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.

Java

C++

// Constants
static final double kCameraHeight = 0.51; // meters
static final double kCameraPitch = 0.436; // radians
static final double kTargetHeight = 2.44; // meters

// Get distance to target.
double distanceMeters = PhotonUtils.calculateDistanceToTargetMeters(
  kCameraHeight, kTargetHeight, kCameraPitch, Math.toRadians(camera.getFirstTargetPitch());

#include <photonlib/PhotonUtils.h>
#include <units/length.h>
#include <units/angle.h>

// Constants
static constexpr auto kCameraHeight = 0.51_m;
static constexpr auto kCameraPitch = 0.436_rad;
static constexpr auto kTargetHeight = 2.44_m;

// Get distance to target.
units::meter_t distance = photonlib::PhotonUtils::CalculateDistanceToTarget(
  kCameraHeight, kTargetHeight, kCameraPitch, units::degree_t(camera.GetFirstTargetPitch()));

Note

The C++ version of PhotonLib uses the Units library. For more information, see here.

Estimating 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).

Java

C++

// Calculate a translation from the camera to the target.
Translation2d translation = PhotonUtils.estimateTargetTranslation2d(
  distanceMeters, Rotation2d.fromDegrees(-camera.getFirstTargetYaw()));

// Calculate a translation from the camera to the target.
frc::Translation2d translation = photonlib::PhotonUtils::EstimateTargetTranslation(
  distance, frc::Rotation2d(units::degree_t(-camera.GetFirstTargetYaw())));

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.