of each target is a small fraction (about one third) of the 
time required to read an equivalent set of images on ten 
separate frames). 
(f) Because successive images of a multiply exposed target are 
physically close together and would be measured in rapid 
succession, their film coordinates would largely share any 
uncompensated systematic errors. This could be expected to 
Lead to triangulated X,Y,Z coordinates in which relative 
systematic errors of successive targets are virtually non- 
existent. Accordingly, extraordinary accuracies become 
possible insofar as detection of change is concerned, as, 
for example, when successive observations are made of an 
object undergoing thermal deformation. 
(g) If a given camera is perfectly stable in exterior orientation 
throughout a series of multiple exposures recorded in the 
incremental film-shifting mode, and if fiducial marks are 
recorded for each exposure, all such exposures can be con- 
strained in STARS software to share common exterior projec- 
tive parameters. Alternatively, if significant changes in 
angular elements (o,w,k) are suspected, the exposure can be 
constrained to share only translational elements (X ,Y ,Z ). 
In either case the result is an appreciable strengthening of 
the photogrammetric adjustment. | 
(h) If the multiply exposed object considered under (g) is also 
stable throughout the series of exposures, STARS software 
can be exercised to effect a succession of least squares 
transformations (translations/rotations) to combine all of 
the separate sets of images into an equivalent single set. 
(2) With retroreflective targets exposures can be made so that 
only the targets themselves are recorded on the film. How- 
ever, occasions arise where is is desirable to record the 
object also, perhaps as a faint 'phantom' image. This can 
be accomplished if supplementary illumination, not emanating 
from the camera, is available. Then, a sufficiently long 
exposure can be made by means of the camera shutter to bring 
out the background to whatever extent is desired. 
(j) When a large object or structure must be photographed from 
a considerable distance in daylight, some areas of interest 
may be in full sunlight and others in deep shadow. This can 
present an extremely difficult photographie Lighting problem 
when conventional targets are employed, for fill-in illumina- 
tion must be comparable in intensity to sunlight. With retro- 
reflective targets, on the other hand, all necessary illumination 
is provided by a single, relatively low powered flash unit 
Located close to the camera, and targets in sunlight and shadow 
all end up equally well exposed with clear backgrounds. 
The above by no means exhausts the possibilities opened up by the use of 
retroreflective targeting in conjunction with instrumentation and software 
specifically designed to exploit its characteristics. A fuller exposition 
is to be found in Brown (1980). Although designed for optimal utilization 
of retroreflective targeting, STARS by no means neglects situations in 
which conventional targeting is employed. 
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