Remote Sensing Geometry of Aerial Photographs

1. Remote SensingGeometryof 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. 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

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. Flight line # 1 Flight line # 2 Stereoscopic Pairs

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