Image stitching for mapping in Drone Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of image overlap calculation

What is the output of this code that calculates the overlap percentage between two drone images given their GPS coordinates and image width in meters?

Drone Programming

def calculate_overlap(coord1, coord2, image_width):
    distance = abs(coord2 - coord1)
    overlap = max(0, (image_width - distance) / image_width) * 100
    return round(overlap, 2)

print(calculate_overlap(100.0, 105.0, 10.0))

A 100.0

B 25.0

C 0.0

D 50.0

💡 Hint

Think about how much the images overlap if the distance between centers is less than the image width.

The distance between coordinates is 5 meters. The image width is 10 meters, so overlap is (10 - 5)/10 = 0.5 or 50%.

🧠 Conceptual

intermediate

Key step in image stitching

Which step is essential for stitching multiple drone images into a single map?

A Aligning images based on common features

B Increasing drone flight altitude

C Reducing image resolution

D Changing camera shutter speed

💡 Hint

Think about how images fit together like puzzle pieces.

Aligning images by matching common features ensures they overlap correctly to form a seamless map.

🔧 Debug

advanced

Identify the error in image stitching code

What error does this code raise when trying to stitch images using OpenCV's stitcher?

Drone Programming

import cv2
images = [cv2.imread('img1.jpg'), cv2.imread('img2.jpg')]
stitcher = cv2.Stitcher_create()
status, pano = stitcher.stitch(images)
print(status)

A AttributeError: module 'cv2' has no attribute 'Stitcher_create'

B TypeError: stitch() missing 1 required positional argument

C FileNotFoundError: img1.jpg not found

D No error, prints 0

💡 Hint

Check if the OpenCV version supports the Stitcher_create method.

In some OpenCV versions, Stitcher_create is not available or named differently, causing AttributeError.

📝 Syntax

advanced

Correct syntax for blending images

Which option correctly blends two images img1 and img2 with equal weights using OpenCV?

Drone Programming

import cv2
blended = ???
print(type(blended))

A cv2.add(img1 * 0.5, img2 * 0.5)

B cv2.addWeighted(img1, 0.5, img2, 0.5, 0)

C cv2.blend(img1, img2, 0.5)

D cv2.mixImages(img1, img2, 0.5)

💡 Hint

Look for the OpenCV function that mixes images with weights.

cv2.addWeighted blends two images with specified weights and a scalar added value.

🚀 Application

expert

Number of images needed for full map coverage

A drone camera covers 20 meters width per image. To map a 100m by 100m field with 30% overlap between images, how many images are needed along one side?

A 8

B 6

C 7

D 5

💡 Hint

Calculate effective coverage per image after overlap, then divide field length by that.

Effective coverage per image = 20m * (1 - 0.3) = 14m. Number of images = ceil(100 / 14) = 7.14 → 8 images.

Practice

1. What is the main purpose of image stitching in drone programming?

easy

A. To combine multiple drone photos into one large map

B. To control the drone's flight path

C. To improve the drone's battery life

D. To send live video feed to the operator

Solution

1. Step 1: Understand image stitching concept

   Image stitching is about joining many photos to create a bigger picture.

2. Step 2: Identify the main use in drone programming

   It helps create large maps from many drone images for better area coverage.

3. Final Answer:

   To combine multiple drone photos into one large map -> Option A

4. Quick Check:

   Image stitching = combine photos [OK]

Hint: Image stitching means joining photos into one big map [OK]

Common Mistakes:

• Confusing image stitching with drone control
• Thinking it improves battery life
• Mixing it with live video streaming

2. Which of the following is the correct way to start stitching images side by side in a drone program?

easy

A. stitch(images, method='side_by_side')

B. stitch(images, method='fly_path')

C. stitch(images, method='battery_save')

D. stitch(images, method='live_feed')

Solution

1. Step 1: Identify stitching method names

   Side by side stitching joins images horizontally or vertically.

2. Step 2: Match method to stitching task

   Only 'side_by_side' matches the stitching method; others relate to flight or battery.

3. Final Answer:

   stitch(images, method='side_by_side') -> Option A

4. Quick Check:

   Method 'side_by_side' = stitching images side by side [OK]

Hint: Use method='side_by_side' to join images simply [OK]

Common Mistakes:

• Using unrelated methods like 'fly_path' or 'battery_save'
• Confusing stitching method with drone flight commands
• Misspelling method names

3. Given the code snippet:

images = ['img1.jpg', 'img2.jpg', 'img3.jpg']
stitched_map = stitch(images, method='overlap')
print(len(stitched_map))

What will be the output if stitched_map is a combined image with 3 parts?

medium

A. 1

B. 3

C. 0

D. Error

Solution

1. Step 1: Understand the stitch function output

   Stitching combines images into one big image, so the result is a single image object.

2. Step 2: Check what len() returns on the stitched image

   Most image objects do not support len(), so calling len() will cause an error.

3. Final Answer:

   Error -> Option D

4. Quick Check:

   len() on image object causes error [OK]

Hint: len() on stitched image causes error [OK]

Common Mistakes:

• Assuming length equals number of input images
• Expecting len() to work on image object
• Confusing list length with image object length

4. The following code is meant to stitch images with overlap detection but throws an error:

images = ['a.jpg', 'b.jpg']
stitched = stitch(images, method='overlap')
stitched.show()

What is the likely cause of the error?

medium

A. The method 'overlap' is not supported

B. The show() method does not exist for stitched images

C. The stitch function requires images to be loaded, not file names

D. The images list is empty

Solution

1. Step 1: Check input type for stitch function

   Stitch usually needs image data, not just file names as strings.

2. Step 2: Identify error cause

   Passing file names without loading images causes errors when stitching or showing.

3. Final Answer:

   The stitch function requires images to be loaded, not file names -> Option C

4. Quick Check:

   Input must be loaded images, not file names [OK]

Hint: Load images before stitching, not just file names [OK]

Common Mistakes:

• Assuming method 'overlap' is invalid
• Thinking show() method is missing
• Ignoring that images list is not empty

5. You want to create a stitched map from drone images but only include images that have at least 30% overlap with the previous one. Which approach best applies this condition in your stitching code?

hard

A. Stitch all images first, then crop the map to overlapping areas

B. Filter images by overlap percentage before stitching using a function

C. Use method='side_by_side' to ignore overlap

D. Manually stitch images without any overlap checks

Solution

1. Step 1: Understand the overlap condition

   Only images with at least 30% overlap should be included in stitching.

2. Step 2: Choose the best way to apply this condition

   Filtering images before stitching ensures only suitable images are combined.

3. Final Answer:

   Filter images by overlap percentage before stitching using a function -> Option B

4. Quick Check:

   Filter first, then stitch = correct approach [OK]

Hint: Filter images by overlap before stitching [OK]

Common Mistakes:

• Stitching all images then cropping
• Ignoring overlap and stitching side by side
• Manual stitching without overlap checks