PHOTOGRAMMETRIC ENGINEERING 
a spot density of one million spots per square 
inch over an area of 9 inches by 20 inches (a 
total of 720 million bits). 
The matching program determines a mesh 
of points throughout the model which is 
sufficiently dense in every region to ade 
quately establish the terrain of that region. 
In the digital system, the scanned spots are 
grouped into rectangular blocks and assigned 
a measure of transmissivity and a measure of 
contrast. Blocks are then grouped into runs, 
subject to the restriction that all blocks in 
one run must have little contrast and must 
have similar transmissivity. A measure of 
length and transmissivity is then assigned to 
each run. A run is viewed as a feature in the 
photo, such as a field, or house. The correla 
tion technique is used to roughly identify an 
image and its conjugate by matching runs. 
Finer identification is achieved by matching 
blocks and, finally, spots. 
Automatic Image Registration 
The Itek Corporation is currently under 
taking a development program leading to a 
complete photogrammetric system auto 
mated at key-points by automatic registra 
tion techniques. In their paper, “Automatic 
Image Registration,” G. L. Hobrough and 
G. A. Wood describe an automatic registra 
tion viewer for vertical, convergent and 
panoramic stereograms. In this context 
automatic registration refers to the electronic 
sensing of image parallaxes and the automatic 
feedback adjustment of affine transforma 
tions toward registration. 
The first instrument in the proposed photo 
grammetric program, and one which is ideally 
suited to describe automatic registration in 
general, is an automatic registration elec 
tronic stereoscope known by its acronym, 
ARES. ARES differs from conventional 
stereoscopies in that the following operations 
are performed automatically by electronic 
means; F-parallax is reduced essentially to 
zero at all points in the image area; X- 
parallax is reduced at all points to values 
compatible with comfortable visual con 
vergence, and the tonal range of the ob 
served image and the sine wave response 
characteristic of the imaging system are ad 
justed. 
ARES consists of separate, closed-TV sys 
tems for the left and right stereo channels. 
The enhanced and simplified images, gen 
erated in the scanning photomultipliers, are 
presented on the viewer. The transport sys 
tem which carried the stereograms is sup 
ported on air bearings, a novel approach 
finding increasing application. 
The electronic and automation features of 
ARES consist of the scanning pattern, image 
transformation, image correlation and image 
enhancement. The scanning pattern used in 
this device is made up of crossed-diagonal 
lines and is well suited both for viewing and 
parallax sensing. In terms of image enhance 
ment only the regulation of tone range and a 
limited amount of edge enhancement have 
been included, although additional image 
enhancing features have been considered. The 
more important features are those of trans 
formation and correlation. 
To achieve the registration of two relatively 
distorted images, transformation of these 
images must occur. Hobrough and Wood de 
fine ten first and second order transforma 
tion errors. Together with X- and F-parallax, 
they represent 12 misadjustments which must 
be reduced to low values for satisfactory view 
ing. A parallax analyzer observes the video 
signals from the scanned images and detects 
differences in timing between corresponding 
detail from the stereopair. The average X- 
and F-parallaxes are removed by shifting the 
photos and the fluctuating, zero-mean, error 
signal represents a composite registration 
error signal from which the registration 
analyzer computes the corrections to perform 
the ten transformations. 
The registration of photographic images is 
certainly basic in stereophotogrammetric 
operations. The automation of image regis 
tration is an important step in the develop 
ment of a photogrammetric system to em 
ploy the wide scale variations which are 
present today. 
Omnistereomeasurer BPR 
Another versatile photogrammetric in 
strument is being developed which utilizes 
all types of photography for the compilation 
of plani metric and topographic maps. How 
ever, this instrument is primarily designed 
to aid in the solution of the problems which 
occur in the utilization of photogrammetry 
for highway engineering. Known as the 
“Omnistereomeasurer BPR” (Bureau of 
Public Roads), it is described in the paper 
“An Electronic-Photogrammetric Measuring 
and Mapping Instrument” by W. T. Pryor, 
Bureau of Public Roads, and J. H. Watson, 
Watson Electronics.