Utility Class: Common Calculations
A PhotonUtils
class with helpful common calculations is included within PhotonLib
to aid teams. This class contains two methods, calculateDistanceToTargetMeters()
/CalculateDistanceToTarget()
and estimateTargetTranslation2d()
/EstimateTargetTranslation()
(Java and C++ respectively).
Calculating Distance to Target
If your camera is at a fixed height on your robot and the height of the target is fixed, you can calculate the distance to the target based on your camera’s pitch and the pitch to the target.
}
@Override
public void teleopPeriodic() {
double forwardSpeed;
double rotationSpeed = xboxController.getLeftX();
if (xboxController.getAButton()) {
// Vision-alignment mode
// Query the latest result from PhotonVision
var result = camera.getLatestResult();
if (result.hasTargets()) {
// First calculate range
double range =
PhotonUtils.calculateDistanceToTargetMeters(
double rotationSpeed = xboxController.GetLeftX();
if (xboxController.GetAButton()) {
// Vision-alignment mode
// Query the latest result from PhotonVision
photonlib::PhotonPipelineResult result = camera.GetLatestResult();
if (result.HasTargets()) {
// First calculate range
Note
The C++ version of PhotonLib uses the Units library. For more information, see here.
Estimating Camera Translation to Target
You can get a translation to the target based on the distance to the target (calculated above) and angle to the target (yaw).
// Calculate a translation from the camera to the target.
Translation2d translation = PhotonUtils.estimateCameraToTargetTranslation(
distanceMeters, Rotation2d.fromDegrees(-target.getYaw()));
// Calculate a translation from the camera to the target.
frc::Translation2d translation = photonlib::PhotonUtils::EstimateCameraToTargetTranslationn(
distance, frc::Rotation2d(units::degree_t(-target.GetYaw())));
Note
We are negating the yaw from the camera from CV (computer vision) conventions to standard mathematical conventions. In standard mathematical conventions, as you turn counter-clockwise, angles become more positive.
Estimating Field Relative Pose
You can get your robot’s Pose2D
on the field using various camera data, target yaw, gyro angle, target pose, and camera position. This method estimates the target’s relative position using estimateCameraToTargetTranslation
(which uses pitch and yaw to estimate range and heading), and the robot’s gyro to estimate the rotation of the target.
// Calculate robot's field relative pose
Pose2D robotPose = PhotonUtils.estimateFieldToRobot(
kCameraHeight, kTargetHeight, kCameraPitch, kTargetPitch, Rotation2d.fromDegrees(-target.getYaw()), gyro.getRotation2d(), targetPose, cameraToRobot);
// Calculate robot's field relative pose
frc::Pose2D robotPose = photonlib::EstimateFieldToRobot(
kCameraHeight, kTargetHeight, kCameraPitch, kTargetPitch, frc::Rotation2d(units::degree_t(-target.GetYaw())), frc::Rotation2d(units::degree_t(gyro.GetRotation2d)), targetPose, cameraToRobot);