tional content and utility. 
U.S. Forest Service 
Solution of terrain-related engineering 
problems 
The Forest Service has recognized the need 
for digital terrain models (DTM) as the backbo- 
ne of a computer-assisted terrain-related pro- 
blem-solving system. The proposition has been 
stated that the most efficient way of building a 
DTM is through the use of a digitized preci- 
sion stereoplotter, taking observations at break- 
lines of the terrain in such a way that the grade 
of a line connecting any two adjacent points 
will correspond to the grade of the terrain along 
that line. It appears that in this way the terrain 
can be defined most efficiently with the least 
number of observations. 
Most of the algorithms used for engineering 
problems relate to ground profiles between 
coordinated points. Examples include centerli- 
ne profiles and cross sections for road aline- 
ment, profiles for developing high-line logging 
systems, and selection of meandering lines with 
a uniform grade between two locations. DTM 
is used to obtain profiles in proper format for 
controlling the Zeiss GZ 1 Orthoprojector. 
An application of the DTM that promises to 
have considerable effect on future uses of pho- 
togrammetry by the Forest Services uses (1) an 
X, y digitizer, (2) DTM, (3) a general-purpose 
computer, (4) an x, y plotter, and (5) photo- 
identified ground control. The following is a 
summary of the application : 
1. An aerial photograph is resected by means 
of an x, y digitizer and photoidentified ground 
control. 
2. With the DTM, computer algorithms, 
and an x, y plotter, the x, y digitizer is made to 
simulate a stereoplotter. 
3. The output from the system consists of 
retrievable identified strings of ground coordi- 
nates. 
4. The strings of ground coordinates can be 
plotted on maps and on perspective aerial pho- 
tos, including obliques. 
This technique is expected to be particu- 
larly applicable to map revision 
State Government Agencies 
Digitized photogrammetric data 
At the Ohio Department of Transportation, 
the digitizing of photogrammetric data with 
Kelsh plotters, the Bendix Datagrid, and the 
AP /C analytical plotter is controlled by digital 
computers. The control computers either pro- 
cess the digitized data or transmit the data to a 
a large central computer. Digitizing may be 
point-by-point, time-controlled, movement- 
controlled, or a combination of these methods. 
The versatile AP/C is suitable for a variety 
of photogrammetric systems. Its current most 
economical application is in precise control ex- 
tension, computed directly in the ground-coor- 
dinate system. Other advantages include semi- 
automatic orientation ; orientation parameters 
available for setting in other plotters ; compila- 
tion at scales up to 50 times the diapositive 
scale ; valuable secondary function in automa- 
ted precision drafting; and easy adaptability 
to new applications, such as orthophotomap- 
ping and associated digital mapping. 
After a comparison study of minicomputers 
and the large IBM 1800 system, Ohio selected 
the latter. Connected to this real-time system 
are four K&E terrain digitizers and a Bendix 
Datagrid, which can be operated simulta- 
neously. Two phases remain to be carried out : 
(1) direct channel-to-channel communication 
between the AP/C and the IBM 1800 for core 
swapping and accelerated data acquisition ; and 
(2) off-line drive for the orthophotoprinter and 
the coordinatograph to free the AP/C for more 
economical work. 
Photogrammetric development of data bank 
for engineering 
The Texas Highway Department is working 
on an Automated Mapping System, which pro- 
vides an effective method for collection, stora- 
ge, manipulation, and retrieval of large volu- 
mes of map data (Howell, 1974). The system 
is designed as a modular conversion of availa- 
ble stereoplotter units to permit progressive 
conversion, which can be readily adapted to a 
total automated system. Through digitizing and 
computer programs, the imagery extracted 
from aerial photographs is filed in a data bank 
(project file) for use in multidisciplinary engi- 
neering-management applications. 
Available compilation instruments are con- 
I7