NEW DEVELOPMENTS IN ORTHOPHOTOGRAPHY 1 
By 
Marvin B. Scher 
U.S. Geological Survey 
Abstract 
The considerable amount of research and development in orthophotography 
that has occurred in the past few years accurately reflects the promise of 
this new product. Since the 1960 meeting of the International Society for 
Photogrammetry, significant changes have been made in the Orthophotoscope 
as designed in the research laboratories of the U.S. Geological Survey. 
Much attention has been given to improving the techniques for preparing 
orthophotographs, orthophotomosaics, and orthophotomaps. Studies are con 
tinuing to determine effective mapping applications of orthophotographs. 
The reaction of the map-using public to orthophotomaps is being closely 
observed. 
Orthophotoscope Modifications 
At the Ninth International Congress on Photogrammetry in London 4 years 
ago, Roland H. Moore of the U.S. Geological Survey described the U-60 Ortho 
photoscope (fig. 1). This instrument, like two earlier ones,2 was designed 
to convert perspective photographs into equivalent orthographic photographs. 
The latest U.S. Geological Survey Orthophotoscope, designated model T-64, 
combines features that were considered beneficial on earlier versions of 
the instrument with innovations that operational experience has indicated 
would be advantageous. Retained are such major features as (1) the self 
synchronizing mechanisms used to transmit x-, y-, and z-motions to the 
scanning assembly and (2) the capability for simultaneous or subsequent use 
of the profile data from each scan to operate other image-restitution equip 
ment or to extract hypsometric information in digital or analog form. 
In the T-64 Orthophotoscope (fig. 2), scanning is done in the y direc 
tion and an automatic stepover occurs at the end of each scan. Design 
changes permit the selection of almost any scan width up to 25 millimeters. 
The amount of stepover can be controlled to an accuracy of approximately 
25 microns, thereby affording excellent control over the correlation be 
tween the stepover and the width of the scan. This close control is expected 
to prevent scanning tracks, caused by minute exposure voids and overlaps 
between adjacent scans, from registering on the orthonegatives. 
The new instrument has a flat film-supporting platform rather than the 
cylindrical drum used in the 1960 Orthophotoscope. The principal objective 
of the cylindrical design was to provide the operator with a better view 
of the model and to reduce the fatigue experienced with earlier instruments. 
However, operational research indicated that the drum-type instrument re 
quired several critical mechanical adjustments that are not necessary when 
a flat platform is used to support the orthonegative. Because the geometric 
fidelity of the orthophotograph depends directly upon the precision with 
which the scanning aperture is kept in contact with the apparent model 
^Publication authorized by the Director, U.S. Geological Survey, 
Washington, D.C. 
2 
Bean, R. K., and Thompson, M. M., 1957, Use of the Orthophotoscope, 
Photogrammetric Engineering, Vol. XXIII, No. 1, p. 170-179.