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Pose Estimation for Drones

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Pose Estimation for Drones

Pose estimation identifies human body keypoints from drone footage—enabling activity recognition, crowd analysis, and search-and-rescue operations. This tutorial covers the architectures for accurate aerial human pose estimation.

Aerial Pose Estimation Pipeline

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Drone pose estimation faces unique challenges: small subjects, extreme viewpoints, and motion blur.

Drone Human Pose Estimation

InputDrone ViewDetectPerson DetectorYOLOv8-PoseHeatmapKeypoint Prediction17 keypointsSkeletonAssemblyConnected limbsClassifyAction RecognitionWalking 90%Running 75%Standing 60%Sitting 45%Output• Keypoints• Skeleton• Action• ConfidenceTrack ID

COCO Keypoint Format (17 Points)

Keypoints:0: Nose1: Left Eye2: Right Eye3: Left Ear4: Right Ear5: Left Shoulder6: Right Shoulder7: Left Elbow8: Right Elbow9: Left Wrist10: Right Wrist11: Left Hip12: Right Hip13: Left Knee14: Right Knee15: Left Ankle16: Right AnkleAerial Challenges:📏Small scale (5-20px persons)🔄Top-down viewpoint💨Motion blur👥Crowd occlusion🎯Low resolution details
Architecture Diagram

**Real-world analogy:** Pose estimation from a drone is like watching people from a second-story window. You can see their overall posture and movement, but fine details like facial expressions are harder to distinguish. The challenge is reconstructing 3D body poses from these overhead 2D views.

Keypoint Detection

python
from dataclasses import dataclass
from typing import List, Tuple, Optional

@dataclass
class Keypoint:
    """Single body keypoint."""
    x: float
    y: float
    confidence: float
    keypoint_id: int

@dataclass
class Pose:
    """Complete human pose."""
    keypoints: List[Keypoint]
    bbox: Tuple[int, int, int, int]
    person_id: Optional[int] = None
    action: Optional[str] = None

class AerialPoseEstimator:
    """Pose estimation optimized for drone (aerial) views."""

    # COCO keypoint connections for skeleton
    SKELETON = [
        (0, 1), (0, 2), (1, 3), (2, 4),  # Head
        (5, 6),  # Shoulders
        (5, 7), (7, 9),  # Left arm
        (6, 8), (8, 10),  # Right arm
        (5, 11), (6, 12),  # Torso
        (11, 12),  # Hips
        (11, 13), (13, 15),  # Left leg
        (12, 14), (14, 16),  # Right leg
    ]

    def __init__(self, input_size=(256, 256), num_keypoints=17):
        self.input_size = input_size
        self.num_keypoints = num_keypoints

        # Simulated heatmap model weights
        self.heatmap_weights = np.random.randn(
            num_keypoints, 64, input_size[0]//4, input_size[1]//4
        ) * 0.01

    def generate_heatmaps(self, person_region):
        """Generate keypoint heatmaps for a detected person."""
        h, w = person_region.shape[:2]
        heatmap_h, heatmap_w = h // 4, w // 4

        heatmaps = np.zeros((self.num_keypoints, heatmap_h, heatmap_w))

        # Simulate keypoint positions (top-down view adjustments)
        keypoint_positions = [
            (heatmap_h//2, heatmap_w//2),      # Nose (center of head)
            (heatmap_h//2-2, heatmap_w//2-2),   # Left eye
            (heatmap_h//2-2, heatmap_w//2+2),   # Right eye
            (heatmap_h//2-1, heatmap_w//2-4),   # Left ear
            (heatmap_h//2-1, heatmap_w//2+4),   # Right ear
            (heatmap_h//3, heatmap_w//3),        # Left shoulder
            (heatmap_h//3, 2*heatmap_w//3),     # Right shoulder
            (heatmap_h//2, heatmap_w//4),        # Left elbow
            (heatmap_h//2, 3*heatmap_w//4),     # Right elbow
            (2*heatmap_h//3, heatmap_w//5),     # Left wrist
            (2*heatmap_h//3, 4*heatmap_w//5),   # Right wrist
            (2*heatmap_h//3, heatmap_w//3),     # Left hip
            (2*heatmap_h//3, 2*heatmap_w//3),   # Right hip
            (5*heatmap_h//6, heatmap_w//4),     # Left knee
            (5*heatmap_h//6, 3*heatmap_w//4),   # Right knee
            (heatmap_h-1, heatmap_w//5),        # Left ankle
            (heatmap_h-1, 4*heatmap_w//5),      # Right ankle
        ]

