tries and organizations probably does not fully
reflect the extent of the progress made. For
example, no reply was received from several or-
ganizations known to have made noteworthy
advances. Moreover, it was not practical to con-
tact every country, resulting in omission of so-
me significant developments.
A problem of arranging the material arose.
Information was received by country or organi-
zation, but significance can often be seen bet-
ter in side-by-side comparisons of similar appli-
cations in different organizations. We finally
decided to arrange the material by country and
organization rather than by application so that
the record of the developments at any one
source would be as complete as possible.
The bibliography lists only the literature
cited ; many valuable additional references are
available. As the literature cited includes si-
gnificant illustrations, too many to include in
this report, we decided to omit all illustrations.
Readers can obtain the originals of articles of
particular interest with the illustrations.
CANADA
Direct digitization on stereoplotting
instruments
The Topographical Survey Directorate, Sur-
veys and Mapping Branch, Department of
Energy, Mines and Resources, is developing a
computer assisted photogrammetric cartographic
system. The system will permit construction of
a digital terrain information base from data
digitized directly on photogrammetric plotting
instruments and subsequent automated produc
tion of topographic maps at various scales.
Software has been developed for the PDP
11/45 computer, which serves as a controller
and data collection unit for a number of ste-
reoplotiers equipped with simple digitizers.
The system is in operation for aerial triangula-
tion. The first phase for compilation is under-
goin production trials of collecting the data
and editing the current feature only by use of
back-tracking. Model joining and det: ailed edi-
ting will be done off-line with an interactive
system designed for editing manually digiti-
zed map sheets.
The second phase, for which the system de-
sign is now being defined, will incorporate on-
4
line interactive model joining and editing by
the stereo-operator using CRT graphics and
detailed cartographic interactive editing with a
CRT graphic us tablets, and possibly di-
gitizing table.
Automatic production of contours
and orthophotos
A highly significant Canadian development
is the Gestalt Photo Mapper II, which produ-
ces automatic contouring in addition to ortho-
photos (Crawley, 1974).
To produce orthophotos at the scale of acrial
photographs, the Gestalt Photo Mapper II dif-
ferentially rectifies homologously scanned areas
(9-45 x 8-55 mm at photoscale) and uses the
parallax signals so generated to produce con-
tcurs simultaneously. The orthophoto and con-
touring process occurs in real time under the
control] of a 16k minicomputer programed in
assembler language. The space model is simu-
lated by the computer according to the para-
meters of relative and absolute orientation. Phi,
omega, kappa, and scaling are effected by elec-
tronic raster shaping according to the orienta-
tions.
Contouring occurs as follows: A matrix of
height values, 52x 47, makes up the transfor-
mation map for the 9.45x 8.55 mm scanning
window. The correlator calculates an average
value for every 180x180 tm subarea of the
scanning window. For contouring, the diffe-
rence between each matrix value and its neigh-
bour is interpolated into 8 equal increments in
y and 4 in x to form a straight line to the 4
ad’oining neighbours. Contouring is done in
real time with digital electronics by intensi-
fying the printing CRT beam at the points of
intersection of the contour planes with the in-
terpolated height matrix. All the intersection
points are printed in one 20 ms scan of the
9X8 mm patch area.
In adition to the orthophoto and contouring
outputs of the GPM II, a sparse Digital Ter-
rain Model is printed with the contour sheet.
D'TM's of any grid density, to 180x 180 pm,
can be recorded on paper or magnetic tape. At
a grid density of 180 x 180 jum (photoscale),
slightly less than one million height values
could be recorded for the stereo overlap area of
near-vertical photographs.
The programable nature of GPM II promi-
