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LimelightLib uses WPILib’s NetworkTables to communicate with Limelight cameras over the robot network. Every public method in LimelightHelpers takes a limelightName string parameter that maps directly to the NetworkTables table name.

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Camera naming

Pass the name you configured in the Limelight web UI — for example, "limelight", "limelight-front", or "limelight-back". Passing "" or null defaults to "limelight": 
// From LimelightHelpers.java
static final String sanitizeName(String name) {
    if ("".equals(name) || name == null) {
        return "limelight";
    }
    return name;
}
When using multiple cameras, always pass the full hostname you assigned in the Limelight web UI (e.g., "limelight-front", "limelight-back"). This maps directly to the NetworkTables table name and keeps data from each camera separate.

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Key NetworkTables entries

The library reads and writes specific NT entries on each camera’s table. The entries below are the most commonly used.

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Read entries

EntryTypeDescription
tvdoubleTarget valid. 1.0 = has a target, 0.0 = no target
txdoubleHorizontal offset from crosshair to target, in degrees
tydoubleVertical offset from crosshair to target, in degrees
tadoubleTarget area as a percentage of the image (0–100)
botpose_wpibluedouble[]Robot pose array in WPILib Blue Alliance coordinates
botpose_wpireddouble[]Robot pose array in WPILib Red Alliance coordinates
botpose_orb_wpibluedouble[]MegaTag2 pose array in Blue Alliance coordinates
botpose_orb_wpireddouble[]MegaTag2 pose array in Red Alliance coordinates
jsonstringFull JSON results dump — all targets, poses, and metadata
imudouble[]IMU data array: [robotYaw, roll, pitch, yaw, gyroX, gyroY, gyroZ, accelX, accelY, accelZ]
hbdoubleHeartbeat counter — increments once per frame
rawfiducialsdouble[]Raw AprilTag/fiducial detection array (7 values per tag)
rawdetectionsdouble[]Raw neural detector results (12 values per detection)
rawtargetsdouble[]Raw target contour results (3 values per contour)

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Write entries

EntryTypeDescription
pipelinedoubleActive pipeline index (0–9)
ledModedoubleLED mode: 0 = pipeline control, 1 = off, 2 = blink, 3 = on
streamdoubleStream mode: 0 = standard, 1 = PiP main, 2 = PiP secondary
cropdouble[]Camera crop window: [xMin, xMax, yMin, yMax] (–1 to 1)
robot_orientation_setdouble[]Robot orientation for MegaTag2: [yaw, yawRate, pitch, pitchRate, roll, rollRate]

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Entry caching

The library caches DoubleArrayEntry objects in a ConcurrentHashMap keyed by "tableName/entryName". Entries are created once on first access and reused on every subsequent call, which avoids the overhead of repeated NT lookups: 
private static final Map<String, DoubleArrayEntry> doubleArrayEntries = new ConcurrentHashMap<>();

public static DoubleArrayEntry getLimelightDoubleArrayEntry(String tableName, String entryName) {
    String key = tableName + "/" + entryName;
    return doubleArrayEntries.computeIfAbsent(key, k -> {
        NetworkTable table = getLimelightNTTable(tableName);
        return table.getDoubleArrayTopic(entryName).getEntry(new double[0]);
    });
}
This is used internally for all botpose and PoseEstimate reads.

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Flushing

LimelightHelpers.Flush() calls NetworkTableInstance.getDefault().flush() to force queued writes to be sent immediately. The library calls this automatically inside SetRobotOrientation() to ensure the camera receives the latest robot heading before the next MegaTag2 solve: 
public static void Flush() {
    NetworkTableInstance.getDefault().flush();
}
If you are calling SetRobotOrientation() at high frequency and do not want to flush on every call, use SetRobotOrientation_NoFlush() instead and flush manually at the end of your control loop.

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Using LimelightHelpers vs. raw NetworkTables

You can read from NetworkTables directly, but LimelightHelpers handles name sanitization, type defaults, and entry caching for you. 
// Reads "tx" from the "limelight-front" table
double tx = LimelightHelpers.getTX("limelight-front");

// Reads "tv" and returns a boolean
boolean hasTarget = LimelightHelpers.getTV("limelight-front");

// Writes the pipeline index
LimelightHelpers.setPipelineIndex("limelight-front", 2);

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