pid generation of contours from ideal stereo-
pairs of laboratory close-range objects (Wer-
theimer and Givens, 1974). One, the positive-
negative system, can use either coherent or in-
coherent light and produces dark contours on
a structure-filled background. 'The second, the
scatter-plate system, produces bright contour
bands on a dark field. As usual with optical sys-
tems, for a given x separation all contours are
displayed simultaneously.
Itek Company reports the development of
spatial signatures by analysis of the Fraunhofer
diffraction patterns of selected ERTS (LAND-
SAT) images (Corbett, 1973). These signatures
are used to classify mountainous, urban, and
cultivated areas. A special Fourier plane filter
was developed to suppress noise in the diffrac-
tion pattern; the filter is a mask made as a
transparency of the diffraction pattern of an
image area (from LANDSAT) with no detail,
such as water.
Automated design of sewer networks
A joint project of the Brooklyn Polytechnic
Institute and the firm of Lockwood, Kessler &
Bartlett developed a system for automating de-
sign of sanitary-sewer networks (Soehngen, De-
Cicco, and Baker, 1873). The system uses spe-
cial terrain information from 2-axis digitized
orthophotos and g-axis digitized photogramme-
tric models. The information for construction
of the data bank includes nodal points for street
intersections, additional nodal points to define
street curvature, street profiles, locations and
elevations of houses on both sides of the street,
sidewalk and curb locations, and locations of
manholes and catch-basins. Data digitized from
orthophotomaps are transformed to the State
plane coordinate system by a 4-parameter trans-
formation. Time for digitizing from orthopho-
tos is about go minutes for a 2,000-ft stretch of
street. For 3-axis digitizing, an A8 with H. Dell
Foster readout on cards is used. For economy
it is advantageous to digitize the model at the
same time the topographic map is produced.
CONCLUSIONS
This review of ongoing developments in the
automation of photogrammetry may be confu-
sing to the reader because there are so many
different aspects of the subject and because ad-
vances are being made in so many different di-
rections. Moreover, this review deals with only
a fraction of the total effort and can be const
dered only as representative of the kinds of pro-
gress being made.
Nevertheless, some distinct trends be
summarized as follows :
can
1. The practice of equipping available ste-
reoplotting equipment with simple digitizers
is widespread. Such systems entail a relatively
modest investment and permit compilation of
a digital terrain data base from data digitized
directly on the stereoplotting instruments.
2. There is a growing tendency to use mini-
computers on-line with available stereoplot-
ters, with several plotters connected to one
computer.
3. Production of digital terrain models from
stereomodels can be optimized by using pro-
gressive sampling, in which the local density of
the point grid is matched with terrain rough-
ness.
4. Techniques of density correlation on epi-
polar lines offer a promising means for econo-
mical digitization of a photogrammetric model.
5. Systems based on sophisticated instru-
ments, such as analytical plotters, UNAMACE.
and Gestalt Photo Mapper II, permit simulta-
neous automatic production of orthophotos,
contours, and a digital terrain model. These
are available, but the large capital investment
is beyond the economic reach of small organiza-
tions.
6. Off-line orthophoto systems, in which the
orthophotos are generated by differential recti-
fication separately from height-control data, of-
fer a potential economical means of orthophoto
production.
7. In a new approach to representation of
data obtained from a photogrammetric model,
the computer transforms the data into an ener-
gy spectrum, and light pulses fed from the com-
puter generate a digital relief model.
8. Techniques of digital image processing
have progressed to the point of having many
practical uses such as modification of intensity
and geometry, enhancement of detail, and
change detection. An important potential ap-
plication is in map revision. (The Oct. 1974
issue of Photogrammetric Engineering was de-
voted entirely to automated imagery proces-
sing.)
