Line following with camera in Drone Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of the line detection function?

Given the following function that processes a camera frame to detect a line's position, what will be the returned value when the line is centered?

Drone Programming

def detect_line_position(frame):
    # frame is a 2D list representing pixel brightness
    width = len(frame[0])
    line_pixels = [x for x in range(width) if frame[len(frame)//2][x] > 200]
    if not line_pixels:
        return None
    position = sum(line_pixels) / len(line_pixels)
    center = width / 2
    offset = position - center
    return offset

# Example frame: center line pixels at positions 4,5,6 with brightness 255
frame = [[0]*10 for _ in range(10)]
for x in [4,5,6]:
    frame[5][x] = 255
print(detect_line_position(frame))

A 1.0

B 0.0

C -1.0

D None

💡 Hint

Think about how the average position of the bright pixels compares to the center of the frame.

The bright pixels are at positions 4, 5, and 6. Their average is (4+5+6)/3 = 5. The center is 10/2 = 5. The offset is 5 - 5 = 0.0.

🧠 Conceptual

intermediate

Which sensor data is most useful for line following?

For a drone following a line on the ground using a camera, which type of data is most important to extract from the camera feed?

A The position of the line relative to the drone's center

B The color histogram of the entire frame

C The total brightness of the frame

D The GPS coordinates of the drone

💡 Hint

Think about what helps the drone stay on the line.

The drone needs to know where the line is relative to its center to adjust its path. The position of the line is key.

🔧 Debug

advanced

Why does this line following code cause a crash?

Consider this code snippet for line following. It crashes with an error. What is the cause?

Drone Programming

def follow_line(frame):
    width = len(frame[0])
    line_pos = None
    for x in range(width):
        if frame[len(frame)//2][x] > 200:
            line_pos += x
    return line_pos

A line_pos is None and cannot be added to an integer

B frame is empty causing index error

C The loop variable x is not defined

D The function returns before the loop completes

💡 Hint

Check the initial value of line_pos and how it is used inside the loop.

line_pos starts as None, and adding an integer to None causes a TypeError.

📝 Syntax

advanced

Which option fixes the syntax error in this line detection code?

Fix the syntax error in this dictionary comprehension that maps pixel positions to brightness if brightness is above 200:

{x: frame[5][x] if frame[5][x] > 200 for x in range(10)}

A {x: frame[5][x] if frame[5][x] > 200 for x in range(10)}

B {x: frame[5][x] if frame[5][x] > 200 else 0 for x in range(10)}

C {x: frame[5][x] for x in range(10) if frame[5][x] > 200}

D {x: frame[5][x] for x in range(10) if frame[5][x] < 200}

💡 Hint

Remember the correct order of for and if in comprehensions.

The if filter must come after the for clause in comprehensions.

🚀 Application

expert

How many control adjustments are made in this line following loop?

Consider this drone control loop that adjusts steering based on line position offsets detected from the camera. How many times will the drone adjust its steering if the offsets list is [0.1, -0.2, 0.0, 0.3, -0.1]?

Drone Programming

offsets = [0.1, -0.2, 0.0, 0.3, -0.1]
adjustments = 0
for offset in offsets:
    if abs(offset) > 0.05:
        adjustments += 1
print(adjustments)

A 2

B 3

C 5

D 4

💡 Hint

Count how many offsets have an absolute value greater than 0.05.

Offsets 0.1, -0.2, 0.3, and -0.1 are greater than 0.05 in absolute value, so 4 adjustments.