library Copy rffray Cony 

GEOLOGICAL SURVEY CIRCULAR 218 

REVISED 1958 

DEVELOPMENT OF PHOTOGRAMMETRY IN 

THE U. S. GEOLOGICAL SURVEY 

By Morris M. Thompson 
• 

•. 

-•' • - 7„. 

V f 
UNITED STATES DEPARTMENT OF THE INTERIOR 

FRED A. SEATON, Secretary 

GEOLOGIC AL SURVEY 

Thomas B. Nolan, Director 

GEOLOGICAL SURVEY CIRCULAR 218 

DEVELOPMENT OF PHOTOGRAMMETRY IN THE 

U. S. GEOLOGICAL SURVEY 

By Morris M. Thompson 

REVISED 1958 

Washington, D. C., 1952 

Free on application to the Geological Survey, Washington 25, D. C. 

CONTENTS 

Introduction 

Historical outline 

Photogrammetric instruments and 

Page 

1 

1 

Photogrammetric instruments and 

procedures developed by the 

Geological Survey--Continued 

Page 

procedures developed by the Kelsh plotter 16 

Geological Survey 3 ER-55 projector 17 

Panoramic camera 3 The twinplex 18 

Panoramic photoalidade 4 Stereodetailer 19 

Tri-lens camera 5 Portable reflecting projector . 20 

Wilson photoalidade 6 Stereotemplet triangulation . . 21 

Sketchmaster, vertical, oblique, 

and universal 7 

Orthophotoscope 

Other plotting instruments used by 

22 

Floore radial intersectors . 8 the Geological Survey 23 

Rectoblique plotter 9 Hugershoff Aerocartograph 23 

Photoangulator 10 Wild Autograph A-6 and A-8 24 

Stereoblique plotter 11 Wild Autograph A-5 25 

Topoangulator 12 Zeiss Stereoplanigraph 26 

Trimetrogon method of aerial U. S. patents issued to Geological 

photogrammetry 13 Survey photogrammetrists 25 

Mahan plotter 14 Literature cited 27 

Improvements in multiplex 

equipment 15 

ILLUSTRATIONS 

Page 

Figure 1. Panoramic camera 3 

2. Panoramic photoalidade 4 

3. Tri-lens camera in adjustable mount, bottom view 5 

4. Wilson photoalidade, original model 6 

5. Vertical sketchmaster, 1942 model 7 

6. Radial intersector assembly 8 

7. Rectoblique plotter 9 

8. Photoangulator 10 

9. Stereoblique plotter 11 

10. Topoangulator 12 

11. Model showing trimetrogon method 13 

12. Mahan plotter 14 

13. Improved multiplex equipment 15 

14. Kelsh plotter, 1951 model 16 

15. ER-55 projector 17 

16. Twinplex with ER-55 projectors 18 

17. Stereodetailer 19 

18. Portable reflecting projector 20 

19. Stereotemplet of a single stereoscopic model 21 

20. Orthophotoscope, prototype model, 1956 22 

21. Hugershoff Aerocartograph (German) 23 

22. Wild Autograph A-6 (Swiss) 24 

23. Wild Autograph A-8 (Swiss) . . 25 

24. Wild Autograph A-5 (Swiss) 25 

25. Zeiss Stereoplanigraph (German) 26 

iii 

DEVELOPMENT OF PHOTOGRAMMETRY IN THE 

U. S. GEOLOGICAL SURVEY 

INTRODUCTION 

Photogrammetry, the science or art of obtaining reliable measurements by means of photography, is now used extensively in topographic mapping. Precise photogrammetric plotting instruments 

now enable the map maker to extract from aerial photographs much.of the detailed information required for drawing the map that formerly was acquired by laborious ground surveys. Photography 

and photogrammetry have thus become essential components of all large mapping operations. 

The Geological Survey has played a leading role in the development of photogrammetric methods 

of mapping over a period of half a century. This role has been well documented in numerous articles 

appearing in technical publications during this time. It is the purpose of this circular to present, in 

brief form, the highlights of Geological Survey activities and developments in the field of photogrammetry, from pioneer efforts to present-day practice. 

