1. Remote Sensing Geometry of Aerial Photographs

2. 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

3. Geometry of Aerial Photo

4. Black and White Aerial Photographs

5. Color Aerial Photographs

6. 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.

7. 1. Geometry of Vertical Aerial Photograph
Photogrammetry  - science of making accurate measurements from aerial photographs

8. 2. Basic Elements Fiducial marks Principle point Ground nadir
Photographic nadir
Isocenter

9. Frame Number
Date of Photography
Mission ID
Nadir Point
Principal Point
Fiducial Marks

10. 2. Basic elements
Fiducial marks  - at the edges and corners recorded during exposure
 Principle point  - intersection of lines connecting opposite pairs of fiducial marks  

11. 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

12. Basic Elements
Isocenter    - the focus of tilt    - on a true vertical photo, the isocenter, the principle point, and the photographic nadir coincide

13. Vertical Aerial Photography

14. 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

15. 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

16. Tilt 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

17. Tilt

18. 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

19. Relief Displacement

21. 4. Multiple Photographs
Forward overlap: 50-60% along flight line; sidelap: 5-15%

23. Stereoscopic Pairs
Flight line # 2
Flight line # 1

24. 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

25. Multiple Photos
Stereoscopic parallax  - difference in appearances of objects due to change in perspectives  - it can be measured to compute the elevations of terrain

27. Photogrammetry

29. Measurement

30. Orthophotographs

31. 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

32. Readings
Chapter 3

33. 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