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# Ge 178 lecture 5 (principles of aerial photography)

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### Ge 178 lecture 5 (principles of aerial photography)

1. 1. GE 178 Lecture 5:Principles of Aerial Photography andPhoto Scale Determination
2. 2. Aerial Photo (Image) vs Map• Images central projection, non-uniform scale actual features• Maps orthogonal projection, uniform scale symbols
3. 3. Orthogonal vs Perspective Projection
4. 4. Orthogonal vs Perspective Projection
5. 5. Orthogonal vs Perspective Projection
6. 6. Orthogonal vs Perspective Projection
7. 7. Vertical Photography
8. 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. 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. 10. Elements of a Vertical Photograph
11. 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. 12. Fiducial Marks and Principal Point
13. 13. Fiducial Marks
14. 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. 15. Three Photo Centers Ground PPoint Isocenter Nadir
16. 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. 17. PhotoScale
18. 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. 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. 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. 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. 22. Smallest detail and resolutionSolution: 1 photoscale  3000
23. 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. 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. 25. C-factor and desired minimum contour intervalSolution: 1 photoscale  9000
26. 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. 27. Expected AccuracyExample: Determine the photoscale for an urban area if the camera to be used is a wide-angle camera.
28. 28. Expected AccuracySolution: 1 photoscale  6000
29. 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. 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. 31. Enlargement from photo to mapSolution: 1 photoscale  16000
32. 32. END OF LECTURE