HISTORICAL OUTLINE 

The Geological Survey has employed photogrammetric methods since 1904, when two of its staff 

members, C. W. Wright and his brother F. E. Wright, first used a panoramic camera for topographic 

surveys in Alaska. The first cameras used by the Wrights were improvised from commercial instruments by the addition of level bubbles and internal scales. In 1907, C. W. Wright had a camera constructed specifically for the purpose of surveying. Another member of the Geological Survey staff, 

J. W. Bagley, redesigned and improved this type of camera for use in reconnaissance mapping in 

Alaska. Bagley also designed a photoalidade to facilitate the use of the panoramic pictures in map 

making. 

In 1916-17, Bagley developed a tri-lens camera for aerial photography, and his colleague, 

F. H. Moffit, designed a transforming camera for tri-lens camera negatives. The following year, 

the Geological Survey participated with the Corps of Engineers and the Air Service in a program of 

photographing, with the tri-lens camera, several strips of country between aviation fields for the purpose of making aeronautical charts. In 1918, the Survey cooperated with the Air Service in experiments with a gyroscopically controlled camera; the resulting equipment achieved control of the camera 

axis within 2°. 

In the spring of 1920, the Geological Survey used the tri-lens camera for a systematic aerial 

survey of parts of Santo Domingo and Haiti. In the same year, the Schoolcraft, Michigan quadrangle 

was successfully mapped with the aid of single-lens aerial photographs supplied by the Army Air Service. The photographs were used for the delineation of planimetry on the field sheets; the contours 

were then added by topographers on the ground. Following the success of this project, the method was 

applied to an increasing number of other quadrangles. 

In 1921, the Section of Photographic Mapping was established in the Topographic Branch of the 

Geological Survey. In addition to the production of planimetric base maps, this Section soon turned 

part of its efforts to stereotopography. A semiautomatic stereoscopic plotting instrument, the stereoautograph, was received from Germany in 1921 and tested by the Geological Survey. This instrument 

employed terrestrial photographs only, and while workable, did not prove to be economical. A second 

instrument, the Hugershoff Aerocartograph, was imported from Germany in 1927; this was the first 

1 
automatic stereoscopic plotting instrument utilizing aerial photography to be owned by the U. S. Government. Following a number of experimental projects, the Aerocartograph was assigned to a definite 

program of complete map construction in 1930, and several good maps were produced by means of 

this instrument (Birdseye, 1940). 1 

By this time, the growing importance of photogrammetric methods had been recognized with the 

inclusion of a 40-page chapter on "Map Compilation from Aerial Photographs," by T. P. Pendleton, 

in the Topographic Instructions of the United States Geological Survey (Birdseye, 1928). The Geological Survey also published, in 1929, a report on the Alaskan Aerial Survey Expedition of 1926, in 

which it participated with other Federal agencies (Sargent and Moffit, 1929). 

When the Tennessee Valley Authority was established in 1933, one of the immediate necessities 

was map coverage of the entire valley. In cooperation with the TVA, the Geological Survey undertook 

the preparation of planimetric maps of this area, using five-lens aerial photographs and radial line 

plotting methods. The planimetric maps filled the immediate need, but there was still a long range 

need for complete topographic maps. 

Although the Aerocartograph produced satisfactory contour maps, its initial cost was high and 

it was mechanically complex. The multiplex aeroprojector effectively overcame these disadvantages, 

and in 1935 the Geological Survey purchased its first multiplex equipment. After some experimentation, the value of these instruments was satisfactorily demonstrated,and in 1936 a fully equipped multiplex mapping office was established in Chattanooga, with a program of topographic mapping of the 

entire Tennessee River Valley, in cooperation with the Tennessee Valley Authority (Pendleton, 1939). 

Beginning in 1940, improved multiplex equipment was installed in a newly established office in Arlington, Va. , and a revolutionary swing from field methods to photogrammetric methods as the basic mapmaking procedure gained full impetus. During the war years of 1941-45, the Geological Survey performed formidable strategic mapping assignments of the highest importance, using its well-established 

photogrammetric plant and personnel. Many members of its staff, called into service, played important roles in military mapping, notably Gerald FitzGerald, whose leadership in the development of 

trimetrogon mapping procedures was a contribution of the first rank (Arnold and FitzGerald, 1944). 

