JSON Results Specification

Limelight's JSON results output is a collection of arrays containing targeting results. Separate arrays exist for retroreflective, fiducial, neural classifier, and neural detector results. JSON is human-readable and easy to parse in any language on any platform, so it is perfect for most use-cases.

The same JSON results output may be retrieved using the REST/HTTP, Websocket, and NetworkTables APIs.

Parsing this JSON output is incredibly easy with our FRC libraries.

Limelightlib has built-in functionality that parses the JSON Dump into a LimelightResults object.

https://github.com/LimelightVision/limelightlib-wpijava

https://github.com/LimelightVision/limelightlib-wpicpp

Every JSON result contains the following entries:

Key Name	Value Description
v	Validity indicator. 1 = valid targets, 0 = no valid targets
ts	Timestamp in milliseconds from boot (legacy).
ts_us	Timestamp in microseconds since application start.
ts_sys	System wall clock timestamp in microseconds since epoch.
ts_nt	NetworkTables server time in microseconds (0 if not connected).
fidx	Frame index (counter starting at 0).
tl	Targeting latency (milliseconds consumed by tracking loop this frame).
cl	Capture latency (milliseconds between the end of the exposure of the middle row to the beginning of the tracking loop).
pID	Current Pipeline index.
pTYPE	Current Pipeline Type e.g. "pipe_color".
tx	Horizontal Offset From Crosshair To Target (LL1: -27 degrees to 27 degrees / LL2: -29.8 to 29.8 degrees).
ty	Vertical Offset From Crosshair To Target (LL1: -20.5 degrees to 20.5 degrees / LL2: -24.85 to 24.85 degrees).
txnc	Horizontal Offset From Principal Pixel To Target (degrees).
tync	Vertical Offset From Principal Pixel To Target (degrees).
ta	Undistorted, normalized area of target (0-100).
focus_metric	Focus quality metric.
PythonOut	Output data from python SnapScript Pipelines (array of 8 doubles).
stdev_mt1	MT1 Standard Deviation [x, y, z, roll, pitch, yaw] (meters, degrees).
stdev_mt2	MT2 Standard Deviation [x, y, z, roll, pitch, yaw] (meters, degrees).
t6c_rs	Camera pose in robot space [x, y, z, roll, pitch, yaw] (meters, degrees).
botpose	Botpose (MegaTag): x,y,z, roll, pitch, yaw (meters, degrees).
botpose_wpired	Botpose (MegaTag, WPI Red driverstation): x,y,z, roll, pitch, yaw (meters, degrees).
botpose_wpiblue	Botpose (MegaTag, WPI Blue driverstation): x,y,z, roll, pitch, yaw (meters, degrees).
botpose_orb	Botpose (MegaTag2): x,y,z, roll, pitch, yaw (meters, degrees).
botpose_orb_wpired	Botpose (MegaTag2, WPI Red driverstation): x,y,z, roll, pitch, yaw (meters, degrees).
botpose_orb_wpiblue	Botpose (MegaTag2, WPI Blue driverstation): x,y,z, roll, pitch, yaw (meters, degrees).
botpose_tagcount	Number of tags used to compute botpose.
botpose_span	Max distance between tags used to compute botpose (meters).
botpose_avgdist	Average distance from camera to tags used to compute botpose (meters).
botpose_avgarea	Average area of tags used to compute botpose (percentage of image).
Retro	Color/Retroreflective pipeline results array.
Fiducial	AprilTag pipeline results array.
Detector	Neural Detector pipeline results array.
Classifier	Classifier pipeline results array.
Barcode	Barcode pipeline results array.
imgsrc	Image source setting value.
hwtype	Hardware type identifier.
uirefresh	1 if web UI needs refresh, 0 otherwise.
ignorent	1 if NetworkTables pipeline control is disabled, 0 otherwise.
imu	IMU data object. See IMU Object below.
hw	Hardware stats object. See Hardware Object below.
rewind	Rewind buffer stats object (supported hardware only). See Rewind Object below.

IMU Object

The "imu" object contains IMU sensor data:

Key Name	Value Description
quat	Orientation quaternion array [w, x, y, z]
yaw	Final fused yaw (degrees)
data	Raw IMU data array [roll, pitch, yaw, roll_rate, pitch_rate, yaw_rate, accel_x, accel_y, accel_z] (degrees, deg/s)

Hardware Object

The "hw" object contains hardware diagnostics:

Key Name	Value Description
temp	CPU temperature (Celsius)
cpu	CPU usage (percentage)
ram	RAM usage (percentage)
dfree	Disk free space (MB)
dtot	Disk total space (MB)
cid	Camera sensor ID
hailo	Hailo accelerator stats object (if present). See Hailo Object below.

