Retroreflective and color pipelines are Limelight’s classic targeting modes. They identify high-contrast targets (retroreflective tape, colored objects) and return angular offsets and area for each detected contour.
Core targeting values
These are the primary values available on every frame from a retroreflective or color pipeline:
| Method | Returns | Description |
|---|
getTV(name) | boolean | true if the camera sees a valid target |
getTX(name) | double | Horizontal offset from crosshair to target in degrees |
getTY(name) | double | Vertical offset from crosshair to target in degrees |
getTXNC(name) | double | Horizontal offset from the principal pixel in degrees |
getTYNC(name) | double | Vertical offset from the principal pixel in degrees |
getTA(name) | double | Target area as a percentage of the image (0–100%) |
boolean hasTarget = LimelightHelpers.getTV("limelight");
double tx = LimelightHelpers.getTX("limelight");
double ty = LimelightHelpers.getTY("limelight");
double txnc = LimelightHelpers.getTXNC("limelight");
double tync = LimelightHelpers.getTYNC("limelight");
double ta = LimelightHelpers.getTA("limelight");
tx/ty are measured from the adjustable crosshair you set in the Limelight web UI. txnc/tync are measured from the optical principal pixel — the most accurate 2D measurement when using a calibrated camera. Use txnc/tync when you need the best angular accuracy and don’t rely on a specific crosshair position.
tx range is approximately −29.8° to +29.8° for most Limelight cameras, though this depends on the camera model and lens.
Additional target data
Target color
Returns the average BGR (Blue-Green-Red) color of the pixels under the crosshair region:
double[] color = LimelightHelpers.getTargetColor("limelight");
double blue = color[0];
double green = color[1];
double red = color[2];
Multiple contour results
getRawTargets() returns up to 3 contour results directly from NetworkTables (no JSON parse):
LimelightHelpers.RawTarget[] targets =
LimelightHelpers.getRawTargets("limelight");
for (LimelightHelpers.RawTarget t : targets) {
System.out.printf("txnc=%.1f tync=%.1f ta=%.2f%n",
t.txnc, t.tync, t.ta);
}
Corner coordinates
Returns the corner points of the detected contour(s) as a flat [x0, y0, x1, y1, ...] array. Requires Send Contours to be enabled in the Limelight Output tab.
double[] corners = LimelightHelpers.getCornerCoordinates("limelight");
// corners[0] = x of first corner, corners[1] = y of first corner, etc.
Full results via JSON
For 3D pose data and additional per-target fields, parse the JSON output:
LimelightHelpers.LimelightResults results =
LimelightHelpers.getLatestResults("limelight");
for (LimelightHelpers.LimelightTarget_Retro t : results.targets_Retro) {
System.out.printf("tx=%.1f ty=%.1f ta=%.2f skew=%.1f%n",
t.tx, t.ty, t.ta, t.ts);
// 3D pose transforms
Pose3d robotInField = t.getRobotPose_FieldSpace();
Pose3d targetInCam = t.getTargetPose_CameraSpace();
Pose3d targetInRobot = t.getTargetPose_RobotSpace();
Pose3d camInTarget = t.getCameraPose_TargetSpace();
}
LimelightTarget_Retro fields:
| Field / Method | Description |
|---|
ta | Target area as % of image |
tx / ty | Angular offset from crosshair in degrees |
tx_pixels / ty_pixels | Offset in pixels |
tx_nocrosshair / ty_nocrosshair | Offset from principal pixel in degrees |
ts | Target skew in degrees |
getCameraPose_TargetSpace() | Camera pose relative to the target (3D) |
getRobotPose_FieldSpace() | Robot pose in field coordinates (3D) |
getTargetPose_CameraSpace() | Target pose relative to camera (3D) |
getTargetPose_RobotSpace() | Target pose relative to robot (3D) |
Aim-and-drive example
A common use case is steering the robot toward a target using getTX() as a proportional error signal, and estimating distance using getTY() or getTA().
@Override
public void teleopPeriodic() {
if (!LimelightHelpers.getTV("limelight")) {
// No target — stop or continue driving
drive.arcadeDrive(0, 0);
return;
}
double tx = LimelightHelpers.getTX("limelight");
double ty = LimelightHelpers.getTY("limelight");
double ta = LimelightHelpers.getTA("limelight");
// Proportional steering: tx drives the turn correction
double kP_steer = 0.03;
double steerCorrection = tx * kP_steer;
// Use ta as a proximity estimate — stop when target is "close enough"
boolean atTarget = ta > 10.0; // target fills >10% of image
if (!atTarget) {
double driveSpeed = 0.4;
drive.arcadeDrive(driveSpeed, steerCorrection);
} else {
drive.arcadeDrive(0, 0);
}
// ty can be used to estimate distance via the fixed-target formula:
// distance = (targetHeightMeters - cameraHeightMeters)
// / tan(cameraMountAngleDegrees + ty * PI/180)
}
Barcode detection
Limelight can decode QR codes, Data Matrix, and other 2D barcodes.
Raw barcode strings
String[] barcodes = LimelightHelpers.getRawBarcodeData("limelight");
for (String barcode : barcodes) {
System.out.println("Decoded: " + barcode);
}
Full barcode results via JSON
LimelightHelpers.LimelightResults results =
LimelightHelpers.getLatestResults("limelight");
for (LimelightHelpers.LimelightTarget_Barcode b : results.targets_Barcode) {
System.out.printf(
"Family: %s Data: %s tx=%.1f ty=%.1f ta=%.2f%n",
b.family, b.data, b.tx, b.ty, b.ta
);
// b.corners contains the corner coordinates of the barcode
}
LimelightTarget_Barcode fields:
| Field | Description |
|---|
family | Barcode type (e.g., "QR", "DataMatrix") |
data | Decoded content as a string |
tx / ty | Angular offset in degrees |
ta | Target area as % of image |
corners | 2D array of corner coordinates double[][] |