Industry-relevant training in Business, Technology, and Design to help professionals and graduates upskill for real-world careers.
Fun, engaging games to boost memory, math fluency, typing speed, and English skills—perfect for learners of all ages.
Enroll to start learning
You’ve not yet enrolled in this course. Please enroll for free to listen to audio lessons, classroom podcasts and take practice test.
Listen to a student-teacher conversation explaining the topic in a relatable way.
Let's begin our discussion on determining the scale of a photograph. The formula we generally use is Scale = f / (H - h), where 'f' is the focal length of the camera, 'H' is the height of the aircraft, and 'h' is the height of the terrain.
What happens if the terrain elevation changes while keeping the height of the aircraft constant?
Great question! If the terrain elevation changes, the scale of the photograph will also change. A higher terrain elevation—meaning 'h' increases—reduces the denominator, making the scale smaller or numerically larger. Keep this in mind as it directly impacts the image's accuracy.
Can you give us an example to illustrate this?
Sure! If the aircraft is at 1200 m above mean sea level, and the terrain elevation is 80 m, the scale would be calculated as 15/(1200-80), resulting in around 1:7467, meaning 1 cm on the photo equals 7467 cm on the ground. Remember the acronym 'H change, Scale range!' to help you recall how elevation affects scale.
Does this mean lower elevations give us larger scales – more detail?
Exactly! A smaller 'h' means a larger scale or more detail in your photograph.
To summarize, the scale of a photograph is inversely proportional to the difference in altitude; as the terrain elevation rises relative to your flying height, the scale diminishes.
Next, we will look into determining the flying height needed to achieve a given photograph scale. Can anyone tell me what formula we would use?
Is it the same one for scale? Scale = f / (H - h)?
That's correct! But here, we need to rearrange it to find H. For example, if we want a scale of 1:10,000 with a terrain height of 1600 m, and the focal length is 20 cm, we calculate it as H = scale * focal length + terrain height.
Could you demonstrate that calculation?
Certainly! H = (10,000 * 0.20) + 1600 m gives us 3600 m for the required flying height.
So, is flying higher always better for capturing details?
Not necessarily! While a higher flight allows us to cover larger areas, it reduces detail, making strategic altitudes essential.
In summary, to achieve a specific scale, you can rearrange the formula to solve for H, taking both terrain height and scale into account.
Now let’s explore how we calculate ground distances between points A and B using their coordinates. The equation we'll use is X = x * (H - h) / f and Y = y * (H - h) / f.
Could you show us how we can apply this?
Absolutely! For example, if point A has photographic coordinates of (2.75, 1.39) cm, and B is at (-1.80, 3.72) cm, we first convert the coordinates to ground coordinates using the above formulas.
And then we would find the distance using the formula for calculating lengths, right?
Exactly! After obtaining coordinates for both points, we can use the distance formula to find AB = √[(X_A - X_B)² + (Y_A - Y_B)²].
Interesting! I see how each coordinate contributes to the final measurement.
To summarize, using photographic coordinates in conjunction with altitude and focal length allows us to derive exact ground distances.
Read a summary of the section's main ideas. Choose from Basic, Medium, or Detailed.
In this section, several solved examples provide practical applications of photogrammetric concepts. Key calculations include determining the scale of photographs based on focal length and elevation, flying heights necessary to achieve specified scales, and deriving ground distances from photographic measures. These examples solidify understanding of aerial mapping techniques.
This section encompasses a variety of solved examples that are instrumental in understanding fundamental principles of aerial photogrammetry. The main focus of the examples includes:
These examples, rooted in practical computation, serve as essential exercises to reinforce the knowledge of aerial mapping and triangulation methods introduced earlier in the chapter.
Dive deep into the subject with an immersive audiobook experience.
Signup and Enroll to the course for listening the Audio Book
A vertical photograph was taken at an altitude of 1200 m above msl. Find out the scale of photograph for a terrain lying at an average elevation of (i) 80 m and (ii) 300 m, if the focal length of the camera is 15 cm.
Solution:
H = 1200 m, f = 15 cm, and (i) h = 80 m, (ii) h = 300 m
The scale of a photograph is given by = f / (H - h)
(i) Scale = 15 / (1200 - 80) = 1 / 7467. It means 1 cm on the photo is equal to 7467 cm on the ground.
(ii) Scale = 15 / (1200 - 300) = 1 / 6000.
In this example, we are asked to find the scale of a photograph taken from a height of 1200 meters above mean sea level (msl). The scale formula in photogrammetry relates the focal length of the camera to the difference in altitude between the camera and the terrain.
Thus, the calculation for elevation variations demonstrates how scale changes with differences in height.
Imagine you are trying to measure the distance of a soccer field being viewed from an airplane at a certain altitude. If you're 1200 meters high, the view is vastly different depending on where the soccer field sits. If the field is at sea level (0m), you’ll see it larger than if it’s nestled in a valley (at 300m). Similar to a zoom lens, the further you are from the ground (higher altitude), the less detail you can perceive directly, which is what affects the scale of the images you're capturing.
Signup and Enroll to the course for listening the Audio Book
A camera of 152 mm focal length lens is used to take a vertical photograph from a flying height of 2780 m above mean sea level. If the terrain is flat having an elevation of 500 m above msl, determine the scale of the photograph.
Solution:
f = 152 mm, H = 2780 m, h = 500 m
S = f / (H – h) = (152 / 1000) / (2780 – 500) = 0.152 / 2280 = 1 / 15000.
