Surveying and mapping with photogrammetry in Drone Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Calculate Ground Sampling Distance (GSD)

What is the output of this code that calculates the Ground Sampling Distance (GSD) in centimeters?

Drone Programming

def calculate_gsd(sensor_width_mm, image_width_px, flight_height_m, focal_length_mm):
    # GSD formula: (sensor_width * flight_height * 100) / (focal_length * image_width)
    return (sensor_width_mm * flight_height_m * 100) / (focal_length_mm * image_width_px)

sensor_width = 36  # mm
image_width = 6000  # pixels
flight_height = 120  # meters
focal_length = 50  # mm

gsd = calculate_gsd(sensor_width, image_width, flight_height, focal_length)
print(round(gsd, 2))

A 14.4

B 1.44

C 0.144

D 144.0

💡 Hint

Remember to convert flight height to centimeters by multiplying by 100.

The formula calculates GSD in centimeters per pixel. Plugging in the values: (36 * 120 * 100) / (50 * 6000) = 1.44 cm/pixel.

🧠 Conceptual

intermediate

Understanding Overlap in Photogrammetry Flights

Which option correctly describes the purpose of frontlap and sidelap in drone photogrammetry flights?

A They ensure images overlap enough to create 3D models and avoid gaps in data.

B They reduce the flight time by minimizing the number of images taken.

C They control the drone's altitude to maintain a constant speed.

D They adjust the camera's focus to improve image sharpness.

💡 Hint

Think about why multiple images need to cover the same ground area.

Frontlap and sidelap create overlapping images so software can match points between photos to build accurate 3D models and maps.

🔧 Debug

advanced

Fix the Flight Path Calculation Bug

What error does this code raise when calculating the number of flight lines needed for a survey?

Drone Programming

def calculate_flight_lines(area_width_m, swath_width_m):
    # Calculate number of flight lines needed
    lines = area_width_m / swath_width_m
    return int(lines)

area_width = 250
swath_width = 60

print(calculate_flight_lines(area_width, swath_width))

A Raises a TypeError

B Raises a ZeroDivisionError

C Returns 5 correctly

D Returns 4, but should be 5 to cover entire area

💡 Hint

Check how integer division truncates decimals.

The code truncates the division result, so 250/60 = 4.16 becomes 4, which is not enough to cover the full width. It should round up to 5.

📝 Syntax

advanced

Identify the Syntax Error in Image Geotagging Code

Which option contains the syntax error in this snippet that assigns GPS coordinates to images?

Drone Programming

images = ['img1.jpg', 'img2.jpg', 'img3.jpg']
gps_coords = [(40.7128, -74.0060), (40.7130, -74.0055), (40.7132, -74.0050)]

for i in range(len(images)):
    print(f"Assigning {gps_coords[i]} to {images[i]}")

A Missing colon after for loop declaration

B Incorrect variable name gps_coords misspelled as gps_coord

C Using parentheses instead of square brackets for list indexing

D Missing quotation marks around image filenames

💡 Hint

Check the syntax of the for loop line.

The for loop line is missing a colon at the end, which causes a SyntaxError.

🚀 Application

expert

Determine the Number of Images for Full Coverage

A drone camera has a sensor width of 24 mm and takes images 4000 pixels wide. The flight height is 100 meters, and the focal length is 35 mm. The survey area is 500 meters wide. The swath width is calculated using the formula: swath_width = (sensor_width * flight_height) / focal_length. If the sidelap is 70%, how many images are needed along the width to cover the area fully?

Choose the correct number of images.

A 20

B 30

C 25

D 35

💡 Hint

Calculate swath width first, then adjust for sidelap, then divide area width by effective swath width and round up.

Swath width = (24 * 100) / 35 ≈ 68.57 m. Effective swath width with 70% sidelap = 68.57 * (1 - 0.7) = 20.57 m. Number of images = 500 / 20.57 ≈ 24.3, rounded up to 25.