        for kp_id, (ky, kx) in enumerate(keypoint_positions):
            if ky < heatmap_h and kx < heatmap_w:
                # Generate Gaussian heatmap
                y, x = np.ogrid[:heatmap_h, :heatmap_w]
                sigma = 2
                heatmap = np.exp(-((x - kx)**2 + (y - ky)**2) / (2 * sigma**2))
                heatmaps[kp_id] = heatmap

        return heatmaps

    def decode_heatmaps(self, heatmaps, threshold=0.3):
        """Decode heatmaps to keypoint coordinates."""
        keypoints = []

        for kp_id in range(self.num_keypoints):
            heatmap = heatmaps[kp_id]

            # Find maximum response
            max_idx = np.unravel_index(np.argmax(heatmap), heatmap.shape)
            max_val = heatmap[max_idx]

            if max_val > threshold:
                keypoints.append(Keypoint(
                    x=float(max_idx[1]),
                    y=float(max_idx[0]),
                    confidence=float(max_val),
                    keypoint_id=kp_id
                ))
            else:
                keypoints.append(Keypoint(
                    x=0.0, y=0.0,
                    confidence=0.0,
                    keypoint_id=kp_id
                ))

        return keypoints

    def adjust_for_aerial_view(self, keypoints, altitude=50):
        """Adjust keypoints for top-down aerial perspective."""
        # Aerial view transformations
        scale_factor = 100 / altitude  # Higher altitude = smaller scale

        adjusted = []
        for kp in keypoints:
            # Scale coordinates
            new_x = kp.x * scale_factor
            new_y = kp.y * scale_factor

            # Adjust for top-down view (foreshortening)
            # Vertical body parts appear compressed
            if kp.keypoint_id in [13, 14, 15, 16]:  # Knees and ankles
                new_y = kp.y * 0.6  # Compress leg appearance

            adjusted.append(Keypoint(
                x=new_x,
                y=new_y,
                confidence=kp.confidence,
                keypoint_id=kp.keypoint_id
            ))

        return adjusted

    def estimate_pose(self, person_image, altitude=50):
        """Complete pose estimation pipeline."""
        # Generate heatmaps
        heatmaps = self.generate_heatmaps(person_image)

        # Decode to keypoints
        keypoints = self.decode_heatmaps(heatmaps)

        # Adjust for aerial view
        keypoints = self.adjust_for_aerial_view(keypoints, altitude)

        return keypoints

    def compute_skeleton(self, keypoints, image_shape):
        """Compute skeleton lines from keypoints."""
        skeleton = []
        h, w = image_shape[:2]

        for start_idx, end_idx in self.SKELETON:
            kp_start = keypoints[start_idx]
            kp_end = keypoints[end_idx]

            if kp_start.confidence > 0.3 and kp_end.confidence > 0.3:
                skeleton.append({
                    'start': (int(kp_start.x), int(kp_start.y)),
                    'end': (int(kp_end.x), int(kp_end.y)),
                    'confidence': (kp_start.confidence + kp_end.confidence) / 2
                })

        return skeleton

# Example: Aerial pose estimation
np.random.seed(42)
estimator = AerialPoseEstimator()

print("Aerial Pose Estimation")
print("=" * 50)

# Simulate person region from drone
person_region = np.random.randint(0, 255, (64, 64, 3), dtype=np.uint8)

# Estimate pose
keypoints = estimator.estimate_pose(person_region, altitude=30)

print("Detected Keypoints (top-down adjusted):")
kp_names = ['Nose', 'L-Eye', 'R-Eye', 'L-Ear', 'R-Ear',
            'L-Shoulder', 'R-Shoulder', 'L-Elbow', 'R-Elbow',
            'L-Wrist', 'R-Wrist', 'L-Hip', 'R-Hip',
            'L-Knee', 'R-Knee', 'L-Ankle', 'R-Ankle']

for i, (kp, name) in enumerate(zip(keypoints, kp_names)):
    if kp.confidence > 0.3:
        print(f"  {name}: ({kp.x:.1f}, {kp.y:.1f}) conf={kp.confidence:.2f}")

# Compute skeleton
skeleton = estimator.compute_skeleton(keypoints, (64, 64))
print(f"\nSkeleton segments: {len(skeleton)}")

Pose-Based Action Recognition

python
from collections import deque

class ActionRecognizer:
    """Recognize actions from pose sequences."""