Following the war, the development of photogrammetric practices by the Geological Survey has 

continued at an ever-increasing pace. Each of the regional headquarters offices of the Topographic 

Division is now fully equipped so that photogrammetry plays a major part in practically all mapping 

projects. In addition to enlarged facilities for multiplex mapping, the capacity and versatility of the 

plant have been augumented by the acquisition of several universal plotters, such as the Zeiss Stereoelanigraph and Wild Autograph A-5, A-6, and A-8, as well as a considerable number of Kelsh plotters 

(developed by Harry T. Kelsh while he was member of the Geological Survey staff) . A new instrument, 

the twinplex, recently developed under the supervision of another member of the Geological Survey 

staff, Russell K. Bean, has promising potentialities. A new type of photogrammetric projector, the 

ER-55, also developed under the direction of R. K. Bean, is rapidly supplementing the multiplex as a 

basic mapping instrument. 

The Geological Survey and members of its staff have always taken a leading part in the development of photogrammetry in the United States. A continuing research program (Davey, 1949), integrated with production needs, has resulted in many improvements in equipment and procedures. Numerous articles by staff members on various phases of photogrammetry have appeared in leading 

technical journals and in a well-known surveying textbook (Whitmore, 1949) . The Geological Survey 

has contributed to the American Society of Photogrammetry four presidents (C. H. Birdseye, T. P. 

Pendleton, Gerald FitzGerald, and G. D. Whitmore), three secretaries (E. I. Schlatter, H. M. Townsend, and M. K. Linck), four winners of the Fairchild Award for outstanding contributions to photogrammetry (Gerald FitzGerald, H. T. Kelsh, R. K. Bean, and M. B. Scher), two winners of the 

Talbert Abrams Award for outstanding technical articles (W. E. Harman, Jr. and M. M. Thompson), 

1See page 27 for list of literature cited. 

2 
Figure 1. --Panoramic camera. 

3 

two honorary members (G. D. Whitmore and Gerald FitzGerald), and an editor of Photogrammetric 

Engineering (J. I. Davidson) , in addition to numerous directors and committee members. 

The Geological Survey is currently engaged in the preparation of new Topographic Instructions, 

including a comprehensive treatment of photogrammetric procedures. Some chapters of these instructions are already available. 

The Geological Survey looks forward to continuing its contributions to the science of photogrammetry through independent research, through continued cooperation with other governmental agencies 

and with private photogrammetric organizations, and through the free exchange of information with 

its colleagues abroad by way of such media as the International Society of Photogrammetry. 

PHOTOGRAMMETRIC INSTRUMENTS AND PROCEDURES DEVELOPED BY 

THE GEOLOGICAL SURVEY 

Panoramic camera 

The first panoramic camera used by the Geological Survey was constructed by C. W. Wright in 

1904 and improved in 1907 (Wright, 1908, and Bagley, 1917). The improved model was a box type in 

which the lens was revolved about a 

vertical axis by a spring, the rate of 

revolution and, in part, the exposure 

being regulated by detachable fans 

connected by gearing with the lens 

shaft. Roll film in 5- or 6-in. cartridges with several exposures each 

was placed on a circular film guide, 

so adjusted that,when the film was in 

position for exposure, all elements of 

the cylindrical surface of the film 

were perpendicular to the level plane 

and parallel to the lens shaft. The 

top of the camera, being the reference 

plane for leveling, was fitted with 

leveling-bubble slots at right angles 

to each other. Three leveling screws 

of the common type were used in connection with an adapter plate that 

fitted a plane-table tripod, thus avoiding the necessity of transporting two 

tripods. The horizontal field of view 

was 126°for each exposure, and the 

vertical range was from 18°to 22° 

above the horizon and from 26°to 30° 

below the horizon, depending on the 

width of film used. The film was 

usually developed in the field to check 

the quality of exposure and the coverage of the area to be mapped. 
In some instances, the panoramic camera was used aboard ship for the topographic mapping of 

the terrain adjacent to the shore. One such application was in the 1916 survey of Prince William 

Sound, Alaska, where the mountains rise abruptly from the water's edge. Photographs were made 

from a 40-ft launch cruising on the sound; two panoramic cameras were mounted on a stand with gimbal rings in the bow of the vessel. Prior to each exposure, the engine was shut off and the cameras 

leveled as nearly as possible. Exposures were then made at the instant the boat seemed in least 

motion. 

