LR-1 Portable Line-Drawing Rectifier
B. FORREST
P.
R.
D. P. HATTAWAY
The Bendix-developed LR-1 portable line-drawing rectifier produces rectified line
drawings of selected images on tilted aerial photographs. The entire system consists of
two compact modules which can be placed on an office desk or table. In operation,
the operator traces features of interest on the tilted photograph, and a stylus simul-
taneously draws the rectified feature at the desired scale. Focal lengths from 8 centi-
meters to 1 meter and camera tilts greater than 80° can be accommodated.
INTRODUCTION
Optical rectifiers permit viewing and rectification
of all photographic image points simultaneously. This
parallel processing of image data has obvious advan-
tages for many purposes. However, optical rectifiers
are rather massive instruments and are quite limited
in the camera geometry and photographic tilts that
can be accommodated.
Many current mapping problems call for a differ-
ent kind of rectification than performed with the
optical rectifiers. Entire photographs need not be
rectified, only the outlines of selected photo images.
The input photographs may have unusual camera
geometry and large tilts. Speed of operation and port-
ability may be important considerations, particularly
for military use.
A new kind of device was developed to meet these
requirements: the LR-1 line-drawing rectifier.* This
instrument is actually a form of single-photograph
plotter. In principle, the line rectifier mathematically
processes one point on the photograph at a time. This
mathematical point-by-point processing eliminates
restrictions on the camera tilt and geometry that can
be accommodated; however, the individual points are
processed rapidly enough for a continuous line to be
rectified and plotted without visible gaps. In opera-
tion, the user traces desired photo images by moving
a projected measuring mark over the surface of the
photograph. The rectified and scaled path of the mea-
suring mark is simultaneously plotted on a manu-
script. Electronic analog computers are well suited to
the task of rapid input and output of physical move-
ments, and analog rather than digital techniques have
been used in various line rectifiers.
LR-1 FEATURES
Like other line rectifiers, the LR-1 instrument
*Bendix Research Laboratories developed the LR-1 for the Naval
Air Systems Command, United States Navy, under Contract NOw
65-0555-f.
90
produces rectified line drawings of selected images
traced on tilted photographs. The LR-1 is different
from previous line rectifiers in several respects, how-
ever. First, it is portable. The entire instrument can
be packed in two carrying cases for transportation. At
the same time, the LR-1 retains the accuracy of pre-
vious line rectifiers: known distances 3 cm or more
are rectified and plotted with a standard error of
+0.1%.
A second advantage of the LR-1 is the direct dial
entry of camera parameters and plotting scale in ap-
propriate units of degrees, inches, and amount of
enlargement. Previous line rectifiers require auxiliary
computer or slide rule calculations to make dial set-
tings.
Third, empirical rectification procedures analogous
to those used with optical rectifiers can be used with
the LR-1.
Finally, infrared line-scan records and rectilinear-
ized side-looking radar records, in addition to frame
and panoramic photographs, can be accommodated
by the LR-1.
For photographs, the focal length range is 76 to
914 mm; direct entry to the nearest 0.025 mm is
provided (in inches). The three rotation angles $, c,
and « can be entered directly to the nearest 0.01°.
The LR-1 is designed to maintain normal accuracy
from photographs tilted up to 50°, and to operate
with reduced accuracy when tilts of 50° to over 80°
are encountered. The scale of the rectified line plot-
ting can be set independently in X and Y anywhere
between one-half and ten times the scale of the equi-
valent vertical frame photograph. Principal point off-
sets up to S00 mm in x and in y can be entered.
EQUIPMENT
Figure 1 shows the LR-1 system. The output
module on the left contains the plotter unit, and the
BENDIX TECHNICAL JOURNAL SUMMER 1968
