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A short class with Sarah and her students. The other ways are under More.
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Today, we're going to figure out how many photographs we need to cover a certain area in aerial photogrammetry. Can anyone tell me what parameters we need to consider?
Do we need the area dimensions and the overlap percentages?
Exactly! We'll use the area lengths, overlaps, and the scale of the photography. For example, if we have a longitudinal overlap of 60% and a side overlap of 30%, these will affect our calculations significantly.
How do we use those overlaps to calculate the number of photos?
Great question! We can use the formula: N1 = L / {(1 - OL) scale * photograph dimension} + 1 for longitudinal overlap. Do you want to try calculating for given dimensions?
Sure! If the flight line is 20 km and the photograph size is 23 cm, how would we do that?
Let's work through it step by step together. Remember to convert all units to meters for accuracy.
By the end of this, we’ll know how to determine the total number of photographs altogether, right?
That’s the goal! Let's also summarize our key points: overlapping percentages significantly influence the calculations and proper unit conversion is essential.
Next, let's discuss relief displacement. Who can explain what it is?
Isn't it the effect of elevation difference on how images are captured from the air?
That's correct! The higher an object is, the more it can appear to be displaced from where it actually is in the photo. For a given image displacement, we can calculate its height above datum using the formula d = rh/H.
How does the camera's focal length play a role in this?
Excellent query! It directly affects the scale and the distance estimates. If you understand this, you’re well on your way to mastering photogrammetry!
So, if the focal length increases, does the relief displacement also get affected?
Precisely! Increased focal lengths can lead to more pronounced relief displacements for the same height. Let’s summarize: remember that the displacement depends on elevation, focal length, and the relationship between these factors.
Now, let’s solve some practical example problems to solidify what we’ve learned. Who remembers how to compute the height of the tower using relief displacement?
We use the tower's actual height and the distance from the principal point, along with the formula.
Right again! Can someone give me an example from our notes?
For example, if a tower is 50 m and we measure a displacement of 0.254 cm from its bottom to top image?
Fantastic! Let's apply it in the equation to find heights. Remember to convert and simplify where necessary.
This really helps to understand how the different heights and measurements influence our calculations!
Exactly! Keep practicing these examples to make the concepts second nature!
These are essential for determining how many photographs are needed for complete coverage.
An important phenomenon affecting the perception of heights in aerial images.
Critical for understanding the relationship between photograph distance and actual ground distance.
When towers are tall and shadows are long, the displacement can make the image feel wrong.
Imagine you're a bird flying over a city. As you soar higher, the buildings look smaller; they seem to slide down the photo—this is the relief displacement at work!
For remembering the formula of relief displacement, think 'r h / H' (Remember height over Height).
OL = Overlap Length; remember that for aerial photography maths.
Term
What is relief displacement?
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Term
Explain longitudinal overlap.
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Term
What does scale mean in photography?
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The percentage overlap of one photograph with the previous photograph along the flight line.
The percentage overlap of one photograph with the adjacent photograph across the width.
The apparent displacement of an object in a photograph due to its height above the datum.
The ratio of a distance on the photograph to the corresponding distance on the ground.
The central point of a photograph from which other measurements are derived.
This section explores practical applications and calculations related to photogrammetry and aerial photography.
The section provides detailed examples illustrating how to calculate critical parameters in aerial photogrammetry, including relief displacement and the number of photographs needed for coverage. Key formulas are introduced along with several relevant scenarios to enhance understanding.
In this section, we delve into the technical aspects of aerial photogrammetry through a series of examples that illustrate the calculations of various photogrammetric parameters. Key points covered include the determination of the number of photographs required per flight line, the analysis of relief displacement, and the calculations regarding vertical photographs taken at specific elevations. Each example incorporates the necessary formulas, provides solutions, and emphasizes the significance of understanding these concepts in practical applications. Students will learn to navigate through different parameters such as scale, distances, and overlaps to ensure effective mapping and analysis.