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BASIC CONCEPTS OF PHOTOGRAMMETRY

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- 1. NAMITHA M. R. ID. No: 2015664502 M. Tech, LWME TNAU BASIC PRINCIPLES OF PHOTOGRAMMETRY
- 2. Science and technology of obtaining spatial measurements and other geometrically reliable derived products from photographs Photogrammetry
- 3. Analysis procedures ranges form obtaining approximate distances, areas and elevations using hardcopy photographic products, unsophisticated equipment and simple geometric concepts to generating precise Digital Elevation Models (DEMs), orthophotos, thematic GIS data and other derived products through the use of digital raster images and relatively sophisticated analytical techniques Contd…
- 4. Photogrammetric operation involving the use of digital raster photogrammetric image data – Digital / Softcopy photogrammetry Most common use of photogrammetry- To produce hardcopy topographic maps Contd…
- 5. Determining the scale of a vertical photograph and estimating the horizontal ground distances Using area measurements made on a vertical photograph to determine the equivalent areas in a ground coordinate system Quantifying the effect of relief displacement on vertical areal photographs Photogrammetric activities
- 6. Determining object heights from relief displacement measurements Determining object heights and terrain elevations by measuring image parallax Using ground control points Producing maps and orthophotos Preparing a flight plan to acquire aerial photography Contd…
- 7. Geometric types of aerial photographs :- i. Vertical photographs: • Made with the camera axis directed as vertically as possible • Unavoidable tilts cause slight (1° to 3°) unintentional inclination of the camera optical axis- Tilted photographs Basic Geometric Characteristics Of Aerial Photographs
- 8. ii. Oblique photographs: • Aerial photographs taken with intentional inclination of the camera axis • High oblique photographs include an image of the horizon and low oblique photographs do not. Contd…
- 9. Taking vertical aerial photographs :- • Mostly taken with flight cameras along the flight lines or flight strips • Nadir line- Line traced on the ground directly beneath the aircraft during acquisition of photography • Successive photographs are generally taken with some degrees of end lap • An end lap of 50% is essential for total stereoscopic coverage of a project area Contd…
- 10. Contd…
- 11. • Stereoscopic coverage consists of adjacent pairs of overlapping vertical photographs called stereo pairs • Stereo pairs provides 2 different perspectives of the ground area in their region of end lap • When stereo pairs are viewed through a stereoscope, the result is the perception of a 3D stereo model Contd…
- 12. • Intervalometer: Device that automatically trips the camera shutter at desired time intervals. • Stereoscopic overlap area: Area included in the overlap of successive photographs • Air base: Ground distance between the photo centers at the times of exposure Contd…
- 13. • The ratio between the airbase and the flying height above ground determines the vertical exaggeration perceived by photo interpreters • Larger the base-height ratio, greater the vertical exaggeration Contd…
- 14. • Adjacent strips are provided with a side lap of 30% • Multiple strips comprise what is called a block of photographs Contd…
- 15. Contd…
- 16. Geometric elements of a vertical photograph:- Contd…
- 17. • Light rays from terrain object Camera lens exposure station(L) Plane of the film negative • The negative is located behind the lens at a distance equal to the lens focal length, f • Paper print positive image positions can be depicted diagrammatically in front of the lens in a plane located at a distance, f Contd…
- 18. • The x axis coincides with the line of flight and the y axis is located 90° counter clockwise from the positive x axis • Photo coordinate point o is assumed to coincide with the principal point • Principal point - Intersection of lens optical axis and the film plane Contd…
- 19. • Ground principal point, (O)– Point where the prolongation of the optical axis of the camera intersects the terrain • Images for terrain points A, B, C, D and E appear geometrically reversed on the negative at a’, b’, c’, d’ and e’ and in proper geometric relationship on the positive at a, b, c, d and e Contd…
- 20. Photo coordinate measurement:- • Engineer’s scale or metric scale • Coordinate digitizer • Comparator – Mono comparator or Stereo comparator Contd…
- 21. The relationship between the photograph’s row and column coordinate system and the camera’s fiducial axis coordinate system is determined by a mathematical coordinate transformation between the 2 systems Contd…
- 22. An expression that states that one unit of distance on the photograph represents a specific number of units of actual ground distance Expressed as unit equivalents, representative fractions or ratios Photographic Scale
- 23. Larger scale shows ground features at a larger, more detailed size (eg: 1:10000) Smaller scale shows ground features at a smaller, less detailed size (eg: 1:50,000) Same objects are smaller on a smaller scale photographs than on a larger scale photographs Contd…
- 24. Scale S is computed as the ratio of photo distance d to the ground distance D, Photo Scale, S = 𝑷𝒉𝒐𝒕𝒐 𝑫𝒊𝒔𝒕𝒂𝒏𝒄𝒆 𝑮𝒓𝒐𝒖𝒏𝒅 𝑫𝒊𝒔𝒕𝒂𝒏𝒄𝒆 = 𝒅 𝑫 For a vertical photograph taken over a flat terrain, scale is a function of focal length f of the camera and the flying height H’ above the ground, Scale = 𝑪𝒂𝒎𝒆𝒓𝒂 𝑭𝒐𝒄𝒂𝒍 𝑳𝒆𝒏𝒈𝒕𝒉 𝑭𝒍𝒚𝒊𝒏𝒈 𝑯𝒆𝒊𝒈𝒉𝒕 𝒂𝒃𝒐𝒗𝒆 𝑻𝒆𝒓𝒓𝒂𝒊𝒏 = 𝒇 𝑯′ Contd…
- 25. Average scale computed for the entire photograph, Savg = 𝒇 𝑯−𝒉𝒂𝒗𝒈 where, havg Average elevation of the terrain Contd…
- 26. Contd…
- 27. All points on a map are depicted in their true relative horizontal positions, but points on photo taken over varying terrain are displaced from their true map positions Result of photo scale variation- Geometric distortion Map is a scaled Orographic projection of the ground, whereas a vertical photograph yields a Perspective projection Contd…
- 28. Contd…
- 29. On a map Top view of the object are seen in their true relative horizontal positions On a photo Areas of the terrain at the higher elevations appear larger than corresponding areas lying at lower elevations. top of the objects are always displaced from their bases This distortion is called Relief displacement Relief Displacement
- 30. Causes any object standing above the terrain to lean away from the principal point of a photograph radially Contd…
- 31. Relief displacement, d = 𝒓𝒉 𝑯 where, r radial distance on the photograph from the principal point to the displaced image point h height above datum of the object point H flying height above the same datum chosen to reference h Contd…
- 32. Parallax – Apparent change in relative positions of stationary objects caused by a change in viewing positions This phenomenon is observable when one looks at objects through the side window of a moving vehicle Image Parallax
- 33. THANK YOU

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