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ABSTRACT 
DEMONSTRATION OF SELECTED ASPECTS OF 
A UTILITY MAPPING SYSTEM (UMS) 
by 
Dean Merchant, Topo Photo, INC. 
Robert Tudhope, Ontario Hydro 
Mapping power distribution lines presents a unique 
photogrammetric challenge. The homogeneous character of a power 
cable precludes the identification of conjugate imagery in the 
photo-base direction when photography is flown in the direction of 
the. power line. By locating small, digital array cameras in the 
wing tips of low flying aircraft, the error in image identification 
occurs in the cross-base direction (y-parallax) and does not 
present a problem in computing conjugate ray intersections for 
measurement of elevation and horizontal position normal to the 
direction of the cable. A program of research was sponsored by 
Ontario Hydro of Toronto to test this "cross-base" concept for 
power line surveys. Results indicate that the cross-base concept 
is feasible and can meet required spatial accuracies provided care 
is taken in providing strong geometry and calibrating the 
photogrammetric system in the air. Requirements by utilities for 
spatial accuracy on cables, towers and insulator attach points are 
described. Results obtained from flight tests are presented. 
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