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them as problems of Collocation (Moritz 1978) in terms of prediction and 
filtering of noise and signals. 
With the advent of the analytical plotters in the early 1960s came 
the concept of on-line solutions (Cunietti et al 1964). However, .with 
regard to on-line aerotriangulation people found that sequential procedures 
are comparatively more cost-effective than the simultaneous solution at an 
analytical plotter (Strahle 1971, Hobbie 1978). The block formation with 
least squares adjustments can be also achieved with success in such ap 
proaches (Dorrer 1978). 
6.2.4 Unconventional Technologies and Advancements 
Man's involvement in space and international conflicts like World 
War II, Korean and Vietnam wars brought about certain technological de 
velopments in imaging systems and data processing procedures. These posed 
tremendous challenges in photogrammetry. Initially some of the pertinent 
studies were necessarily classified. However, apart from unconventional 
applications of analog and conventional photogrammetry, innovations and 
procedural developments in analytical photogrammetry occurred which deserve 
mention here. Such developments have been noticed during the 1960s and 
later. 
Case (1967) demonstrated how the standard collinearity equations 
can be modified to handle some panoramic and strip photographic systems. 
Recent advancements indicate subsequent supportive researches related to 
various unconventional imaging systems (Masrv 1969, Derenvi 1973, Clerici 
1977, Kratky 1983, Ghosh 1975, Takamoto 1976 are some typical examples). 
However, apart from such adaptations of analytical photogrammetry to uncon 
ventional technologies and systems one can notice two distinct areas of new T 
thinking and development viz., (a) Digital Terrain Models (DTM) and (b) 
Real Time Photogrammetry, which deserve particular attention here. 
6.2.4.1 Digital Terrain Models (DTM) 
The DTM concept had its origin in the work performed by Charles L. 
Miller (1957) and his associates at the Massachusetts Institute of Technol 
ogy in the USA. The objective was first to expedite highway design by 
digital computation based on photogrammetricallv obtained terrain data in 
three-dimensions. 
Eventually, the concept has been developed by considering ordered 
arrays of numbers that represent the spatial distribution of terrain 
characcteristics. In the most usual case, the spatial distribution is rep 
resented by X and Y (planimetric) coordinates and the terrain character 
istic, is recorded as the terrain elevation, Z. Recent literature (ASP 
1978) has referred to these and other distributions (like latitude, lon 
gitude and elevation) as Digital Elevation Models (DEM) to distinguish 
them from other models which describe different terrain characteristics. 
The data are also organized as equations of surface defined by polynomials 
or Fourier series. One may note also that characteristics other than mere 
elevation, such as terrain slope, land value, ownership, land use or soil 
tvpo, may also be included in the DTM (Doyle 1978). The distribution of 
points and their coordinates required in the process of digitizing are not