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Remote Sensing Geometry of Aerial Photographs. 1. Geometry of Vertical Aerial Photograph . Oblique photographs - Cameras oriented toward the side of the aircraft

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1 geometry of vertical aerial photograph
1. Geometry of Vertical Aerial Photograph
  • Oblique photographs

- Cameras oriented toward the side of the aircraft

  • Vertical photographs - camera aimed directly at the ground surface from above  - difficult to recognize ground features but measurements can be made
nir aerial photographs

Photo taken as part of the NAPP mission in color IR at a scale of 1:40,000. (1”=3,333’). This image has been enlarged by x factor.

NIR Aerial Photographs
1 geometry of vertical aerial photograph7
1. Geometry of Vertical Aerial Photograph
  • Photogrammetry  - science of making accurate measurements from aerial photographs
2 basic elements
2. Basic Elements
  • Fiducial marks
  • Principle point
  • Ground nadir
  • Photographic nadir
  • Isocenter

Frame Number

Date of Photography

Mission ID

Nadir Point

Principal Point

Fiducial Marks

2 basic elements10
2. Basic elements
  • Fiducial marks - at the edges and corners recorded during exposure
  •  Principle point  - intersection of lines connecting opposite pairs of fiducial marks  
basic elements
Basic Elements
  • Ground nadir  - point on the ground vertically beneath the center of the camera lens during exposure
  •  Photographic nadir  - intersection of the photograph and the vertical line that intersects the ground nadir and the center of the lens
basic elements12
Basic Elements
  • Isocenter    - the focus of tilt    - on a true vertical photo, the isocenter, the principle point, and the photographic nadir coincide
vertical aerial photography14
Vertical Aerial Photography
  • Most common type aerial photography
  • Camera axis as vertical as possible
  • Generally a tilt or error introduced in photography of 1 – 3 degrees
  • Small amount can be easily adjusted
geometric errors of vertical aerial photography
Geometric Errors of Vertical Aerial Photography
  • Optical distortion   - caused by camera problems
  • Tilt - caused by displacement of the focal plane from a truly horizontal position by aircraft motion (attitude)

  - image areas on the upper side of the tilt depict ground features in smaller than the normal scale

  - Roll, Crab, Pitch

  • Roll distortion  - about its flight axis - roll compensation
  • Crab distortion  - caused by deflection of aircraft due to crosswind - corrections: on the plane or by computer
  • Pitch distortion  - result in local scale change  - can be ignored in most analyses
3 relief displacement
3. Relief Displacement
  • The direction of relief displacement is radial from nadir
  • It increases with (1) increasing height of the feature and (2) the distance from nadir
4 multiple photographs
4. Multiple Photographs
  • Forward overlap: 50-60% along flight line; sidelap: 5-15%
pre marked points
Pre-Marked Points
  • Panels (targets) are placed at control point locations prior to the flight so that they will appear on the photography
  • Panels size depends on the scale of the photography
  • Painted on hard surfaces
  • Made of plastic sheeting, cloth, or wood on grass or soil surfaces
multiple photos
Multiple Photos
  • Stereoscopic parallax  - difference in appearances of objects due to change in perspectives  - it can be measured to compute the elevations of terrain
5 orthophotographs
5. Orthophotographs
  • Aerial photographs without geometric errors introduced by tilt or relief displacement
  •  Orthophotomaps and digital orthophoto Quarter Quad (DOQQ) - show correct planimetric position and consistent scale
  • Chapter 3
multiple photos33
Multiple Photos
  • Conjugate principle - the image centers of preceding and succeeding photographs - lines connecting the conjugate principle points define flight axis - parallax occurs parallel to the line of flight