In this example, we're tasked with determining the scale of a photograph taken from a high altitude over flat terrain.
Think of taking a photograph of a park from a tall radio tower. The higher you go, the more the details blend together, making them appear smaller in the image. A photo taken from a height of 2780 m with minimal elevation change (like a flat terrain park) allows the camera to capture broader areas, but those areas are shown much smaller in the image compared to how they would appear from a lower viewpoint.
Signup and Enroll to the course for listening the Audio Book
A camera of focal length 20 cm is used to take vertical photographs of a terrain having an average elevation of 1600 m above msl. At what height above msl must an aircraft fly to take the photographs at 1:10,000 scale.
Solution:
f = 20 cm, h = 1600 m, and scale = 1:10,000
S = f / (H - h)
H – h = Sf or H = Sf + h
H = (20 / 100) (10,000) + 1600 m = 3600 m.
This example revolves around finding the necessary height for an aircraft to achieve a specific photographic scale.
Imagine you are mapping a city block in detail from the sky. If you want everything to appear clearly and measureable at a scale of 1:10,000, you must establish how high you need to fly. Think of it like a painter needing to determine the right distance to accurately portray all the tiny features of the city on a canvas. The higher the kite flies, the broader the view but lesser the detail retained!
Signup and Enroll to the course for listening the Audio Book
A line AB 300 m long, lying at an elevation of 600 m above msl, measures 9 cm on a vertical photograph. The focal length of the camera lens is 30 cm. Determine the average scale of the photograph if the average elevation of the terrain is 700 m above msl.
Solution:
Ground distance = 300 m, map distance = 9 cm, f = 30 cm, h = 600 m
Map distance / Ground distance = S = f / (H-h)
0.09 / 300 = 0.30 / (H - 600)
H - 600 = (0.30 * 300) / 0.09
H = 1000 + 600 = 1600 m
Now S = f / (H – h)
av av
S = 0.30 / (1600 - 700)
av
= 1 / 3000.
In this scenario, we examine how to establish the scale of a photograph based on specific measurements provided.
Imagine a real estate surveyor trying to find the dimensions of a large lot using an aerial image. By knowing how long a property line is (300 m), they can measure the corresponding line segment on their photograph and use it to figure out the height at which the photograph was taken. This is akin to using a map to gauge a journey's path based on notable landmarks - you compare what's on the map with what exists on the ground!
Signup and Enroll to the course for listening the Audio Book
A line AB measures 12.70 cm on an aerial photograph and the corresponding line measures 2.54 cm on a map at a scale of 1/50,000. The terrain has an average elevation of 200 m above msl. Calculate the flying height of the aircraft, above msl, if the photograph was taken with a camera of 16 cm focal length.
Solution:
Photo distance = 12.70 cm, map distance = 2.54 cm, map scale = 1 / 50,000, h = 200 m, f = 16 cm
Photo distance / map distance = Photo scale / map scale
12.70 / 2.54 = Photo scale / (1 / 50000)
5.0 = 50000 * Photo scale
Photo scale = 1 / 10,000.
Now S = f / (H - h)
1/ 10,000 = 0.16 / (H – 200)
(H - 200) = 0.16 * 10,000
H = 1600 + 200
H = 1800 m.
This example calculates how high an airplane must fly to capture an aerial photograph with specific measurements adjusted for terrain elevation.
When you take a picture of a family picnic from a camper, you want to ensure the whole scene fits the frame. Similarly, in aviation surveying, a pilot must calculate an optimal height to efficiently capture the terrain for mapping accurately. This process is much like a child adjusting their camera's distance to ensure Grandma's apple pie isn't cut off at the side - precise measurements matter!
Learn essential terms and foundational ideas that form the basis of the topic.
Key Concepts
Scale: The ratio of image distance to ground distance, fundamental in photogrammetric calculations.
Flying Height: The height at which an aircraft must fly to achieve the desired scale and detail in aerial photographs.
Ground Distance: The actual distance between geographic points derived from photographic measurements.
Photographic Coordinates: The coordinates used to determine the location of points on a photograph, essential for distance calculations.
See how the concepts apply in real-world scenarios to understand their practical implications.
Example of calculating the scale of a photograph taken at an altitude of 1200 m with terrain elevation at 80 m using a 15 cm focal length.
Calculating the required flying height for a scale of 1:10,000 with a focal length of 20 cm and terrain elevation of 1600 m.
Use mnemonics, acronyms, or visual cues to help remember key information more easily.
To find the scale, just do not fail, divide focal length by height - prevails!
Imagine flying high like a bird, noticing landscapes below as blurred; but with focus tight, your photos delight, revealing the world in exacting sight.
Remember: Fly high, Focus low, Scale grows. H - h over f is the key, let it flow!
Review key concepts with flashcards.
Review the Definitions for terms.
Term: Altitude (H)
Definition:
The height of the aircraft above mean sea level.
Term: Focal Length (f)
Definition:
The distance from the lens to the image sensor in a camera, affecting image scale.
Term: Ground Control Point (GCP)
Definition:
Point with a known location used to help georeference images during mapping.
Term: Minor Control Point (MCP)
Definition:
Points used to establish connections in photogrammetry for better adjustment.
Term: Scale
Definition:
A ratio that expresses the relationship between a distance on a photograph and the corresponding ground distance.