Hailo Object

The "hailo" sub-object (inside "hw") contains Hailo accelerator info:

Key Name	Value Description
present	1 if Hailo accelerator detected, 0 otherwise
type	Hailo device type string
temp	Hailo temperature (Celsius)
power	Hailo power consumption (watts)
throttle	Throttle capability enabled

Rewind Object

The "rewind" object contains rewind buffer stats (supported hardware only):

Key Name	Value Description
enabled	1 if rewind recording is enabled, 0 if paused
storedSeconds	Seconds of video currently stored in buffer
frameCount	Number of frames in buffer
bufferUsage	Buffer usage (0.0 to 1.0)
flushing	1 if currently flushing to disk, 0 otherwise

Color/Retroreflective Results

The "Retro" array contains entries with the following structure:

Key Name	Value Description
t6c_ts	Camera Pose in target space as computed by solvepnp (x,y,z,rx,ry,rz)
t6r_fs	Robot Pose in field space as computed by solvepnp (x,y,z,rx,ry,rz)
t6r_ts	Robot Pose in target space as computed by solvepnp (x,y,z,rx,ry,rz)
t6t_cs	Target Pose in camera space as computed by solvepnp (x,y,z,rx,ry,rz)
t6t_rs	Target Pose in robot space as computed by solvepnp (x,y,z,rx,ry,rz)
ta	The size of the target as a percentage of the image (0-1)
tx	X-coordinate of the center of the target in degrees relative to crosshair. Positive-right, center-zero
tx_nocross	X-coordinate of the center of the target in degrees relative to principal piexel. Positive-right, center-zero
txp	X-coordinate of the center of the target in pixels relative to crosshair. Positive-right, center-zero
ty	Y-coordinate of the center of the target in degrees relative to crosshair. Positive-down, center-zero
ty_nocross	Y-coordinate of the center of the target in degrees relative to principal pixel. Positive-right, center-zero
typ	Y-coordinate of the center of the target in pixels relative to crosshair. Positive-down, center-zero
pts	Corners array (pixels) [x0,y0,x1,y1.....]. Must be enabled in output tab

Example JSON for Color / Retroreflective Pipelines

{
  "Barcode": [],
  "Classifier": [],
  "Detector": [],
  "Fiducial": [],
  "PythonOut": [],
  "Retro": [
    {
      "pts": [],
      "t6c_ts": [],
      "t6r_fs": [],
      "t6r_ts": [],
      "t6t_cs": [],
      "t6t_rs": [],
      "ta": 0.00531171215698123,
      "tx": -4.535492777705656,
      "tx_nocross": -4.428826910553056,
      "txp": 542.53076171875,
      "ty": -1.1722867231218714,
      "ty_nocross": -0.09285491974145543,
      "typ": 504.5538635253906
    },
    {
      "pts": [],
      "t6c_ts": [],
      "t6r_fs": [],
      "t6r_ts": [],
      "t6t_cs": [],
      "t6t_rs": [],
      "ta": 0.005779948551207781,
      "tx": 8.465099348209478,
      "tx_nocross": 8.571765215362078,
      "txp": 822.1087036132812,
      "ty": -2.524207730360601,
      "ty_nocross": -1.444775926980185,
      "typ": 533.6112060546875
    },
  ],
  "botpose": [
    0,
    0,
    0,
    0,
    0,
    0
  ],
  "botpose_avgarea": 0,
  "botpose_avgdist": 0,
  "botpose_orb": [
    0,
    0,
    0,
    0,
    0,
    0
  ],
  "botpose_orb_wpiblue": [
    0,
    0,
    0,
    0,
    0,
    0
  ],
  "botpose_orb_wpired": [
    0,
    0,
    0,
    0,
    0,
    0
  ],
  "botpose_span": 0,
  "botpose_tagcount": 0,
  "botpose_wpiblue": [
    0,
    0,
    0,
    0,
    0,
    0
  ],
  "botpose_wpired": [
    0,
    0,
    0,
    0,
    0,
    0
  ],
  "cl": 37.619998931884766,
  "fidx": 1234,
  "focus_metric": 0,
  "pID": 0,
  "pTYPE": "pipe_color",
  "stdev_mt1": [
    0,
    0,
    0,
    0,
    0,
    0
  ],
  "stdev_mt2": [
    0,
    0,
    0,
    0,
    0,
    0
  ],
  "t6c_rs": [
    0,
    0,
    0,
    0,
    0,
    0
  ],
  "ta": 0.39156023412942886,
  "tl": 22.64053726196289,
  "ts": 215248.979204,
  "ts_us": 215248979204,
  "ts_sys": 1705432800000000,
  "ts_nt": 12345678901234,
  "tx": -4.3848327488723555,
  "txnc": -4.278166881719756,
  "ty": -1.1144596937982527,
  "tync": -0.035027890417836716,
  "v": 1,
  "imgsrc": 0,
  "hwtype": 7,
  "uirefresh": 0,
  "ignorent": 0,
  "imu": {
    "quat": [1, 0, 0, 0],
    "yaw": 0,
    "data": [0, 0, 0, 0, 0, 0, 0, 0, 0]
  },
  "hw": {
    "temp": 57.9,
    "cpu": 45.2,
    "ram": 32.1,
    "dfree": 12500,
    "dtot": 28000,
    "cid": 9281,
    "hailo": {
      "present": 1,
      "type": "HAILO8L",
      "temp": 52.3,
      "power": 3.2,
      "throttle": 0
    }
  },
  "rewind": {
    "enabled": 1,
    "storedSeconds": 45.2,
    "frameCount": 1356,
    "bufferUsage": 0.35,
    "flushing": 0
  }
}

