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name: robot-perception description: > Comprehensive best practices for robot perception systems covering cameras, LiDARs, depth sensors, IMUs, and multi-sensor setups. Use this skill when working with RGB image processing, depth maps, point clouds, sensor calibration (intrinsic, extrinsic, hand-eye), object detection, semantic segmentation, 3D reconstruction, visual servoing, or perception pipeline optimization. Trigger whenever the user mentions OpenCV, Open3D, PCL, RealSense, ZED, OAK-D, camera calibration, AprilTags, ArUco markers, stereo vision, RGBD, point cloud filtering, ICP registration, coordinate transforms, camera intrinsics, distortion correction, image undistortion, sensor streaming, frame synchronization, or any computer vision task in a robotics context. Also covers multi-camera rigs, time synchronization across sensors, perception latency budgets, and production deployment of perception pipelines.

Robot Perception Skill

When to Use This Skill

• Setting up and configuring camera, LiDAR, or depth sensors
• Building RGB, depth, or point cloud processing pipelines
• Calibrating cameras (intrinsic, extrinsic, hand-eye)
• Implementing object detection, segmentation, or tracking for robots
• Fusing data from multiple sensor modalities
• Streaming sensor data with proper threading and buffering
• Synchronizing multi-sensor rigs
• Deploying perception models on robot hardware (GPU, edge)
• Debugging perception failures (latency, dropped frames, misalignment)

Sensor Landscape

Sensor Types and Characteristics

Sensor Type        Output              Range       Rate     Best For
─────────────────────────────────────────────────────────────────────────
RGB Camera         (H,W,3) uint8       ∞           30-120Hz Object detection, tracking, visual servoing
Stereo Camera      (H,W,3)+(H,W,3)    0.3-20m     30-90Hz  Dense depth from passive stereo
Structured Light   (H,W) float + RGB   0.2-10m     30Hz     Indoor manipulation, short range
ToF Depth          (H,W) float + RGB   0.1-10m     30Hz     Indoor, medium range
LiDAR (spinning)   (N,3) or (N,4)     0.5-200m    10-20Hz  Outdoor navigation, mapping
LiDAR (solid-st.)  (N,3)              0.5-200m    10-30Hz  Automotive, outdoor
IMU                (6,) or (9,)        N/A         200-1kHz Orientation, motion estimation
Force/Torque       (6,) float          N/A         1kHz+    Contact detection, force control
Tactile            (H,W) or (N,3)      Contact     30-100Hz Grasp quality, texture
Event Camera       Events (x,y,t,p)    ∞           μs       High-speed tracking, HDR scenes

Common Sensor Hardware

Device             Type               SDK/Driver           ROS2 Package
──────────────────────────────────────────────────────────────────────────
Intel RealSense    Structured Light   pyrealsense2         realsense2_camera
Stereolabs ZED     Stereo + IMU       pyzed                zed_wrapper
Luxonis OAK-D      Stereo + Neural    depthai              depthai_ros
FLIR/Basler        Industrial RGB     PySpin/pypylon       spinnaker_camera_driver
Velodyne           Spinning LiDAR     velodyne_driver      velodyne
Ouster             Spinning LiDAR     ouster-sdk           ros2_ouster
Livox              Solid-state LiDAR  livox_sdk            livox_ros2_driver
USB Webcam         RGB                OpenCV VideoCapture  usb_cam / v4l2_camera

Camera Models and Calibration

Pinhole Camera Model

                    3D World Point (X, Y, Z)
                           |
                    [R | t] — Extrinsic (world → camera)
                           |
                    Camera Point (Xc, Yc, Zc)
                           |
                    K — Intrinsic (camera → pixel)
                           |
                    Pixel (u, v)

K = [ fx   0   cx ]      fx, fy = focal lengths (pixels)
    [  0  fy   cy ]      cx, cy = principal point
    [  0   0    1 ]

