May, 1960 Commission II 179 
model is observed. The instrument has a floating mark that seems to move in three- 
dimensional space. The oblique photographs form a plane in this space, and when the 
floating mark is in this plane, the corresponding points in the two photographs will 
coincide with the measuring mark. 
The Straight Line Plotter has two photocarriers that may be shifted separately in 
two directions (x and y) in the horizontal plane, and rotated independently about the 
vertical axis. Both carriers may also be shifted together in the direction of one of the 
axes. These two motions make it possible to set the two photographs in required 
positions relative to each other, and their common motion will represent a straight line. 
Thus, the straight line is not scribed on the emulsion, but is preserved on vertical 
photographs by identifying points through which the line passes. Scribing is also 
possible and is used to mark line positions on the outer edges of the diapositives. These 
markings are useful when a re-check is required. 
ANALYTICAL PLOTTER 
A new principle for the design of photogrammetric plotters has been developed 
by Mr. U. V. Helava of the Photogrammetric Research Section of the National 
Research Council. According to the new principle, the conventional optical or 
mechanical projection is replaced by a mathematical formulation executed by an 
electronic computer using appropriate servo mechanisms. Consequently the photo- 
graphs are not tilted, but are shifted in their plane to bring the image point to its 
required position. 
  
Fic. 2. Photograph of a miniature model of the projected Analytical Plotter 
The new principle presents numerous advantages and widens the field of problems 
that may be solved by photogrammetric means. Simple mechanical construction, 
movability, improved accuracy, versatility, and suitability for automation are some of 
the advantages. Because geometric problems are solved numerically by a mathematical 
formulation, images other than strict central projections may be used for plotting 
purposes, and various mathematical methods may be adopted to manipulate source 
data. The plotter can also accept numerical data from outside. 
The plotter has two main parts: (a) the viewing-measuring device and (5) the 
computer. ‘These two parts are interconnected to form a feed-back loop through the 
operator. The XY co-ordinates from the viewing-measuring device and a computing