Panoramic photoalidade 

The panoramic photoalidade (Bagley, 1917) was developed between 1910 and 1916 for use with 

panoramic photographs taken by Bagley's parties in Alaska. Its purpose was to transfer to the map 

the information obtained from the photographs. It was so designed that the operator could sight any 

image point in the photograph and determine the horizontal direction from the station point to the image 

point, in the same manner in which the topographer operates the telescopic alidade on a plane table in 

the field. A reading glass with a vertical hair, used with a sighting vane, could be said to represent 

the lens system in a field instrument. A radial arm represented the plotting base on an alidade, and 

directional lines were plotted along this arm on the map sheet. The reading glass, sighting vane, and 

radial arm were controlled by a mechanism of the rack-and-pinion type revolving around a point representing both the optical center of the lens and the camera station. 

Figure 2. --Panoramic photoalidade. 

4 
In order to obtain differences of elevation for contour sketching, vertical aistances ul pulilLb 

'Dove or below the horizon line, which appeared as shadowgraphs on the print, were measured. A 

,imple formula that used these measured vertical distances with the corresponding map distance and 

he principal distance of the photograph gave the difference of elevation. A separate office instrument, 

mown as a rotary scale, was constructed to expedite the measurement of the vertical distance. 

Uri-lens camera 

The tri-lens camera (Anonymous, 1921) was designed in 1916-17 by J. W. Bagley, with the as-

;istance of J. B. Mertie, and F. H. Moffitt, and developed by the Corps of Engineers. It consisted 

)f a base with three compartments and a magazine capable of carrying a roll of film 400 ft long. The 

ventral compartment was equipped with an f/6. 3 lens of about 6 in. focal length whose axis pointed 

Erectly downward. The side compartments were equipped with f/6. 3 lenses of about 7 in. focal length; 

heir optical axes were inclined at 35°to the optical axis of the center lens, in opposite directions. 

The original camera was operated entirely by hand, the only automatic features being the between-theLens shutters, a pencil which marked the film at the point midway between exposures, and a dial which 

Figure 3. --Tri-lens camera in adjustable mount, bottom view. 

5 
indicated the amount of winding necessary to advance the film. The field of the camera was roughly 

three times the flight altitude. Later, cameras of this general design were built with 4- and 5-lens 

combinations. 

A transforming camera, designed by F. H. Moffitt in 1916-17, was used to project the side negatives through the angles necessary to bring the photographs to the same plane as the center photograph. 

Wilson photoalidade 

This instrument, designed by R. M. Wilson in 1932 (Wilson, 1937), and subsequently modified 

and improved, makes it possible to conduct in the office most of the operations that would be possible 

with an ordinary plane table and telescopic alidade in the field. It can be used with oblique aerial 

photographs, or with photographs taken with the panoramic camera. The instrument consists of an 

adjustable print holder, a telescope for reading horizontal and vertical angles, a centering microscope 

used to place the station point on the map sheet exactly in the vertical axis of the viewing telescope, 

and a straightedge connected with the vertical axis of the telescope so that directions from the station 

point can be plotted on the map sheet. Topographic features may be located and their altitude determined, provided oblique photographs of the same terrain have been taken from two or more different 

points of view. Thus, the sketching of contours may be controlled, just as is done by using the intersection method with a plane table. This instrument was an important factor in the success of the 

trimetrogon method of mapping. 

Figure 4. --Wilson photoalidade, original model. 

6 
ketchmaster, vertical, oblique, and universal 

This portable instrument, based on the camera lucida pririciple, was designed by I. L. Bucknaster in 1931 (Buckmaster, 1946). The vertical sketchmaster permits the transfer of detail from 

he vertical photograph to the plotting sheet, while the oblique sketchmaster is used for the same pur-

)ose with oblique photographs. The universal sketchmaster can be used with either vertical or oblique 

thotographs. By means of a mirror arrangement, the sketchmaster permits the photograph and the 

dotting sheet to be viewed simultaneously. Its adjustments are arranged to take care of scale changes 

Ind approximate tilt correction. 

Figure 5. --Vertical sketchmaster, 1942 model. 

7 
Floore radial intersectors 

In 1938, S. P. Floore developed a method of compiling a radial triangulation net in which the 

underlying map base was not covered and in which bulky or expensive templet cutters were not needed. 

