Every LimelightHelpers method accepts a limelightName string that maps directly to the NetworkTables table name for that camera. You can run as many Limelight cameras as your robot’s network can support, each operating independently.
Naming your cameras
Configure each Limelight’s hostname in its web UI (Settings > Networking). Choose descriptive names that reflect each camera’s position on the robot:
Use a consistent naming convention like "limelight-front", "limelight-back", "limelight-left", "limelight-right". Avoid names with spaces. Shorter names reduce NetworkTables overhead.
// Each camera is addressed by its hostname
LimelightHelpers.PoseEstimate front =
LimelightHelpers.getBotPoseEstimate_wpiBlue_MegaTag2("limelight-front");
LimelightHelpers.PoseEstimate back =
LimelightHelpers.getBotPoseEstimate_wpiBlue_MegaTag2("limelight-back");
Camera pose calibration
Accurate camera pose calibration is critical for multi-camera localization. Even a few millimeters of error in the camera’s position on the robot will cause the two cameras to disagree about the robot’s location, degrading the fused estimate. Measure each camera’s offset from the robot’s origin carefully and verify with field tests.
robotInit()):
// Forward = positive X, Side = positive Y (left), Up = positive Z
// Roll, Pitch, Yaw in degrees
LimelightHelpers.setCameraPose_RobotSpace(
"limelight-front",
0.30, // 0.30 m forward of robot center
0.00, // centered left/right
0.50, // 0.50 m above ground
0.0, // roll
-30.0, // pitch (angled downward 30°)
0.0 // yaw (facing straight ahead)
);
LimelightHelpers.setCameraPose_RobotSpace(
"limelight-back",
-0.30, // 0.30 m behind robot center
0.00,
0.50,
0.0,
-30.0,
180.0 // yaw (facing backward)
);
MegaTag2 with multiple cameras
When using MegaTag2, call SetRobotOrientation() for each camera separately before reading its estimate:
double yaw = poseEstimator.getEstimatedPosition().getRotation().getDegrees();
LimelightHelpers.SetRobotOrientation("limelight-front", yaw, 0, 0, 0, 0, 0);
LimelightHelpers.SetRobotOrientation("limelight-back", yaw, 0, 0, 0, 0, 0);
LimelightHelpers.PoseEstimate front =
LimelightHelpers.getBotPoseEstimate_wpiBlue_MegaTag2("limelight-front");
LimelightHelpers.PoseEstimate back =
LimelightHelpers.getBotPoseEstimate_wpiBlue_MegaTag2("limelight-back");
Complete multi-camera robotPeriodic() pattern
@Override
public void robotPeriodic() {
// Update wheel odometry
poseEstimator.update(gyro.getRotation2d(), modulePositions);
double yaw = poseEstimator.getEstimatedPosition().getRotation().getDegrees();
boolean spinning = Math.abs(gyro.getRate()) > 720;
// Process each camera
processCameraEstimate("limelight-front", yaw, spinning);
processCameraEstimate("limelight-back", yaw, spinning);
}
private void processCameraEstimate(String name, double yaw, boolean spinning) {
LimelightHelpers.SetRobotOrientation(name, yaw, 0, 0, 0, 0, 0);
LimelightHelpers.PoseEstimate est =
LimelightHelpers.getBotPoseEstimate_wpiBlue_MegaTag2(name);
if (!LimelightHelpers.validPoseEstimate(est)) return;
if (spinning) return;
if (est.tagCount == 0) return;
// Scale standard deviations by distance — trust less when farther away
double stdDev = 0.5 + (est.avgTagDist * 0.1);
Matrix<N3, N1> stdDevs = VecBuilder.fill(stdDev, stdDev, 9999999);
poseEstimator.addVisionMeasurement(
est.pose,
est.timestampSeconds,
stdDevs
);
}
Choosing between competing estimates
When both cameras return a valid estimate, you can select the better one rather than blindly applying both:
LimelightHelpers.PoseEstimate bestEstimate = pickBestEstimate(front, back);
private LimelightHelpers.PoseEstimate pickBestEstimate(
LimelightHelpers.PoseEstimate a,
LimelightHelpers.PoseEstimate b) {
boolean aValid = LimelightHelpers.validPoseEstimate(a) && a.tagCount > 0;
boolean bValid = LimelightHelpers.validPoseEstimate(b) && b.tagCount > 0;
if (!aValid && !bValid) return null;
if (!aValid) return b;
if (!bValid) return a;
// Prefer more tags
if (a.tagCount != b.tagCount) {
return a.tagCount > b.tagCount ? a : b;
}
// Prefer lower ambiguity on the first tag
double aAmbiguity = a.rawFiducials.length > 0 ? a.rawFiducials[0].ambiguity : 1.0;
double bAmbiguity = b.rawFiducials.length > 0 ? b.rawFiducials[0].ambiguity : 1.0;
return aAmbiguity <= bAmbiguity ? a : b;
}
validPoseEstimate()
Use LimelightHelpers.validPoseEstimate(pose) as a quick null-safety check before accessing any field:
// Returns false if pose is null, rawFiducials is null, or rawFiducials is empty
if (LimelightHelpers.validPoseEstimate(est)) {
// safe to access est.pose, est.rawFiducials, etc.
}
Debugging with printPoseEstimate()
printPoseEstimate() prints a full summary to stdout: timestamp, latency, tag count, span, average distance, average area, and per-fiducial details including ambiguity.
LimelightHelpers.printPoseEstimate(front);
// Output example:
// Pose Estimate Information:
// Timestamp (Seconds): 245.312
// Latency: 22.500 ms
// Tag Count: 2
// Tag Span: 3.40 meters
// Average Tag Distance: 2.15 meters
// Average Tag Area: 4.20% of image
// Is MegaTag2: true
//
// Raw Fiducials Details:
// Fiducial #1:
// ID: 4
// TXNC: -3.20
// TYNC: 1.10
// TA: 5.20
// Distance to Camera: 2.10 meters
// Distance to Robot: 2.15 meters
// Ambiguity: 0.02
USB camera port forwarding
For Limelight cameras connected via USB (e.g., Limelight 3A or 3G), set up port forwarding during robotInit() so the web interface and video streams are accessible:
@Override
public void robotInit() {
// Limelight on USB index 0: ports 5800–5809 → 172.29.0.1
LimelightHelpers.setupPortForwardingUSB(0);
// Limelight on USB index 1: ports 5810–5819 → 172.29.1.1
LimelightHelpers.setupPortForwardingUSB(1);
}
roboRIO-TEAM-FRC.local:5801 for USB index 0, and :5811 for USB index 1.