    ACTIONS = {
        'walking': 'Person is walking',
        'running': 'Person is running',
        'standing': 'Person is standing still',
        'sitting': 'Person is sitting',
        'fallen': 'Person appears to have fallen',
        'waving': 'Person is waving hand',
        'carrying': 'Person is carrying object',
    }

    def __init__(self, sequence_length=10):
        self.sequence_length = sequence_length
        self.pose_history = deque(maxlen=sequence_length)

    def update(self, keypoints):
        """Update with new pose and predict action."""
        self.pose_history.append(keypoints)

        if len(self.pose_history) < 3:
            return 'unknown', 0.0

        # Compute motion features
        features = self._extract_motion_features()

        # Simple rule-based classification
        action, confidence = self._classify_action(features)

        return action, confidence

    def _extract_motion_features(self):
        """Extract motion features from pose sequence."""
        poses = list(self.pose_history)

        features = {}

        # Average keypoint velocity
        velocities = []
        for i in range(1, len(poses)):
            vel = []
            for kp1, kp2 in zip(poses[i-1], poses[i]):
                dx = kp2.x - kp1.x
                dy = kp2.y - kp1.y
                vel.append(np.sqrt(dx**2 + dy**2))
            velocities.append(np.mean(vel))

        features['avg_velocity'] = np.mean(velocities)
        features['velocity_variance'] = np.var(velocities)

        # Joint angle changes
        if len(poses) >= 2:
            # Elbow angle
            angles = []
            for pose in poses:
                if (pose[7].confidence > 0.3 and pose[9].confidence > 0.3):
                    angle = self._compute_angle(
                        pose[5], pose[7], pose[9]  # Shoulder, elbow, wrist
                    )
                    angles.append(angle)

            if angles:
                features['elbow_angle_mean'] = np.mean(angles)
                features['elbow_angle_std'] = np.std(angles)
            else:
                features['elbow_angle_mean'] = 0
                features['elbow_angle_std'] = 0
        else:
            features['elbow_angle_mean'] = 0
            features['elbow_angle_std'] = 0

        # Body center height (for sitting/standing detection)
        center_heights = []
        for pose in poses:
            if pose[11].confidence > 0.3 and pose[12].confidence > 0.3:  # Hips
                center_y = (pose[11].y + pose[12].y) / 2
                center_heights.append(center_y)

        if center_heights:
            features['avg_hip_height'] = np.mean(center_heights)
            features['hip_height_variance'] = np.var(center_heights)
        else:
            features['avg_hip_height'] = 0
            features['hip_height_variance'] = 0

        return features

    def _compute_angle(self, p1, p2, p3):
        """Compute angle between three points."""
        v1 = np.array([p1.x - p2.x, p1.y - p2.y])
        v2 = np.array([p3.x - p2.x, p3.y - p2.y])

        cos_angle = np.dot(v1, v2) / (np.linalg.norm(v1) * np.linalg.norm(v2) + 1e-6)
        angle = np.arccos(np.clip(cos_angle, -1, 1))
        return np.degrees(angle)

    def _classify_action(self, features):
        """Classify action based on motion features."""
        action = 'unknown'
        confidence = 0.0

        # Running: high velocity, high variance
        if features['avg_velocity'] > 5 and features['velocity_variance'] > 2:
            action = 'running'
            confidence = min(0.95, 0.6 + features['avg_velocity'] * 0.05)

        # Walking: moderate velocity
        elif features['avg_velocity'] > 2:
            action = 'walking'
            confidence = min(0.9, 0.5 + features['avg_velocity'] * 0.1)

        # Standing: low velocity, low variance
        elif features['avg_velocity'] < 1 and features['velocity_variance'] < 0.5:
            action = 'standing'
            confidence = 0.85

        # Sitting: low velocity, specific hip height
        elif features['avg_velocity'] < 1 and features['avg_hip_height'] > 30:
            action = 'sitting'
            confidence = 0.75

        # Fallen: very low, specific pose
        elif features['avg_hip_height'] > 40 and features['avg_velocity'] < 0.5:
            action = 'fallen'
            confidence = 0.8

