Photogrammetry amir

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  • 1.Muhammad Amir FaheemUllah Khan Saddam Hussain Faisal Khan(On leave) Instructor :Engr. AfedUllah Khan

2. The science of obtaining information about an object by acquiring data with a device which is not in direct contact with that object. 3. photo = "picture, grammetry = "measurement, therefore photogrammetry = photo-measurement Photogrammetry is the science or art of obtaining reliable measurements by means of photographs.4 4. a.Arial using photographs taken from the air or from space with the camera usually pointing vertically downwards 5. Vertical aerial photographs are taken along parallel passes called flight strips. Successive photographs along a flight strip overlap is called end lap 60%Area of common coverage called stereoscopic overlap area.Overlapping photos called a stereopair.7 6. AerialTerrestrialOblique VerticalLow oblique (does not include horizon)Truly Vertical High oblique (includes horizon)Tilted (1deg< angle < 3deg)9 7. Position of camera at each exposure is called the exposure station. Altitude of the camera at exposure time is called the flying height. Lateral overlapping of adjacent flight strips is called a side lap (usually 30%). Photographs of 2 or more side lapping strips used to cover an area is referred to as a block of photos.10 8. Radial line method :-This method can be used if three points in each photograph are known. The first step is to determine the scale of the photograph. This is obtained from the ratio of the distance between two points on the photograph and the distance between them on the ground. 9. Two points chosen for scaling should lie nearly equidistant on either side of the principle point. A map is drawn to this scale and all the ground points are plotted on it 10. Terrestrial surveying is also referred to as field or ground-based surveying. It can be defined as the art and science of taking measurements on or near the surface of the earth. 11. The terrestrial photographic surveying considered as the further development of plane table surveying 12. The principle of this method is exactly similar to that of plane table surveying The position of an object with reference to the base line is given by the intersection of rays drawn to it from each end of the base line 13. The main difference between plane table and terrestrial survey is In plane tabling most of the work is executed in the field while in terrestrial surveying it is done in the office. 14. Field work of terrestrial photogrammetry consist of Reconnaissance Triangulation Camera work 15. The preliminary vision or inspection of an area to be surveyed. 16. The control is established by triangulation All camera station should be connected by a triangulation system The elevation of the camera station should be determined by the direct or trignometrical levelling 17. The photographs are taken in pair from the end of the base line such that a line joining the camera station which is carefully measured 18. This method is the modern development of photographic surveying. It consists of taking stereoscopic views of the surface features in pairs at the end of a base line. 19. The two exposures(photos) must be made with the photographic plates in the same vertical plane. This can be done by taking two photographs at 90 angle to the base line. 20. Horizontal distance between parallel principle is usually between 30 meter and 120 meter. 21. Pixel is derived from the combination of two words: Picture and element. Pixel is the smallest building block of a picture. If the resolution is high, the pixels are many than in low resolution. 22. Vector images are made up of basic geometric shapes such as points, lines and curves. The relationship of the shapes is expressed as a mathematical equation which allows the image to scale up or down in size without losing quality. 23. Raster images are made up of a set grid of dots called pixels where each pixel is assigned a color value. Unlike a vector image, raster images are resolution dependent. When you change the size of a raster image, you shrink or stretch the pixels themselves which can result in a significant loss of clarity and very blurry image. 24. a.Topographical Mapping The plotting of map detail and contours is normally carried out using aerial photogrammetric methods These methods are used for both original survey and revision, and replace classical ground methods except where the task is so small that flying is uneconomical The technique needs a certain amount of ground surveyed control, but this requirement is being continually reduced with the improvement of aerial triangulation techniques to provide supplementary control. A final Field check is necessary 25. b.Large Scale Plans Large scale surveys can be produced accurately and quickly by air survey methods, but require more field checking in addition to the provision of ground control For large tasks, such as road building and major constructions, air survey methods are quicker and cheaper than ground methods Profiles for determination of earthwork quantities and other data useful to Civil Engineer may be simply obtained from the same photographs 26. c. Cadastral Plans Similar advantages may be gained by an air survey for cadastral purpose as are provided in the production of large scale plans. As the accuracy of the cadastral plan is related to the value of land, the traditional ground method trends to be slower, costly but very accurate In most cases, the accuracy of a well planned air survey is sufficient for cadastral purposes, and this method is used in many countries Where boundaries are related to described features, or land is very valuable, the additional accuracy of ground survey may be necessary 27. d. Land use maps Air survey techniques may be used not only to define the extent of an area, but also to identify its use and measure the yield of a crop Forestry is a typical application where, by plotting the limits of timber and measuring tree heights, an accurate estimate of yield may be given. The use of special films, such as color and infra-red will provide additional information about the quality of the crop 28. e. Hydrographic Maps and Charts Air survey techniques are particularly valuable in the accurate plotting of coastlines, sandbanks and small islands where the changing tide is a problem for ground methods The use of special film will again add more information, either by clearly delineating water limits or by extra penetration in shallow water 29. f. Exploration and Reconnaissance Information may be gained about areas to which access is restricted by employing air survey techniques In the case of military reconnaissance, a high flying or unmanned aircraft can obtain photograph that will provide data for an accurate survey For explorers, and area can be mapped before the first entry, either from photographs obtained by aircraft as in the case of Moon or Mars, or by specially equiped satellites 30. g. Terrestrial, Industrial and Scientific Uses Photogrammetry has provided rapid, accurate and in some cases unique solutions to many non topographical problems. The following are of particular interest 1.Detailed Survey of Historic Buildings Precise plans of building facades and architectural detail may be obtained without direct measurement by terrestrial photogrammetric techniques 31. 2. Traffic Accidents Terrestrial methods are also used to record details of accidents in some countries This allows obstructions to be cleared without delay, the scene being plotted at a later stage3. Medical Applications Short range photogrammetry is in use by doctors and dentists to define conditions requiring treatment and also to study the results of treatment 32. 4. Analysis of movement Tidal and Particle movement may be analyzed by photogrammetric methods by taking photographs of the moving surface with a fixed camera The stereo model obtained shows vertical relief proportional to the amount of movement contours may be plotted 33. DEDICATED TO MY MISTAKES