Part 6 



PIIOTOGRAMA/LETRIC EVALOATION OF PROJECT SWOP 



Introduction 



Aerial photogrammetry is the science of obtaining reliable lioriiaontal 

 and vertical measurements of all unobscured natural and maxi-rnade features 

 appearing in aerial photographs o Since the aerial photograph is a detailed 

 and permanent record of a given section of the earth's surfaces it furnishes 

 more completely than any othar ineans the information required in the pre- 

 paration of maps E.nd chartSo Geometricallyj, all photographs are perspec- 

 tive views and all maps are orthographic views of the earth's surface. 

 The science of aerial photogrartiixietry is used, to convert the perspective 

 views of tlie aerial photographs into the orthographic view of a maps and 

 also to record properly all the photographed information into a true map 

 presentation. 



For regular photograrnnietric mapping purposes^ a.eriai photography 

 obtained with the camera optical axis vertical, is accomplished in such a 

 manner th£.t there is approximately 60 percent overlcip betv^^een photographs 

 in lime=of=£Lightj and approxim.ately 30 percent sidelap between adjacent 

 strips of pliotographSo The 60 percent overlap provides at least two differ- 

 ent views of all features photographedg and is necessary to achieve the 

 stereoscopic effect by which interpretation and measurements may be 



accoraplishedo 



40 