Projection:  [u, v, 1]^T = K @ [R | t] @ [X, Y, Z, 1]^T

Intrinsic Calibration

import cv2
import numpy as np
from pathlib import Path

class IntrinsicCalibrator:
    """Camera intrinsic calibration using checkerboard pattern"""

    def __init__(self, board_size=(9, 6), square_size_m=0.025):
        self.board_size = board_size
        self.square_size = square_size_m

        # Prepare object points (3D coordinates of checkerboard corners)
        self.objp = np.zeros((board_size[0] * board_size[1], 3), np.float32)
        self.objp[:, :2] = np.mgrid[
            0:board_size[0], 0:board_size[1]
        ].T.reshape(-1, 2) * square_size_m

    def collect_calibration_images(self, camera, num_images=30,
                                    min_coverage=0.6):
        """Collect calibration images with good spatial coverage.

        IMPORTANT: Move the board to cover all regions of the image,
        including corners and edges. Tilt the board at various angles.
        Bad coverage = bad calibration, especially at image edges.
        """
        obj_points = []
        img_points = []
        coverage_map = np.zeros((4, 4), dtype=int)  # Track board positions

        while len(obj_points) < num_images:
            frame = camera.capture()
            gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)

            found, corners = cv2.findChessboardCorners(
                gray, self.board_size,
                cv2.CALIB_CB_ADAPTIVE_THRESH |
                cv2.CALIB_CB_NORMALIZE_IMAGE |
                cv2.CALIB_CB_FAST_CHECK
            )

            if found:
                # Sub-pixel refinement — critical for accuracy
                criteria = (cv2.TERM_CRITERIA_EPS +
                           cv2.TERM_CRITERIA_MAX_ITER, 30, 0.001)
                corners = cv2.cornerSubPix(
                    gray, corners, (11, 11), (-1, -1), criteria)

                # Track coverage
                center = corners.mean(axis=0).flatten()
                grid_x = int(center[0] / gray.shape[1] * 4)
                grid_y = int(center[1] / gray.shape[0] * 4)
                grid_x = min(grid_x, 3)
                grid_y = min(grid_y, 3)
                coverage_map[grid_y, grid_x] += 1

                obj_points.append(self.objp)
                img_points.append(corners)

        coverage = (coverage_map > 0).sum() / coverage_map.size
        if coverage < min_coverage:
            print(f"WARNING: Only {coverage:.0%} coverage. "
                  f"Move board to uncovered regions.")

        return obj_points, img_points, gray.shape[::-1]

    def calibrate(self, obj_points, img_points, image_size):
        """Run calibration and return camera matrix + distortion coeffs"""
        ret, K, dist, rvecs, tvecs = cv2.calibrateCamera(
            obj_points, img_points, image_size, None, None)

        if ret > 1.0:
            print(f"WARNING: High reprojection error ({ret:.3f} px). "
                  f"Check image quality and board detection.")

        # Compute per-image reprojection errors
        errors = []
        for i in range(len(obj_points)):
            projected, _ = cv2.projectPoints(
                obj_points[i], rvecs[i], tvecs[i], K, dist)
            err = cv2.norm(img_points[i], projected, cv2.NORM_L2)
            err /= len(projected)
            errors.append(err)

        print(f"Calibration complete:")
        print(f"  RMS reprojection error: {ret:.4f} px")
        print(f"  Per-image errors: mean={np.mean(errors):.4f}, "
              f"max={np.max(errors):.4f}")
        print(f"  Focal length: fx={K[0,0]:.1f}, fy={K[1,1]:.1f}")
        print(f"  Principal point: cx={K[0,2]:.1f}, cy={K[1,2]:.1f}")

        return CalibrationResult(
            camera_matrix=K, dist_coeffs=dist,
            rms_error=ret, image_size=image_size)

    def save(self, result, path):
        """Save calibration to YAML (OpenCV-compatible format)"""
        fs = cv2.FileStorage(str(path), cv2.FILE_STORAGE_WRITE)
        fs.write("camera_matrix", result.camera_matrix)
        fs.write("dist_coeffs", result.dist_coeffs)
        fs.write("image_width", result.image_size[0])
        fs.write("image_height", result.image_size[1])
        fs.write("rms_error", result.rms_error)
        fs.release()

