o capability to mathematically correct for virtually 
any undesirable image displacement, 
o high-accuracy instrument design coupled with  mathe- 
matical corrections for residual instrument errors, 
o no limitations on principal distances and other came- 
ra characteristics, 
o on-line collection and processing of digital data, 
o real time data checking, 
"user friendly" for operation by nonphotogrammetrists. 
Oo 
HYBRID STEREOPLOTTERS 
Instruments such as the Wild B-8 (fig. 3) and Kelsh 
stereoplotters are "conventional" compilation instruments 
originally designed for mapping that have been fitted with 
computers to produce "hybrid instruments" for both digital 
and graphic compilation. Although, some of these instruments 
still have limitations, such as restrictions on principal 
distances, corrections can be made for complex errors, 
stereomodels can be "warped" to fit control, and data can be 
edited "on-line" before a stereomodel is disassembled. Some 
have provisions for computer refined relative orientation 
and many of the other capabilities found in a conventional 
analytical stereoplotter. 
ANALYTICAL MONOCOMPARATORS 
Monocomparators (fig. 4) are used to measure the photo- 
coordinates of discrete image points. The photocoordinates 
of all points involved are measured with the monocomparator, 
a mathematical stereomodel is formed, the stereomodel is 
fitted to measured control points, and the coordinates of 
all other measured points of interest are computed. In some 
cases a preliminary check of the data is made by doing a 
preliminary computation before a plate is removed from the 
comparator. 
Some advantages of analytical monocomparators are: 
o automatic drive from point to point where they are in 
a known pattern 
o automatic setting and measuring capabilities when 
equipped with target-recognition devices 
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