LibEPN (Easy Pose Notation) is a Java library designed to provide an easy-to-use interface for 3D position and orientation. The library is heavily dependant on Quaternions, and makes use of the following dependencies:

• Apache Commons Math
• Efficient Java Matrix Library

I use this library in various personal and school projects relating to pose estimation, robotics, and computer vision.

Step 1. Add the RetryLife maven server to your build.gradle file:

repositories {
    maven { 
        name 'retrylife-release'
        url 'https://release.maven.retrylife.ca/' 
    }
}

Step 2. Add this library as a dependency:

dependencies {
    implementation 'ca.retrylife:easy-pose-notation:1.+'
    implementation 'ca.retrylife:easy-pose-notation:1.+:sources'
    implementation 'ca.retrylife:easy-pose-notation:1.+:javadoc'
}

The following should be noted when working with coordinates:

• alpha, beta, and gamma refer respectively to the Z, X and Y axes of rotation.
• The coordinate system assumes that:
  • If you are at (x: 0, y: 1, z: 0) facing (0,0,0), the Y axis will be coming "towards" you, X will be increasing to your left, and Z will be increasing towards the sky.
• All angles will increase to the left around any axis assuming you are in line with the axis, looking at (0,0,0)
• All coordinate and angle systems follow that of Google's device orientation specification, and the world frame coordinate system used by MIT's Drake.

The following is a basic usage example. See the JavaDoc for full API reference.

// Create a pose at (10,0,0) rotated around the Z axis to the left by 45 degrees
Pose p = new Pose(
    new SimpleMatrix(new double[][]{{10,0,0}}), 
    QuaternionUtil.quaternionFromEulerAngles(Math.toRadians(45), 0, 0)
);

// Print the pose's quaternion
System.out.println(p.getRotation());

// Print the pose's rotation as euler angles
System.out.println(p.getEulerRotation());

// Print the pose's position
System.out.println(p.getPosition());

// Print the pose's "surface normal
System.out.println(p.getNormal());

This library also contains a sub-library called EPN4FRC. This is a small binding between LibEPN and WPILib's Pose2d coordinate system for the FIRST Robotics Competition. EPN4FRC in-source documentation can be found here.

This library was heavily supported by the following sources:

• Wikipedia: Quaternions
• Wikipedia: Conversion between quaternions and Euler angles
• 3blue1brown: Visualizing Quaternions
• 3blue1brown: Quaternions and 3d rotation, explained interactively