Optical flow for indoor positioning in Drone Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Calculate displacement from optical flow data

Given the optical flow vectors detected by a drone's downward camera, what is the resulting displacement in meters after processing the flow data for 1 second?

Assume the drone's altitude is 2 meters, and the optical flow sensor reports pixel shifts that translate to velocity components as shown in the code.

Drone Programming

altitude = 2.0  # meters
flow_x = 0.1  # meters/second
flow_y = -0.05  # meters/second
time_seconds = 1

displacement_x = flow_x * time_seconds
displacement_y = flow_y * time_seconds

print(f"Displacement X: {displacement_x} m")
print(f"Displacement Y: {displacement_y} m")

A Displacement X: 0.0 m\nDisplacement Y: 0.0 m

B Displacement X: 2.0 m\nDisplacement Y: -1.0 m

C Displacement X: 0.2 m\nDisplacement Y: -0.1 m

D Displacement X: 0.1 m\nDisplacement Y: -0.05 m

💡 Hint

Multiply the velocity components by the time to get displacement.

Displacement is velocity multiplied by time. Here, flow_x and flow_y are velocities in meters per second, so multiplying by 1 second gives the displacement directly.

🧠 Conceptual

intermediate

Understanding optical flow limitations indoors

Which of the following is the main challenge when using optical flow sensors for indoor positioning of drones?

A Strong GPS signals interfering with optical sensors

B Lack of distinct visual features on uniform surfaces

C Excessive sunlight causing sensor overheating

D High altitude causing blurred images

💡 Hint

Think about what optical flow needs to detect movement.

Optical flow relies on detecting changes in visual features. Uniform surfaces indoors often lack distinct features, making it hard to track movement accurately.

🔧 Debug

advanced

Fix the error in optical flow velocity calculation

The following code attempts to calculate the velocity from optical flow pixel shifts and altitude, but it raises an error. Identify the cause and select the correct fixed code.

Drone Programming

pixel_shift_x = 15
pixel_shift_y = 10
altitude = 3.0
focal_length = 2.5
velocity_x = pixel_shift_x * altitude / focal_length
velocity_y = pixel_shift_y * altitude / focal_length

print(f"Velocity X: {velocity_x}")
print(f"Velocity Y: {velocity_y}")

A

velocity_x = pixel_shift_x * altitude / focal_length
velocity_y = pixel_shift_y * altitude / focal_length

B

velocity_x = pixel_shift_x * altitude // focal_length
velocity_y = pixel_shift_y * altitude // focal_length

C

velocity_x = pixel_shift_x / altitude / focal_length
velocity_y = pixel_shift_y / altitude / focal_length

D

velocity_x = pixel_shift_x * altitude * focal_length
velocity_y = pixel_shift_y * altitude * focal_length

💡 Hint

Check the operators used for division and multiplication.

The original code is correct and does not raise an error. Options A, C, and D change the formula incorrectly or use integer division which can cause wrong results.

📝 Syntax

advanced

Identify the syntax error in optical flow data processing

Which option contains a syntax error when trying to create a dictionary of pixel shifts mapped to their velocities?

Drone Programming

pixel_shifts = {'x': 12, 'y': 8}
altitude = 2.5
focal_length = 3.0
velocities = {axis: pixel_shifts[axis] * altitude / focal_length for axis in pixel_shifts}
print(velocities)

A velocities = {axis: pixel_shifts[axis] * altitude / focal_length for axis in pixel_shifts}

B velocities = {axis: pixel_shifts[axis] * altitude / focal_length for axis in pixel_shifts.keys()}

C velocities = {axis: pixel_shifts[axis] * altitude / focal_length for axis pixel_shifts}

D velocities = {axis: pixel_shifts[axis] * altitude / focal_length for axis in pixel_shifts.items()}

💡 Hint

Check the syntax of the for loop in the dictionary comprehension.

Option C is missing the 'in' keyword in the for loop of the dictionary comprehension, causing a syntax error.

🚀 Application

expert

Calculate total distance traveled using optical flow data

A drone collects optical flow velocity data every second for 5 seconds as follows (in meters/second): [0.1, 0.15, 0.12, 0.13, 0.20]. What is the total distance traveled in meters after 5 seconds?

A 0.70

B 0.75

C 0.65

D 0.60

💡 Hint

Sum all velocities and multiply by the time interval (1 second each).

Total distance = sum of velocities * time interval. Sum is 0.1+0.15+0.12+0.13+0.20 = 0.70 meters.