizer {
    override var pose: Pose2d = Pose2d.zero

    override var vel = PoseVelocity2d.zero
        private set

    override fun update(): PoseVelocity2d {
        pose = // calculate new pose
        vel = // calculate velocity
        return vel
    }
}

Note that we create both pose and vel as mutable properties, despite being read-only in the interface. This means that we can update both the pose and vel properties internally in the update method, but only pose can be set externally.

public class CustomLocalizer implements Localizer {
    private Pose2d pose = Pose2d.zero();
    private PoseVelocity2d vel = PoseVelocity2d.zero();

    @Override
    public Pose2d getPose() {
        return pose;
    }

    @Override
    public void setPose(Pose2d pose) {
        this.pose = pose;
    }

    @Override
    public PoseVelocity2d getVel() {
        return vel;
    }

    @Override
    public PoseVelocity2d update() {
        pose = // calculate new pose
        vel = // calculate velocity
        return vel;
    }
}