        # Waving: high elbow angle variance
        elif features['elbow_angle_std'] > 20:
            action = 'waving'
            confidence = 0.7

        return action, confidence

# Example: Action recognition from pose sequence
np.random.seed(42)
recognizer = ActionRecognizer(sequence_length=10)

print("Action Recognition from Pose Sequences")
print("=" * 50)

# Simulate walking sequence
for frame in range(15):
    # Create keypoints with walking motion
    keypoints = []
    base_y = 30 + frame * 2

    for kp_id in range(17):
        x = 32 + np.sin(frame * 0.5 + kp_id * 0.3) * 5
        y = base_y + np.cos(frame * 0.5 + kp_id * 0.2) * 3
        conf = 0.7 + np.random.uniform(-0.1, 0.1)

        keypoints.append(Keypoint(x=x, y=y, confidence=conf, keypoint_id=kp_id))

    action, confidence = recognizer.update(keypoints)

    if frame >= 3 and (frame + 1) % 3 == 0:
        print(f"Frame {frame+1}: {action} ({confidence:.1%})")

print("\nAction recognition complete!")

Hands-On Project: Search and Rescue Pose Detector

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Build a pose detection system for search and rescue operations.

python
from dataclasses import dataclass
from typing import List

@dataclass
class RescueAlert:
    """Alert for potential rescue situations."""
    person_id: int
    location: tuple
    alert_type: str
    severity: str
    confidence: float

class SearchRescuePoseDetector:
    """Pose-based detection system for search and rescue."""

    def __init__(self, grid_size=100):
        self.grid_size = grid_size
        self.person_poses = {}
        self.alerts = []

        # Emergency pose indicators
        self.emergency_indicators = {
            'lying_down': self._check_lying_down,
            'waving_distress': self._check_distress_waving,
            'immobile': self._check_immobile,
            'isolated': self._check_isolated,
        }

    def _check_lying_down(self, keypoints):
        """Check if person appears to be lying down."""
        if len(keypoints) < 17:
            return False

        # Check if head and feet are at similar height (top-down view)
        head_y = np.mean([kp.y for kp in keypoints[:5] if kp.confidence > 0.3])
        feet_y = np.mean([kp.y for kp in keypoints[15:17] if kp.confidence > 0.3])

        if head_y > 0 and feet_y > 0:
            # In top-down view, lying down means spread out
            spread = abs(head_y - feet_y)
            return spread < 15  # Small vertical spread = lying down

        return False

    def _check_distress_waving(self, keypoints):
        """Check for distress waving pattern."""
        if len(keypoints) < 11:
            return False

        # Check wrist positions relative to shoulders
        l_wrist = keypoints[9]
        r_wrist = keypoints[10]
        l_shoulder = keypoints[5]
        r_shoulder = keypoints[6]

        if all(kp.confidence > 0.3 for kp in [l_wrist, r_wrist, l_shoulder, r_shoulder]):
            # Hands raised above shoulders
            hands_above = (l_wrist.y < l_shoulder.y or r_wrist.y < r_shoulder.y)
            return hands_above

        return False

    def _check_immobile(self, person_id, current_poses):
        """Check if person has been immobile for extended period."""
        if person_id not in self.person_poses:
            return False

        history = self.person_poses[person_id]
        if len(history) < 5:
            return False

        # Check position variance over recent frames
        recent = history[-5:]
        positions = [(p['position'][0], p['position'][1]) for p in recent]
        variance = np.var(positions, axis=0)

        return np.sum(variance) < 5  # Very little movement

    def _check_isolated(self, person_id, all_persons):
        """Check if person is isolated from others."""
        if person_id not in self.person_poses:
            return False

        my_pos = np.array(self.person_poses[person_id][-1]['position'])

        for other_id, other_data in self.person_poses.items():
            if other_id != person_id and other_data:
                other_pos = np.array(other_data[-1]['position'])
                distance = np.linalg.norm(my_pos - other_pos)
                if distance < 200:  # Within 200 pixels
                    return False

        return True

    def process_frame(self, frame_id, detected_poses):
        """Process frame with detected poses."""
        frame_alerts = []

        for person_id, pose_data in detected_poses.items():
            keypoints = pose_data['keypoints']
            position = pose_data['position']

