U SA —6 PHOTOGRAMMETRIC ENGINEERING 
PLOTTERS EMPLOYING PAPER PRINT PHOTOGRAPHS 
Following construction of a control base the student learns to transfer 
planimetric detail by applying the various optical transfer devices such as the 
sketchmaster. Later, more elaborate plotting devices are demonstrated; these 
instruments make use of photographic prints and have come to be known as the 
"paper-print'" instruments. Some examples of these instruments are the Kail, 
KEK, and Mahan plotters. These instruments are useful for certain types of 
work, although considered less accurate than the double-projection instruments. 
They are sometimes used as transfer devices enabling one to transfer geologic 
detail, identified on the photographs, onto a topographic base. 
GRAPHIC METHODS 
The sections of the course dealing with graphic methods of using aerial photo- 
graphs have been found to be very useful since a geologist spends much time in 
the field with his notebook and aerial photographs only. Graphic methods, also, 
are another means for teaching the fundamentals and demonstrating how 
theoretical principles can be applied to extracting useful information from verti- 
cal, oblique and terrestrial photographs. A knowledge of graphic methods in- 
creases one’s self-reliance and can be used to solve many of the problems with 
simple tools when the more elaborate ones are not at hand. Some typical ex- 
amples of the graphic methods are extraction of vertical and horizontal angles 
from oblique and terrestrial photographs, and how they are used to obtain po- 
sition of features and their elevation. 
OBLIQUE PHOTOGRAPHS 
Some instruction is given in the theory and use of oblique photographs and 
the photoalidade. Oblique photography, an outgrowth of the need for aeronauti- 
cal charting on a worldwide basis, is still used in reconnaissance work, and 
remains a special interest of our Alaskan Geology Branch. Oblique photographs 
present a comprehensive view of the terrain and enable a geologist to tie 
together many geologic details over a wide area. Their greatest value lies in 
displaying physiographic, geologic, and geographic features in natural perspec- 
tive, and they can be studied under the stereoscope, facilitating reconnaissance 
geology and the planning of field work. In order to obtain a better understand- 
ing of the basic principles of photogrammetry, some instruction is given in the 
photoalidade. Photoalidade work is very similar to planetable and alidade work 
in the field. Vertical and horizontal control can be extended by photoalidade 
means; sometimes it is an only means for establishing control in remote, inac- 
cessible regions. 
NEWER PHOTOGRAMMETRIC TECHNIQUES 
The training course is most effective for conveying information of some of 
the newer techniques of photogrammetry that can be applied to the geologist’s 
problems. One of the common problems is that of transferring field geology 
from photographs to the topographic base map. Fundamentally, this particular 
problem concerns the differences between the perspective of the aerial photo- 
graph and the orthographic characteristics of the map. The geologist has 
already learned to solve this problem by means of stereoscopic plotting instru- 
ments or by means of new techniques developed under the auspices of the 
Interdivision Committee. 
One of the methods developed as a result of geologic interest in photo- 
grammetry is the stereo-plotted grid, a systematic means for organizing the 
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