Remote Sensing and GIS Application Lecturer Ruba Yousif
Remote Sensing and GIS Application Lecturer Ruba Yousif Hussain Third Year 1
Remote Sensing and GIS Application Third Year Lecturer Ruba Yousif Hussain Basic Principal of Photogrammetry is the science of measurements from aerial photographs. making Vertical photographs Photographs taken from an aircraft with the optical axis of the camera vertical or as nearly vertical as possible. Scale On a map, scale is everywhere uniform because a map is an orthographic projection. An aerial photograph, is a perspective projection and its scale varies with variations in terrain elevation. 2
Remote Sensing and GIS Application Third Year Lecturer Ruba Yousif Hussain Figure 1 Geometry of a vertical photograph 3
Remote Sensing and GIS Application Third Year Lecturer Ruba Yousif Hussain (a) Map (orthographic projection) Constant scale No relief displacement (b) Photo (perspective projection) Varied scale Relief displacement Figure 2 4
Remote Sensing and GIS Application Third Year Lecturer Ruba Yousif Hussain Scale of a Vertical Photograph over Flat Terrain The ratio of the photo distance ab to the corresponding ground distance AB. That scale may be expressed in terms of camera focal length f and flying height above ground H'. Figure 3 Two dimensional view of a vertical photograph taken over flat terrain. Example 1 A vertical aerial photograph is taken over flat terrain with a 6 in (152. 4 mm ) focal length camera from an altitude of 6000 ft above ground. What is the photo scale ? Solution 5
Remote Sensing and GIS Application Third Year Lecturer Ruba Yousif Hussain Scale of a Vertical photograph over Variable Terrain The scale at any point whose elevation above datum is h may be expressed as For vertical photographs taken over variable terrain, there an infinite number of different Scales. This is one of the principal differences between a photograph and a map. Average Photo Scale 6
Remote Sensing and GIS Application Third Year Lecturer Ruba Yousif Hussain Figure 4 Scale of a vertical photograph over variable terrain. 7
Remote Sensing and GIS Application Third Year Lecturer Ruba Yousif Hussain Example 2 Suppose that highest terrain h 1, average terrain haverage, , and lowest terrain h 2 , of Figure 4 are 2, 000, 1, 500, and 1, 000 ft above mean sea level, respectively. Calculate maximum scale, minimum scale, and average scale if flying height above mean sea level is 10, 000 ft and camera focal length is 6 in (152. 4 mm). Solution Maximum scale occurs at maximum elevation Minimum scale occurs at minimum elevation Average Scale 8
Remote Sensing and GIS Application Third Year Lecturer Ruba Yousif Hussain Example 3 A camera equipped with a 152 mm focal-length lens is used to take a vertical photograph from a flying height of 2780 m above mean sea level. If the terrain is flat and located at an elevation of 500 m, what is the scale of the photograph? Solution Example 4 Assume a vertical photograph was taken at a flying height of 5000 m above sea level using a camera with a 152 mm focal length lens, (a) Determine the photo scale at points A and B, which lie at elevations of 1200 and 1960 m. (b) What ground distance corresponds to a 20. 1 mm photo distance measured at each of these elevations? Solution a- b- 9
Remote Sensing and GIS Application Third Year Lecturer Ruba Yousif Hussain Example 5 The horizontal distance AB between the centers of two street intersections was measured on the ground as 1320 ft. The corresponding line ab appears on a vertical photograph and measures 3. 77 in. What is the scale of the photo at the average ground elevation of this line? Solution Photographic scale can then be calculated from the following equation: Example 6 On a vertical photograph the length of an airport runway measures 6. 30 in. On a map which is plotted to a scale of 1: 24, 000, the runway scales 4. 06 in. What is the scale of the photograph at runway elevation? Solution 10
Remote Sensing and GIS Application Third Year Lecturer Ruba Yousif Hussain Example 7 Assume that two road intersections shown on a photograph can be located on a 1 : 25000 scale topographic map. The measured distance between the intersections is 47. 2 mm on the map and 94. 3 mm on the photograph, (a) What is the scale of the photograph? (b) At that scale, what is the length of a fence line that measures 42. 9 mm on the photograph? Solution ab- 11
Remote Sensing and GIS Application Third Year Lecturer Ruba Yousif Hussain Ground Coordinates from a Vertical Photograph Figure 5 shows a vertical photograph taken at a flying height H above datum. Images a and b of the ground points A and B appear on the photograph, and their measured photographic coordinates are xa , ya , xb , and yb. The ground coordinates of points A and B are XA , YA , XB , and YB. The horizontal length of the line AB can be calculated The horizontal angle APB may be calculated as 12
Remote Sensing and GIS Application Third Year Lecturer Ruba Yousif Hussain Figure 5 Ground coordinates from a vertical photograph 13
Remote Sensing and GIS Application Third Year Lecturer Ruba Yousif Hussain Example 8 A vertical aerial photograph was taken with a 6 -in (152. 4 mm ) focal-length camera from a flying height of 4530 ft above datum. Images a and b of two ground points A and B appear on the photograph, and their measured photocoordinates (corrected for shrinkage and distortions ) are xa= -52. 35 mm , ya = - 48. 27 mm , xb = 40. 64 mm , and yb = 43. 88 mm. Determine the horizontal length of line AB if the elevations of points A and B are 670 and 485 ft above datum, respectively. Solution 14
Remote Sensing and GIS Application Third Year Lecturer Ruba Yousif Hussain Endlap and Sidelap The overlap provides coverage of the entire ground area from two viewpoints, such coverage being necessary for stereoscopic viewing and measuring. Figure 6 End lap of photographs in a flight strip. Figure 7 Side lap of adjacent flight strips. 15
Remote Sensing and GIS Application Third Year Lecturer Ruba Yousif Hussain End lap Side lap 1. Common area covered by two adjacent successive photos of the same flight lines / strips or strip 2. Usually 60 % ± 5 % 2. About 25 -30 % ± 10 % (generally 30 % ) The ground distance between the photo centers at the times of exposure is called the air base. The ratio between the air base and the flying height above ground determines the vertical exaggeration perceived by photo interpreters. The larger the base-height ratio, the greater the vertical exaggeration. Uses of Photogrammetry 1. topographic mapping 2. highway planning and design 3. geologic maps 4. traffic management 5. military intelligence 16
Remote Sensing and GIS Application Third Year Lecturer Ruba Yousif Hussain Area Measurement Example 9 A rectangular agricultural field measures 8. 65 cm long and 5. 13 cm wide on a vertical photograph having a scale of 1: 20000. Find the area of the field at ground level. Solution Ground area = 1730 m × 1026 m = 1774980 m 2 Example 10 The area of a lake is 52. 2 cm 2 on a 1: 7500 vertical photograph. Find the ground area of the lake. Solution 17
Remote Sensing and GIS Application Third Year Lecturer Ruba Yousif Hussain Relief Displacement Figure 8 Geometric components of relief displacement 18
Remote Sensing and GIS Application Third Year Lecturer Ruba Yousif Hussain Expressing distances D and R at the scale of the photograph, we obtain Rearranging the above equation yields where d = relief displacement r = radial distance on the photograph from the principal point to the displaced image point h = height above datum of the object point H = flying height above the same datum chosen to reference h Example 11 For the photo shown in Figure 8 , assume that the relief displacement for the tower at A is 2. 01 mm , and the radial distance from the center of the photo to the top of the tower is 56. 43 mm. If the flying height is 1220 m above the base of the tower, find the height of the tower. Solution 19
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