AprilTag/Fiducial Results

The "Fiducial" array contains entries with the following structure:

Key Name	Value Description
fID	Fiducial tag ID
fam	Fiducial Family (16H5C, 25H9C, 36H11C, etc)
pts	Return individual corner points. Must be enabled.
skew	Currently unused
t6c_ts	Camera Pose in target space as computed by this fiducial (x,y,z,pitch,yaw,roll) (meters, degrees)
t6r_fs	Robot Pose in field space as computed by this fiducial (x,y,z,pitch,yaw,roll) (meters, degrees)
t6r_fs_orb	Robot Pose in field space as computed by this fiducial (Megatag2) (x,y,z,pitch,yaw,roll) (meters, degrees)
t6r_ts	Robot Pose in target space as computed by this fiducial (x,y,z,pitch,yaw,roll) (meters, degrees)
t6t_cs	Target Pose in camera space as computed by this fiducial (x,y,z,pitch,yaw,roll) (meters, degrees)
t6t_rs	Target Pose in robot space as computed by this fiducial (x,y,z,pitch,yaw,roll) (meters, degrees)
ta	The size of the target as a percentage of the image (0-1)
tx	X-coordinate of the center of the target in degrees relative to crosshair. Positive-right, center-zero
tx_nocross	X-coordinate of the center of the target in degrees relative to principal piexel. Positive-right, center-zero
txp	X-coordinate of the center of the target in pixels relative to crosshair. Positive-right, center-zero
ty	Y-coordinate of the center of the target in degrees relative to crosshair. Positive-down, center-zero
ty_nocross	Y-coordinate of the center of the target in degrees relative to principal pixel. Positive-right, center-zero
typ	Y-coordinate of the center of the target in pixels relative to crosshair. Positive-down, center-zero
pts	Corners array (pixels) [x0,y0,x1,y1.....]. Must be enabled in output tab

Example JSON for AprilTag Pipelines

{
    "Classifier": [],
    "Detector": [],
    "Fiducial": [
    {
        "fID": 2,
        "fam": "16H5C",
        "pts": [],
        "skew": [],
        "t6c_ts": [
        0.33247368976801916,
        -0.05672695778305914,
        -2.5042031405987144,
        -4.680849607956358,
        -5.171154989721864,
        4.528697946312339
        ],
        "t6r_fs": [
        4.738896418276903,
        -1.5926603672041666,
        0.5194469577830592,
        4.522658587661256,
        4.258580454853879,
        5.5236539893713275
        ],
        "t6r_ts": [
        0.33247368976801916,
        -0.05672695778305914,
        -2.5042031405987144,
        -4.680849607956358,
        -5.171154989721864,
        4.528697946312339
        ],
        "t6t_cs": [
        -0.09991902572799474,
        -0.1234042720218289,
        2.5218203039582496,
        4.278368708252767,
        5.508508005282244,
        -4.1112864453027775
        ],
        "t6t_rs": [
        -0.09991902572799474,
        -0.1234042720218289,
        2.5218203039582496,
        4.278368708252767,
        5.508508005282244,
        -4.1112864453027775
        ],
        "ta": 0.005711808800697327,
        "tx": -2.0525293350219727,
        "txp": 149.4874725341797,
        "ty": 2.7294836044311523,
        "typ": 107.14710235595703
    }
    ],
    "Retro": [],
    "pID": 0,
    "tl": 19.78130340576172,
    "ts": 3284447.910569,
    "v": 1
}

