Remote SensingRemote Sensing

GeometryGeometry of Aerial Photographsof Aerial Photographs

1. Geometry of Vertical Aerial 1. Geometry of Vertical Aerial Photograph Photograph

► Oblique photographs Oblique photographs

- Cameras oriented toward the side of the - Cameras oriented toward the side of the aircraftaircraft

► Vertical photographsVertical photographs - camera aimed directly at the ground  - camera aimed directly at the ground surface surface from above from above  - difficult to recognize ground features but  - difficult to recognize ground features but

measurements can be made measurements can be made

Geometry of Aerial PhotoGeometry of Aerial Photo

Black and White Aerial Black and White Aerial PhotographsPhotographs

Color Aerial PhotographsColor Aerial Photographs

NIR Aerial PhotographsNIR 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.

1. Geometry of Vertical Aerial 1. Geometry of Vertical Aerial Photograph Photograph

► Photogrammetry Photogrammetry  - science of making accurate  - science of making accurate measurements from aerial photographs measurements from aerial photographs

2. Basic Elements2. Basic Elements

► Fiducial marksFiducial marks► Principle pointPrinciple point► Ground nadirGround nadir► Photographic nadirPhotographic nadir► Isocenter Isocenter

Date of Photography

Principal Point

Nadir Point

Mission ID

Frame Number

Fiducial Marks

2. Basic elements2. Basic elements

► Fiducial marksFiducial marks - at the edges and corners recorded during  - at the edges and corners recorded during exposure exposure

►   Principle point Principle point  - intersection of lines connecting opposite  - intersection of lines connecting opposite pairs of fiducial marks  pairs of fiducial marks  

Basic ElementsBasic Elements

► Ground nadir Ground nadir  - point on the ground vertically beneath the  - point on the ground vertically beneath the center of the camera lens during exposure center of the camera lens during exposure

►   Photographic nadir Photographic nadir  - intersection of the photograph and the  - intersection of the photograph and the vertical line that intersects the ground nadir vertical line that intersects the ground nadir and the center of the lens and the center of the lens

Basic ElementsBasic Elements

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

Vertical Aerial PhotographyVertical Aerial Photography

Vertical Aerial PhotographyVertical Aerial Photography ► Most common type aerial photographyMost common type aerial photography► Camera axis as vertical as possibleCamera axis as vertical as possible► Generally a tilt or error introduced in Generally a tilt or error introduced in

photography of 1 – 3 degrees photography of 1 – 3 degrees ► Small amount can be easily adjusted Small amount can be easily adjusted

Geometric Errors of Vertical Geometric Errors of Vertical Aerial Photography Aerial Photography

► Optical distortion Optical distortion   - caused by camera problems   - caused by camera problems

► Tilt Tilt - caused by displacement of the focal plane from - caused by displacement of the focal plane from a truly horizontal position by aircraft motion a truly horizontal position by aircraft motion (attitude) (attitude)

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

    - Roll, Crab, Pitch - Roll, Crab, Pitch

TiltTilt► Roll distortion Roll distortion

 - about its flight axis  - about its flight axis - roll compensation - roll compensation

► Crab distortion Crab distortion  - caused by deflection of aircraft due to  - caused by deflection of aircraft due to crosswind crosswind - corrections: on the plane or by computer - corrections: on the plane or by computer

► Pitch distortion Pitch distortion  - result in local scale change  - result in local scale change  - can be ignored in most analyses  - can be ignored in most analyses

TiltTilt

3. Relief Displacement3. Relief Displacement

► The direction of relief displacement is radial The direction of relief displacement is radial from nadir from nadir

► It increases with (1) increasing height of the It increases with (1) increasing height of the feature and (2) the distance from nadir feature and (2) the distance from nadir

Relief DisplacementRelief Displacement

4. Multiple Photographs4. Multiple Photographs

► Forward overlap: 50-60% along flight line; sidelap: Forward overlap: 50-60% along flight line; sidelap: 5-15%5-15%

Stereoscopic PairsStereoscopic Pairs

Flight line # 2

Flight line # 1

Pre-Marked PointsPre-Marked Points

► Panels (targets) are placed at control point Panels (targets) are placed at control point locations prior to the flight so that they will locations prior to the flight so that they will appear on the photographyappear on the photography

► Panels size depends on the scale of the Panels size depends on the scale of the photographyphotography

► Painted on hard surfacesPainted on hard surfaces► Made of plastic sheeting, cloth, or wood on Made of plastic sheeting, cloth, or wood on

grass or soil surfaces grass or soil surfaces

Multiple PhotosMultiple Photos

► Stereoscopic parallax Stereoscopic parallax  - difference in appearances of objects due  - difference in appearances of objects due

to change in perspectives to change in perspectives  - it can be measured to compute the  - it can be measured to compute the elevations of terrainelevations of terrain

PhotogrammetryPhotogrammetry

MeasurementMeasurement

OrthophotographsOrthophotographs

5. Orthophotographs5. Orthophotographs

► AAerial photographs without geometric erial photographs without geometric errors introduced by tilt or relief errors introduced by tilt or relief displacement displacement

►   Orthophotomaps and digital orthophoto Orthophotomaps and digital orthophoto Quarter Quad (Quarter Quad (DOQQ)) - show correct planimetric position and  - show correct planimetric position and consistent scale consistent scale

ReadingsReadings

► Chapter 3Chapter 3

Multiple PhotosMultiple Photos

► Conjugate principle Conjugate principle - the image centers of preceding and - the image centers of preceding and succeeding photographs succeeding photographs - lines connecting the conjugate principle - lines connecting the conjugate principle points define flight axis points define flight axis - parallax occurs parallel to the line of flight - parallax occurs parallel to the line of flight