            # Update history
            if person_id not in self.person_poses:
                self.person_poses[person_id] = []

            self.person_poses[person_id].append({
                'frame': frame_id,
                'position': position,
                'keypoints': keypoints
            })

            # Check emergency indicators
            for indicator_name, check_func in self.emergency_indicators.items():
                if indicator_name == 'immobile':
                    is_emergency = check_func(person_id, self.person_poses)
                elif indicator_name == 'isolated':
                    is_emergency = check_func(person_id, self.person_poses)
                else:
                    is_emergency = check_func(keypoints)

                if is_emergency:
                    alert = RescueAlert(
                        person_id=person_id,
                        location=position,
                        alert_type=indicator_name,
                        severity='high' if indicator_name in ['lying_down', 'immobile'] else 'medium',
                        confidence=0.8
                    )
                    frame_alerts.append(alert)
                    self.alerts.append(alert)

        return frame_alerts

    def generate_report(self):
        """Generate search and rescue report."""
        report = {
            'total_persons_tracked': len(self.person_poses),
            'total_alerts': len(self.alerts),
            'alerts_by_type': {},
            'alerts_by_severity': {'high': 0, 'medium': 0},
            'persons_of_concern': []
        }

        for alert in self.alerts:
            report['alerts_by_type'][alert.alert_type] = \
                report['alerts_by_type'].get(alert.alert_type, 0) + 1
            report['alerts_by_severity'][alert.severity] += 1

        # Find persons with multiple alerts
        person_alerts = {}
        for alert in self.alerts:
            if alert.person_id not in person_alerts:
                person_alerts[alert.person_id] = []
            person_alerts[alert.person_id].append(alert)

        for person_id, alerts in person_alerts.items():
            if len(alerts) >= 2:
                report['persons_of_concern'].append({
                    'person_id': person_id,
                    'alert_count': len(alerts),
                    'alert_types': list(set(a.alert_type for a in alerts))
                })

        return report

# Example: Search and rescue simulation
np.random.seed(42)
sar_system = SearchRescuePoseDetector()

print("Search and Rescue Pose Detection System")
print("=" * 55)

# Simulate detection frames
for frame in range(20):
    detected_poses = {}

    # Simulate 3 persons
    for person_id in range(3):
        # Create keypoints
        keypoints = []
        base_x = 100 + person_id * 200
        base_y = 150 + (frame if person_id != 2 else 0)  # Person 2 stays still

        for kp_id in range(17):
            x = base_x + np.random.uniform(-5, 5)
            y = base_y + np.random.uniform(-5, 5)
            conf = 0.7 + np.random.uniform(-0.1, 0.1)

            # Person 2: lying down pose
            if person_id == 2 and kp_id > 12:
                y += 20  # Spread out

            keypoints.append(Keypoint(x=x, y=y, confidence=conf, keypoint_id=kp_id))

        detected_poses[person_id] = {
            'keypoints': keypoints,
            'position': (base_x, base_y)
        }

    # Process frame
    alerts = sar_system.process_frame(frame, detected_poses)

    if alerts:
        print(f"\nFrame {frame+1} - ALERTS:")
        for alert in alerts:
            print(f"  Person {alert.person_id}: {alert.alert_type} "
                  f"(severity: {alert.severity})")

# Generate report
report = sar_system.generate_report()
print(f"\nSearch and Rescue Report:")
print(f"  Persons tracked: {report['total_persons_tracked']}")
print(f"  Total alerts: {report['total_alerts']}")
print(f"  Alerts by type: {report['alerts_by_type']}")
print(f"  Persons of concern: {len(report['persons_of_concern'])}")

if report['persons_of_concern']:
    print("\nPersons requiring attention:")
    for person in report['persons_of_concern']:
        print(f"  Person {person['person_id']}: "
              f"{person['alert_count']} alerts "
              f"({', '.join(person['alert_types'])})")

print("\nSearch and rescue system operational!")

Key Takeaways

  1. Aerial pose estimation requires adapting models for top-down views
  2. Keypoint heatmaps predict body joint locations with confidence
  3. Skeleton assembly connects keypoints into meaningful body structures
  4. Action recognition uses temporal pose sequences for behavior analysis
  5. Rescue detection identifies emergency situations from pose patterns

Next, we'll explore gesture recognition for drone-human interaction.

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