Neural Detector Results

The "Detector" array contains entries with the following structure:

Key Name	Value Description
class	Human-readable class name string
classID	ClassID integer
conf	Confidence of the predicition
pts	Individual corner points as an array of [x,y] in pixels. Center-zero, positive right and down. Must be enabled.
ta	The size of the target as a percentage of the image (0-1)
tx	X-coordinate of the center of the target in degrees relative to crosshair. Positive-right, center-zero
tx_nocross	X-coordinate of the center of the target in degrees relative to principal piexel. Positive-right, center-zero
txp	X-coordinate of the center of the target in pixels relative to crosshair. Positive-right, center-zero
ty	Y-coordinate of the center of the target in degrees relative to crosshair. Positive-down, center-zero
ty_nocross	Y-coordinate of the center of the target in degrees relative to principal pixel. Positive-right, center-zero
typ	Y-coordinate of the center of the target in pixels relative to crosshair. Positive-down, center-zero
pts	Corners array (pixels) [x0,y0,x1,y1.....]. Must be enabled in output tab

Example JSON for Detector Pipelines

{
    "Classifier": [],
    "Detector": [
    {
        "class": "person",
        "classID": 0,
        "conf": 0.83984375,
        "pts": [],
        "ta": 0.2608712911605835,
        "tx": -2.45949649810791,
        "txp": 147.5,
        "ty": -10.066887855529785,
        "typ": 165.5
    }
    ],
    "Fiducial": [],
    "Retro": [],
    "pID": 0,
    "tl": 63.50614547729492,
    "ts": 4932985.266867,
    "v": 1
}

Neural Classifier Results

The "Classifier" array contains entries with the following structure:

Key Name	Value Description
class	Human-readable class name string
classID	ClassID integer
conf	Confidence of the predicition

Example JSON for Classifier Pipelines

{
    "Classifier": [
    {
        "class": "digital clock",
        "classID": 531,
        "conf": 0.16796875
    }
    ],
    "Detector": [],
    "Fiducial": [],
    "Retro": [],
    "pID": 0,
    "tl": 16.704740524291992,
    "ts": 4751332.7542280005,
    "v": 1
}

Barcode Results

The "Barcode" array contains entries with the following structure:

Key Name	Value Description
fam	Barcode Family e.g. "qr"
data	Decoded barcode data as string
ta	The size of the target as a percentage of the image (0-1)
tx	X-coordinate of the center of the target in degrees relative to crosshair. Positive-right, center-zero
tx_nocross	X-coordinate of the center of the target in degrees relative to principal piexel. Positive-right, center-zero
txp	X-coordinate of the center of the target in pixels relative to crosshair. Positive-right, center-zero
ty	Y-coordinate of the center of the target in degrees relative to crosshair. Positive-down, center-zero
ty_nocross	Y-coordinate of the center of the target in degrees relative to principal pixel. Positive-right, center-zero
typ	Y-coordinate of the center of the target in pixels relative to crosshair. Positive-down, center-zero
pts	Corners array (pixels) [x0,y0,x1,y1.....]. Must be enabled in output tab

Example JSON for Barcode Pipelines

{
    "Barcode": [
    {
        "fam": "QR",
        "data": "Hello, World!",
        "txp": 150.5,
        "typ": 120.75,
        "tx": -2.5,
        "ty": 1.8,
        "tx_nocross": -2.3,
        "ty_nocross": 2.0,
        "ta": 0.05,
        "pts": [[140, 110], [160, 110], [160, 130], [140, 130]]
    }
    ],
    "Classifier": [],
    "Detector": [],
    "Fiducial": [],
    "Retro": [],
    "pID": 0,
    "tl": 15.2,
    "ts": 4751332.7542280005,
    "v": 1
}

JSON Results Specification

IMU Object​

Hardware Object​

Hailo Object​

Rewind Object​

Color/Retroreflective Results​

AprilTag/Fiducial Results​

Neural Detector Results​

Neural Classifier Results​

Barcode Results​