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GEOG 2420 (3)
Chapter 6

Geog 2420 Chapter 6

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University of Guelph
GEOG 2420
John Lindsay

Geog 2420 Chapter 6 Photogrammy Jenson is the art and science of making accrue measurements by means of aerial photographyanalog photogrammy is performed using data that are in hard copy formatdigital photogrammy is performed using a computer and digital aerial photography these measurements can be obtained from a single vertical aerial photograph usingphotogrammyscale of photographobject heightobject lengtharea of an objectperimeter of an objectgreyscale tone or color these quantitative measurements can be made using multiple stereoscopic aerialphotographs and stereoscopic parallaxprecise planimetric object location of building footprints streets and shorelinesprecise object height z Flightlines of Vertical Aerial Photographya flightline of vertical photography is obtained by mounting a camera to an aircraft andobtaining photographs of terrain directly beneath the platform at specific exposure stations the time between individual exposures along a flightline is determined by setting the cameraintervalometer the aerial photographer takes into account the speed of the aircraft and the scale desired and sets the intervalometer so that each vertical aerial photograph overlaps the next by about60 this overlap is important as it provides at least 2 or 3 photographic views of each object in thereal world most aerial photography projects require multiple flightlines when this occurs the flightlinesnormally overlapped 2330 called the side lapmultiple flightlines with 2030 side lap are referred to as a block it is possible to combine several vertical photographs in the block of photography to create anuncontrolled photomosaic most aerial photography acquired each year is obtained in the early spring leaf off periodwhen snow is not present and deciduous trees are still dormant makes t easier for the image analysts to see through branch of the canopy to the groundsurface Fiducial Marks and Principal Points drawing a line between opposite fiducial points locates the principal point of the photograph which is the exact point on earth where the optical axis of the camera was pointing during theinstant of exposurethe transferred principal point is called conjugate principal point the actual line of flight can be determined by laying out the photography and drawing a linethrough the principal point and conjugate principal points
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