    @staticmethod
    def load(path):
        """Load calibration from YAML"""
        fs = cv2.FileStorage(str(path), cv2.FILE_STORAGE_READ)
        K = fs.getNode("camera_matrix").mat()
        dist = fs.getNode("dist_coeffs").mat()
        w = int(fs.getNode("image_width").real())
        h = int(fs.getNode("image_height").real())
        fs.release()
        return CalibrationResult(
            camera_matrix=K, dist_coeffs=dist,
            image_size=(w, h), rms_error=0.0)

Extrinsic Calibration (Camera-to-Camera, Camera-to-LiDAR)

class ExtrinsicCalibrator:
    """Compute transform between two sensors using shared targets"""

    def calibrate_stereo(self, calib_left, calib_right,
                          obj_points, img_points_left, img_points_right,
                          image_size):
        """Stereo calibration: find relative pose between two cameras"""
        ret, K1, d1, K2, d2, R, T, E, F = cv2.stereoCalibrate(
            obj_points, img_points_left, img_points_right,
            calib_left.camera_matrix, calib_left.dist_coeffs,
            calib_right.camera_matrix, calib_right.dist_coeffs,
            image_size,
            flags=cv2.CALIB_FIX_INTRINSIC  # Use pre-calibrated intrinsics
        )

        print(f"Stereo calibration RMS: {ret:.4f} px")
        print(f"Baseline: {np.linalg.norm(T):.4f} m")

        return StereoCalibration(R=R, T=T, E=E, F=F, rms_error=ret)

    def calibrate_camera_to_lidar(self, camera_points_2d,
                                    lidar_points_3d, K, dist):
        """Find camera-to-LiDAR transform using corresponding points.

        Use a calibration target visible to both sensors (e.g.,
        checkerboard with reflective tape corners).
        """
        # PnP: find pose of 3D points relative to camera
        success, rvec, tvec = cv2.solvePnP(
            lidar_points_3d, camera_points_2d, K, dist,
            flags=cv2.SOLVEPNP_ITERATIVE
        )

        if not success:
            raise CalibrationError("PnP failed — check point correspondences")

        R, _ = cv2.Rodrigues(rvec)
        T_camera_lidar = np.eye(4)
        T_camera_lidar[:3, :3] = R
        T_camera_lidar[:3, 3] = tvec.flatten()

        # Verify by reprojecting
        projected, _ = cv2.projectPoints(
            lidar_points_3d, rvec, tvec, K, dist)
        error = np.mean(np.linalg.norm(
            camera_points_2d - projected.reshape(-1, 2), axis=1))
        print(f"Camera-LiDAR reprojection error: {error:.2f} px")

        return T_camera_lidar

Hand-Eye Calibration (Camera-to-Robot)

class HandEyeCalibrator:
    """Solve AX = XB for camera mounted on robot end-effector (eye-in-hand)
    or camera mounted on a fixed base (eye-to-hand).

    Requires moving the robot to multiple poses while observing a
    fixed calibration target.
    """

    def __init__(self, K, dist, board_size=(9, 6), square_size=0.025):
        self.K = K
        self.dist = dist
        self.board_size = board_size
        self.square_size = square_size
        self.objp = np.zeros((board_size[0] * board_size[1], 3), np.float32)
        self.objp[:, :2] = np.mgrid[
            0:board_size[0], 0:board_size[1]
        ].T.reshape(-1, 2) * square_size

    def collect_poses(self, camera, robot, num_poses=20):
        """Collect camera-target and robot poses at multiple configurations.

        IMPORTANT: Move to diverse robot orientations. At least 3 different
        rotation axes. Pure translations are NOT sufficient.
        """
        R_gripper2base = []
        t_gripper2base = []
        R_target2cam = []
        t_target2cam = []

        for i in range(num_poses):
            input(f"Move robot to pose {i+1}/{num_poses}, press Enter.