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Aerial Photography and Photogrammetry

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Presentation on theme: "Aerial Photography and Photogrammetry"— Presentation transcript:

1 Aerial Photography and Photogrammetry
Interpretation and Measurement

2 Aerial Photographs Photographs taken from a platform, usually an airplane, flying above the earth’s surface. Can be taken from space (by astronauts) but usually taken from within the atmosphere

3 Types of aerial photos Vertical air photos Oblique air photos
Vertical (on nadir) or nearly vertical angle to the local ground surface (90° ± 3°) Oblique air photos Tilted away from vertical High-oblique Shows the surface, the horizon, and a portion of sky Low-oblique Shows only the surface






9 Information on air photos
Date Mission details Roll + film number Altitude (not always) Fiducial marks

10 pp

11 Analog vs. Digital Analog: Film Digital: Electronic storing device
Emulsions react with light B&W, Color, Color infrared Prints, negatives Digital: Electronic storing device Calibrated sensors Digital values

12 Film vs. Digital Film uses grains of silver chloride embedded in gel rather than pixels. Silver chloride turns to silver (opaque) when exposed to light. Creates a negative. Must pass light through negative to create a positive (print). Typical B&W film sensitive to UV through red wavelengths (panchromatic) Some films sensitive to infrared (IR film)

13 Characteristic Curve Film records radiance as tone – the more light (radiance) that hits the film, the more grains of silver chloride are converted to silver The relationship between radiance and tone is captured in the characteristic curve of the film.

14 The Characteristic Curve
Image courtesy Sprawls Educational Foundation


16 Products Film-based cameras Type Format Media
B&W, color, color infrared, panchromatic Format 9 x 9, 9 x 18, … Media Negative, positive (transparent or opaque) prints

17 photo type

18 Photo Geometry Because airplanes are subject to turbulence, photo geometry can be less predictable than for satellite data

19 Flight characteristics that affect air photo geometry
Flight line orientation (overlap, etc.) Airplane movement caused by turbulence Height, air speed, etc.

20 Flight Paths

21 Flight paths 1 2 3 4 5 6 7 8 9 10 Side overlap Fore and aft overlap

22 Types of Distortion Caused by Aircraft
Roll Pitch Yaw

23 Distortion caused by roll, pitch and yaw

24 Photointerpretation Identifying features on the ground by using information depicted in air photos or satellite data Shape Size Pattern Shadow Tone, color (or gray shade) Texture Context (Association)

25 Shape

26 Size

27 Pattern

28 Shadow

29 Color

30 Texture

31 Association or Context

32 Photointerpretation Keys can be used to standardize interp.
Photointerpretation is both a science and an art

33 Photogrammetry Technique of obtaining reliable measurements of objects from their photographic images Heights of objects Areas Lengths Density Etc.

34 Photographic scale Relationship between the linear distance on a vertical photograph and the corresponding actual distance on the ground Scale is expressed as ‘representative fraction (RF)’ between linear measurements on photo (the numerator) and corresponding distance on the ground (the denominator)

35 Photo scale –> ground distance
Example 1/24,000 or 1:24,000 1 unit on photo = 24,000 units on ground 1 cm = 24,000 cm 1 mm = 24,000 mm 1 inch = 24,000 inches 1 inch = 24,000 in / 12 in/ft = 2,000 ft

36 Scale Scale is the ratio of the measured length of an object on an image to its real length on the ground Always expressed as a ratio (e.g. 1:24,000) Small scale photo covers large area on ground Small scale photo has less detail Large scale photo cover small area on ground Large scale photo has considerable detail


38 Scale: Photo-Ground distance
Scale (RF) when given a photo measurement (PD) and the corresponding ground measurement (GD)

39 Scale: Photo-Ground distance
Distance between two points On the ground = 1200 m In the photo = 5 cm

40 Important facts Scale is not uniform within a photo
Pitch, roll, yaw Terrain Used for vertical airphotos only Average or Nominal scale

41 Photogrammetry Summary
You can calculate many characteristics of ground properties (e.g., building heights, shrub density) from aerial photographs if you know the scale and can use simple geometry and logic.

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