1. Quality of Images

2. Geometric Quality of Aerial Images
All aerial images contain geometric distortion
Orthographic – plots position of objects after being projected onto a common plane
Equivalent to looking vertically downward onto a scene from an infinite height

3. Most aerial photos do not provide an orthographic view…they provide a perspective view, which is a geometrically distorted image of the Earth’s surface.

5. Aerial Image Distortion
Six primary sources
Source
Amount of Error
Terrain
Major
Camera Tilt
Film Deformation
Minor
Camera Lens
Atmospheric Bending
Other Camera Errors

6. Terrain Distortion
Terrain variation is often largest source of geometric distortion
Causes relief displacement

7. Displaced location of building corner X True location building corner
Example
Location of tall objects are displaced away from the center of the photograph
Center of photograph X
Displaced location of building corner
X True location building corner

9. Terrain Distortions Terrain distortions are radial
Relief distortions affect angles and distances on an aerial image
Scale is not constant on aerial images
A vertical aerial image taken over varied terrain is not orthographic

10. Camera Tilt Distortion
Camera tilt is when the optical axis points in a non-vertical angle
Results in complex perspective convergence

12. Camera Tilt Distortion
Camera mounting systems are devised to keep optical axis pointing directly below
Tilt is characterized by three angles of rotation
Pitch
Roll
Yaw

14. Other Errors
Radial Lens Displacement – imperfections in camera lens surface
Systematic errors
Ex. Deformed plattern - geometric distortion
Atmospheric Distortion – bending of light

15. Geometric Correction
Photogrammetry provides tools needed to remove geometric distortion from photos
Correction process requires measurement of image coordinates and their corresponding ground coordinates
End result: orthographic image -an image with terrain and perspective distortions removed