Remote Sensing Geometry of Aerial Photographs

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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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Presentation Transcript
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

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 Photograph
• Photogrammetry  - science of making accurate measurements from aerial photographs
2. Basic Elements
• Fiducial marks
• Principle point
• Isocenter

Frame Number

Date of Photography

Mission ID

Principal Point

Fiducial Marks

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

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
3. Relief Displacement
• It increases with (1) increasing height of the feature and (2) the distance from nadir
4. Multiple Photographs
• Forward overlap: 50-60% along flight line; sidelap: 5-15%
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
• Stereoscopic parallax  - difference in appearances of objects due to change in perspectives  - it can be measured to compute the elevations of terrain
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