1 / 41

Aerial Photography and Photogrammetry

Aerial Photography and Photogrammetry. Interpretation and Measurement. 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. Types of aerial photos.

rob
Télécharger la présentation

Aerial Photography and Photogrammetry

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

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 • 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

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

  5. pp

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

  7. 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)

  8. 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.

  9. The Characteristic Curve Image courtesy Sprawls Educational Foundation www.sprawls.org.

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

  11. photo type

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

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

  14. Flight Paths

  15. 5 4 3 2 1 6 7 9 8 10 Flight paths Side overlap Fore and aft overlap

  16. Types of Distortion Caused by Aircraft • Roll • Pitch • Yaw

  17. Distortion caused by roll, pitch and yaw

  18. 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)

  19. Shape

  20. Size

  21. Pattern

  22. Shadow

  23. Color

  24. Texture

  25. Association or Context

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

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

  28. 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)

  29. 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

  30. 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

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

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

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

  34. 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.

More Related