RDC_Simulation/docs/protocol.md

Communication Protocol (GPS-Denied)

Message formats for GPS-denied drone operation with camera.

Drone Commands

{
    "thrust": 0.5,
    "pitch": 0.1,
    "roll": -0.2,
    "yaw": 0.0
}

Field	Range	Description
thrust	±1.0	Vertical thrust (positive = up)
pitch	±0.5	Forward/backward tilt
roll	±0.5	Left/right tilt
yaw	±0.5	Rotation

---

Drone Telemetry

Published on /drone/telemetry. No GPS position available.

{
    "imu": {
        "orientation": {"roll": 0.0, "pitch": 0.0, "yaw": 0.0},
        "angular_velocity": {"x": 0.0, "y": 0.0, "z": 0.0},
        "linear_acceleration": {"x": 0.0, "y": 0.0, "z": 9.81}
    },
    "altimeter": {
        "altitude": 5.0,
        "vertical_velocity": -0.1
    },
    "velocity": {"x": 0.0, "y": 0.0, "z": -0.1},
    "landing_pad": {
        "relative_x": 0.5,
        "relative_y": -0.2,
        "distance": 4.5,
        "confidence": 0.85
    },
    "camera": {
        "width": 320,
        "height": 240,
        "fov": 60.0,
        "image": "<base64 encoded JPEG>"
    },
    "landed": false,
    "timestamp": 1.234
}

---

Sensor Details

IMU

Always available.

Field	Unit	Description
orientation.roll/pitch/yaw	radians	Euler angles
angular_velocity.x/y/z	rad/s	Rotation rates
linear_acceleration.x/y/z	m/s²	Acceleration

Altimeter

Always available.

Field	Unit	Description
altitude	meters	Height above ground
vertical_velocity	m/s	Vertical speed

Velocity

Estimated from optical flow.

Field	Unit	Description
x	m/s	Forward velocity
y	m/s	Lateral velocity
z	m/s	Vertical velocity

Landing Pad Detection

May be null if pad not visible!

Field	Unit	Description
relative_x	meters	Forward/back offset (body frame)
relative_y	meters	Left/right offset (body frame)
distance	meters	Vertical distance to pad
confidence	0-1	Detection confidence

Camera

Always available.

Field	Description
width	Image width in pixels
height	Image height in pixels
fov	Horizontal field of view in degrees
image	Base64 encoded JPEG (or null)

---

Using the Camera Image

The camera provides a base64-encoded JPEG image of what the drone sees looking down.

Decoding the Image (Python)

import base64
from PIL import Image
import io

def decode_camera_image(telemetry):
    camera = telemetry.get('camera', {})
    image_b64 = camera.get('image')
    
    if image_b64 is None:
        return None
    
    # Decode base64 to bytes
    image_bytes = base64.b64decode(image_b64)
    
    # Load as PIL Image
    image = Image.open(io.BytesIO(image_bytes))
    
    return image

Using with OpenCV

import base64
import cv2
import numpy as np

def decode_camera_image_cv2(telemetry):
    camera = telemetry.get('camera', {})
    image_b64 = camera.get('image')
    
    if image_b64 is None:
        return None
    
    # Decode base64 to bytes
    image_bytes = base64.b64decode(image_b64)
    
    # Convert to numpy array
    nparr = np.frombuffer(image_bytes, np.uint8)
    
    # Decode JPEG
    image = cv2.imdecode(nparr, cv2.IMREAD_COLOR)
    
    return image

Image Properties

• Resolution: 320 x 240 pixels
• Format: JPEG (quality 70)
• FOV: 60 degrees
• Direction: Downward-facing
• Update Rate: ~5 Hz (every 5th telemetry frame)

---

Rover Telemetry

For internal use by RoverController.

{
    "position": {"x": 1.5, "y": 0.8, "z": 0.15},
    "velocity": {"x": 0.3, "y": 0.4, "z": 0.0},
    "pattern": "circular",
    "timestamp": 1.234
}