In this method (Davidson and Buckmaster, 1942), slotted intersector arms made of metal are used 

instead of slotted templets. Each arm represents a radial; the radials emanating from a given point 

are bolted together to form an intersector unit. The intersector units are then assembled in a manner 

similar to conventional slotted templets. 

Figure 6. --Radial intersector assembly. 

8 
Rectoblique plotter 

This instrument was developed by J. G. Lewis, during the war years, 1941-45 (Lewis, 1945). 

The purpose of the instrument is to obtain, by mechanical means, horizontal directions of rays drawn 

from the nadir point of a set of three trimetrogon photographs to image points on the oblique photographs. The rectoblique plotter consists of a tilted table upon which are mounted two arms of different 

lengths connected by a bar free to slide parallel to the horizon. The left, or photo arm, is made of 

transparent material and is pivoted on the table at its lower end at a point corresponding to the photo 

nadir point. The right arm is known as the templet arm and pivots about a point at its lower end 

which corresponds to the ground nadir point. The templet arm generates angles in a horizontal plane 

which correspond with angles described by the photo arm in the plane of the oblique exposure. 

Figure 7. --Rectoblique plotter. 

9 
Photoangulator 

The photoangulator was developed by I. G. Lewis (1945) as an improvement on the rectoblique 

plotter. The purposes of the two instruments are identical. The basic difference between them is 

that in the photoangulator the photo arm and templet arm operate from a common pivot, whereas in 

the rectoblique plotter the two arms operate from separate pivots. 

Figure 8. --Photoangulator. 

10 
444: 4t, 4 40040, 

Stereoblique plotter 

The stereoblique plotter was developed by I. G. Lewis in 1944 (Lewis, 1945) to draw planimetry 

from overlapping oblique photographs in orthographic projection. The device is a stereoscopic plotting 

instrument containing two revolving index lines that combine in the stereoscopic model to form a vertical line piercing the ground at a definite point, the map position of which is determined by two revolving rods intersecting in a plotting pencil. The operator actuates the floating line by directly sketching 

with the pencil on the map. 

This apparatus required special treatment of the viewing stereoscope in order to reduce eyestrain resulting from the difficult perspective conditions and to meet the definite orientation requirements imposed by the oblique photographs. These conditions were met by a stereoscope, developed 

by I. L. Buckmaster, which provided the necessary adjustments. 

Figure 9. --Stereoblique plotter. 

11 
Topoangulator 

The topoangulator is a mechanical device developed by David Landen in 1944 (Landen, 1945) for 

use with trimetrogon photography, which projects photographic detail into the principal plane for elevation determination. This is accomplished by means of a transparent plate called the projector that is 

etched with a hairline. The projector and hairline are actuated by means of a slide operating parallel 

to the principal plane of the photograph. 

Figure 10. --Topoangulator. 

12 
Trimetrogon method of aerial photogrammetry 

The trimetrogon method (FitzGerald, 1944) was developed jointly, in 1941 and 1942, by the 

Geological Survey and the Army Air Forces. Important contributions to this development were made 

by the following members of the Geological Survey group: Gerald FitzGerald (who directed the group), 

I. I. Davidson, I. L. Buckmaster, R. M. Wilson, David Landen, J. G. Lewis, T. W. Ranta, J. E. 

Mundine, and Irving Gessley. In the trimetrogon method, the photography is obtained with an assembly 

of three cameras equipped with wide angle "metrogon" lenses, in which one of the cameras is vertical and the other two are 60°obliques. The technique of mapping from this type of photography involves the use of instruments already described: the rectoblique plotter or photoangulator, radial 

intersectors, the stereoblique plotter, the topoangulator, and the photoalidade. 

Figure 11. --Model showing trimetrogon method. 

13 
Mahan plotter 

This instrument (Van Camp, 1945), developed by R. 0. Mahan in 1942, is a comparatively 

simple stereoscopic mapping instrument designed to use ordinary contact prints of aerial photographs. 

It provides for plotting on a constant scale and approximate tilt correction but does not provide refinements such as correction for lens distortion. 

Figure 12. --Mahan plotter. 

