ANALYTICAL ON-LINE SYSTEMS IN CLOSE-RANGE PHOTOGRAMMETRY
tally formed in the computer memory as an
equivalent to the analog model in the analog
systems. Let us call it a virtual model. The
source of control is denoted by a double circle
and control outputs by single circles properly
positioned with respect to relevant boxes.
Individual directed lines show the control
flow. The control is described for system
functions in both the orientation and final
operation phases.
The practical difference between off-line
and on-line systems is obvious from the way
in which the operation control can be ef-
fected. In closed-loop on-line systems the
control originates from the model space with
an instantly enforced proper positioning of
photographs, thus fully eliminating any
stereoscopic disparities in the observed
three-dimensional optical model. In off-line
systems, however, the control is confined
only to the two-dimensional space of photo-
graphs. Because ofthe missing feedback from
the model to the photo space, the observed
stereoscopic model must be steadily adjusted
by manual corrections and the data cannot be
collected in sequences related to the three-
dimensional coordinate system of the model.
BASIC CHARACTERISTICS OF ON-LINE
ANALYTICAL SYSTEMS
From the operational point of view there
ON-LINE ANALYTICAL SYSTEMS
Virtual Graphical Digital
Photo modet modet object
LEGEND:
mode
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contretted by
Closed-Loop
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Orientation
Compilation
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tems.
Control flow in photogrammetric sys-
83
are three basic phases in the process of an
on-line analytical operation:
€ definition of the image geometry,
€ reconstruction of the photogrammetric
model, and
e detailed photogrammetric compilation of
the model.
The first two phases are preparatory and ac-
tually proceed in an off-line mode, whereas
the final phase is a typical realtime operation
fully dependent on the use of the computer
feedback control.
In defining the image geometry one actu-
ally chooses from existing models by determin-
ingthe type of general conditions, and further
specifies the characteristics of the image by
its interior orientation and distortion
parameters. Obviously, the image geometry
essentially affects the process in the follow-
ing operational phases. The reconstruction of
a photogrammetric model results in a good
description of relations between the images
and the object by means of the parameters of
exterior orientation. The reconstruction
phase includes a one-step collection of meas-
ured data and usually an iterative solution of
the parameters. The compilation phase rep-
resents an operation appearing practically
continuous even though it is simulated by a
fast repetitive cycle of digital computations.
These proceed in a stream of densely spaced
discrete data points defined by the operator's
control of the floating mark in the observed
optical model. In general, this computation is
based on transformations between the model
and image spaces with the use of all previ-
ously derived parameters of interior and ex-
terior orientation. Included in the computa-
tions are corrections for any image distor-
tions. The output from the photogrammetric
compilation can be presented in an analog
form on a plotting table or on a CRT screen,
and in a digital form by coordinate readouts
and printed listings. If the output is stored in
the computer memory, numerous pos-
sibilities are available for further editing and
additional processing of data, including their
display in the form of computer-generated
graphics. The physical control ofthe compila-
tion process can be arranged or programmed
in many different ways ranging from manual
through mixed to fully automated computer
control. In the mixed mode partial control
drive is generated by the computer and addi-
tional necessary changes or adjustments are
then continuously introduced by the
operator.
The main advantage of the on-line analyti-
cal processing is that it allows for an im-
mediate and useful man-machine interaction
