18 Questions
What is the relationship between flying height and photographic scale?
Higher the flying height, smaller the scale
What is the point on the ground vertically beneath the perspective centre of the camera lens?
Ground Nadir
What is the advantage of orthogonal projection in map-making?
Distances, angles, and areas on the plane are independent of elevation differences
What is the term for the distance from the optical centre of the lens to the focal plane when the camera is focused at infinity?
Focal length
What is the term used for two successive photographs taken during a flight line?
Stereo-pair
What is the characteristic of an orthophoto that makes it an alternate to a map?
It has a constant scale throughout the photograph
What is the point on the photograph where the fiducial axes intersect?
Photograph centre
What is the minimum amount of end lap required between aerial photographs in the same flight line?
60%
What is the scale of a vertical photograph if a section line measures 150.62 mm, and the length of the section line on the map is 10.69 cm, with a map scale of 1/15000?
1/15100
What is the classification of terrain if the scale of the photograph is S = f / (H - h)?
Variable terrain
What is the term used for the overlap between photographs in adjacent parallel flight lines?
Side lap
What is the term used for the common overlap between three successive photographs?
Superlap
What is the primary purpose of fiducial marks in photogrammetry?
To form four sharp marks on the photographs
What is the minimum tilt allowed for a photograph to be considered a vertical photograph?
30 degrees
What is the term used to describe the difference in elevation between two points on a stereoscopic pair of photographs?
Parallax
What is the process of estimating the scale of a vertical photograph over a variable terrain?
Geometry of a vertical photograph calculation
What is the application of photogrammetry in environmental monitoring?
Estimation of legacy waste
What is the term used to describe the process of recording, measuring, and interpreting aerial photographic images and patterns of recorded radiant electromagnetic energy?
Photogrammetry
Study Notes
Aerial Photographs and Photogrammetry
- Aerial photographs are exposed to have an overlap of 60% between successive photographs in a flight line, called "end lap", and between adjacent parallel flight lines, called "side lap".
- This overlap enables generating 3D views of common areas between two successive photographs.
Types of Photographs
- Vertical photograph: exposed with the optical axis of the camera coinciding with the direction of gravity.
- Tilted photograph: taken with the optical axis unintentionally tilted from the vertical by a small amount (less than 30°).
Photo Coordinate System
- Fiducial Marks: index marks rigidly connected with the camera lens, forming four sharp marks on the photographs.
- Flying Height: the height at which the aircraft flies when taking photographs, directly related to the photographic scale.
- Photograph Centre: the point on the photograph at the intersection of the fiducial axes.
Photogrammetry
- Definition: the art, science, and technology of obtaining reliable information about physical objects and the environment through recording, measuring, and interpreting aerial photographic images.
- Applications: estimation of legacy waste, and more.
Scale of a Vertical Aerial Photograph
- Formula for scale of a vertical photograph on flat terrain: 𝑓 𝑆= 𝐻 ′
- Formula for scale of a vertical photograph on variable terrain: 𝑆 𝐴= 𝑓 𝐻 − h
Other Key Concepts
- Superlap: the common overlap between three successive photographs.
- Stereoscope and parallax in stereoscopic views: used to find elevation differences.
- Orthophotos: aerial photographs rectified by combining photogrammetric principles with DEM data, with a uniform scale throughout.
Test your understanding of photogrammetry, a geospatial technique used to extract information from photographs. Learn about the different types of photographs, photo coordinate systems, and how to find elevation differences using stereoscopic parallax. Apply your knowledge of photogrammetry principles and applications.
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