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impact, the magnitude of the effects of such an undertaking, and the surveys
and engineering work required to complete it are difficult to comprehend.
About the same time that Federal aid began, and with the rapid develop-
ment and expansion in use of aircraft, the acceptance and application of photo-
grammetry gained impetus in many fields. Concerted efforts were being made in
several countries to improve photogrammetric instruments and aerial cameras,
and to devise new techniques and procedures for solving photogrammetric prob-
lems. Photogrammetry moved into the air.
By 1921, instruments were improved to such a degree that it was possible
to compile topographic maps from aerial photographs by stereophotogrammetric
methods at scales sufficiently large for engineering purposes. In 1924, photo-
grammetric methods of compiling large scale topographic maps suitable for high-
way location became available in the United States, but were not so used. In
that year, however, aerial photographs and photographic mosaics were used in
conjunction with the location of parkways in the State of New York. About one
year later, aerial photographs were also used for highway engineering purposes
in the State of Michigan. In highway location during the next 20 years, there
was a gradual increase in the use of aerial photographs in an elemental way.
Uses included examining single photographs and photographic mosaics, stereo-
scopically examining and interpreting successive pairs of vertical photographs
of the area of survey to ascertain qualitative information governing route
determinations, and illustrating route location problems and alternatives.
Within the United States during the latter part of the 1924-19L4L period, photo-
grammetric methods of compiling topographic maps for use in reconnaissance sur-
veys to locate highway routes began to be accepted. The first compilation of
such maps for highway location purposes, however, occurred in 1930 when large
scale topographic maps were compiled photogrammetrically for locating a 60-mile
section of highway within a rugged pristine region of the State of Idaho.
For highways, the mid-1940's marked the beginning of extensive utilization
of aerial surveys, which are the actual taking of aerial photographs, and their
direct and supplemental use to obtain essential qualitative information and
quantitative data needed while accomplishing the engineering and other work.
There are three principal categories in which uses of aerial surveys for high-
ways may be classified: The first is photographic interpretation and analy-
ses; the second is graphical, instrumental, and mathematical photogrammetry;
and the third is demonstration and/or illustration. By now, such uses have
expanded into every aspect of highway engineering.
Within the United States during the forepart of 1956, electronic methods
of computation became the efficient companion of photogrammetry in highway
location and design. These methods were first used to compute alinement, pro-
file gradients, end areas, earthwork volumes, and mass diagram values, utiliz-
ing data obtained by use of both the optical train and the double projection
type photogrammetric instruments, and to compute survey traverses, solutions
to complicated design problems, and so forth. Within the past two years, ter-
rain data translators and automatic map compilation systems, employing elec-
tronic principles, became available.
The year 1953 marked the first use in the United States of electronic
methods of measuring distances for the accomplishment of basic ground control
surveys. That year the Coast and Geodetic Survey employed the Geodimeter which
was developed in Sweden and utilizes light waves. In September 1957, Califor-
nia was the first State to use the Geodimeter in control surveying for highway
location by aerial photogrammetric methods. The second electronic measuring
device, known as the Tellurometer, developed in the Union of South Africa, and
employing electromagnetic microwaves, was introduced into the United States in
March 1957. In the fall of 1957, Virginia was the first State to use the Tell-
urometer for highway project control surveying in conjunction with its aerial
surveys program. Since then, twelve other States have tested or employed this
instrument for such surveys.
