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- 1. GE 178 Lecture 5:Principles of Aerial Photography andPhoto Scale Determination
- 2. Aerial Photo (Image) vs Map• Images central projection, non-uniform scale actual features• Maps orthogonal projection, uniform scale symbols
- 3. Orthogonal vs Perspective Projection
- 4. Orthogonal vs Perspective Projection
- 5. Orthogonal vs Perspective Projection
- 6. Orthogonal vs Perspective Projection
- 7. Vertical Photography
- 8. Vertical Aerial PhotographCharacteristics• tilt ≤ 3° from the vertical• scale is approximately constant throughout the photo• p=i=n• within limitations, a vertical air photo can be used as a map substitute• most common format is a 9 by 9 inch photograph
- 9. Vertical Aerial PhotographNegative plane f (focal length) = C (principal distance) O f=CPositive plane Hmge (flying height) p=i=n Mean ground elevation
- 10. Elements of a Vertical Photograph
- 11. Fiducial Marks• optically projected geometric figures located at either the four corners of a photograph, or on the four sides of a photograph• define the coordinate axes and geometric center of a single aerial photograph• Intersection represents the principal point of the photograph
- 12. Fiducial Marks and Principal Point
- 13. Fiducial Marks
- 14. Three Photo Centers1. Principal Point – geometric center of the photograph; intersection of the line normal to the image plane through the PC2. Nadir – point vertically below the camera at the time the photo was taken; intersection of the plumb line through the PC with the image plane3. Isocenter – point halfway between the principal point and nadir; point intersected by the bisector of the angle between plumb line and optical axis
- 15. Three Photo Centers Ground PPoint Isocenter Nadir
- 16. Kinds of Photography or camera according to focal length (f)• Wide-angle (f = 6 inches)• Normal-angle (f = 12 inches)• Superwide-angle (f = 3.5 inches)
- 17. PhotoScale
- 18. Photoscale of Vertical PhotoRecall: distance on photo f photoscale distance on ground HBut what if not all the required values are given initially, and instead some other parameters are known?
- 19. Determining PhotoscalePhotoscale may also be determined according to:• Smallest detail and resolution• C-factor and desired minimum contour interval• Expected accuracy• Enlargement from photo to map in the instrument
- 20. Smallest detail and resolution• Resolution – smallest distance that a feature on the ground is still discernible on the image/photo 1 resolution photoscale s p smallest detail
- 21. Smallest detail and resolutionExample: The smallest detail that needs to be seen on the photograph is 1 foot in length. If the resolution of the photo is 0.1 mm, determine the photoscale.
- 22. Smallest detail and resolutionSolution: 1 photoscale 3000
- 23. C-factor and desired minimum contour interval• Contour interval – difference in elevation between consecutive contour lines flying height H C factor contour interval h• C-factor range from 1200 to 1500
- 24. C-factor and desired minimum contour intervalExample: The C-factor of the instrument is given to be 1500. If the desired contour interval is 1 meter, determine the photoscale.
- 25. C-factor and desired minimum contour intervalSolution: 1 photoscale 9000
- 26. Expected AccuracyMean square error of horizontal position of points: mh 0.1 H 0.0001H 10-4 H%ο – per mil; equivalent to 1/1000For Cadastral Survey: mh = 10 cm (urban) = 30 cm (rural)
- 27. Expected AccuracyExample: Determine the photoscale for an urban area if the camera to be used is a wide-angle camera.
- 28. Expected AccuracySolution: 1 photoscale 6000
- 29. Enlargement from photo to map• Using the stereoplotter, there will be an enlargement from the photo to the stereomodel: Z enlargement Cwhere: Z = projection distance for stereoplotter C = f = projection distance of camera
- 30. Enlargement from photo to mapExample: A map with scale 1:5000 was derived from a stereomodel with a scale of 1:8000, using a stereoplotter. The projection distance of the stereoplotter is twice the focal length of the camera. Determine the scale of the photograph that was used to generate the stereomodel.
- 31. Enlargement from photo to mapSolution: 1 photoscale 16000
- 32. END OF LECTURE

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