14 
Improvements in multiplex equipment 

The present design of American multiplex equipment is based to a large extent on research conducted cooperatively by Bausch & Lomb and a Geological Survey group supervised first by T. P. Pendleton and later by R. K. Bean (1940). These investigations, beginning in 1938 and still in progress, 

have resulted in the construction of diapositive printers with built-in distortion correction, improved 

illumination of the multiplex projectors, improved methods of interior and exterior orientation of the 

projectors, improved tracing tables having increased range and reading directly in feet at the desired 

scale, and many other detailed improvements. 

_s'igure 13. --Improved multiplex equipment. 

15 
Kelsh plotter 

The basic principles of this instrument were conceived by II. T. Kelsh in 1943 (Kelsh, 1947), 

prior to his association with the Geological Survey, and were developed by him and other members of 

the Survey's technical staff beginning in 1947. This plotter has passed through an extremely rapid 

metamorphosis. The basic improvements over previous double projection plotters have, however, 

remained the same, namely: (1) the swinging light source, (2) correction of camera-lens distortion 

through adjustment of the projector principal distance by means of an arm-and-cam arrangement, and 

(3) contact-size diapositive plates. 

In 1951, an experimental adaptation of the Kelsh plotter was constructed by the Trimetrogon 

Section to demonstrate the possibility of its use with oblique (trimetrogon) photographs. 

Figure 14. --Kelsh plotter, 1951 model. 

16 
ER-55 projector 

The ER-55 projector, developed between 1945 and 1952 under the supervision of R. K. Bean 

(Bean, 1953), is a new kind of photogrammetric projector for stereoplotting by the direct double-projection method. The principal distinctive feature of the instrument is that the light for projecting the 

image is condensed by an unsymmetrically positioned ellipsoidal reflector instead of by a condensing 

lens system. The designation ER-55 is derived from two of the physical properties of the projector: 

ER signifies ellipsoidal reflector, and the principal distance of the projector is 55 millimeters. 

The principle of the new projector is based on a well-known property of a concave mirror conforming to a prolate ellipsoid of revolution. Light rays emanating from a light source located at one 

focus of the ellipsoid are directed by reflection toward the second focus. A diapositive plate is suitably 

positioned in the system at the appropriate principal distance from the lens. Light rays emanate from 

the light source (at one focus of the ellipsoid of revolution), pass through a red or blue filter and strike 

the ellipsoidal reflecting surface. The rays are then reflected so that they pass through first the diapositive, then the projection lens (at the second focus), and thence to the platen of a plotting table. 

From this point on, the operation is the same as that of multiplex-type instruments. A vital feature 

of the system is that no light rays pass directly from the light source to the lens through the diapositive; 

as a result, there is no hot spot caused by direct light rays, and the light distribution is relatively even. 

The chief adyantages of the ER-55 projector over multiplex-type projectors are: improved illumination of the model due to more efficient use of the available light; increased resolution in the 

stereoscopic model due to the use of a larger diapositive plate (110 x 110 mm. ); increased magnification; elimination of condenser lens; compactness; and versatility of use for either vertical or lowoblique photography. 

Figure 15. --8R-55 projector. 

17 
The twinplex 

The prototype twinplex stereoplotting instrument (Topographic Division, 1952), developed by 

R. K. Bean, was completed in 1950. It is designed to utilize low-oblique, wide-angle photography 

obtained with two synchronized and rigidly coupled cameras. The two cameras may be alined either 

along the flight line for precision mapping, or transverse to the flight line for reconnaissance mapping. 

Two unrectified diapositives, corresponding to the two exposures made at one camera station, are 

used in a set of twin projectors. Each exposure must be paired with an exposure from an adjacent 

camera station in order to produce the stereoscopic model. Once either of the twin projectors has 

been oriented in projedting position, the other projector will be correctly oriented when it in turn is 

swung into projecting position. 

Multiplex-type projectors were used on the prototype model. However, the improved model 

incorporates ER-55 projectors. The illustration shows two twin ER-55 projector assemblies arranged 

for convergent photography. The frame accommodates four twin-projector units mounted in this 

manner, or eight twin-projector units arranged for transverse photography. 

Figure 16. --Twinplex with ER-55 projectors. 

18 
3tereodetailer 

This instrument devised by E. I. Loud, Jr. , in 1951, is used in compilation review to transfer 

pertain detail from aerial photographs to multiplex manuscripts. It applies the principle of the sketchmaster to a simple lens stereoscope. The instrument can be visualized as a sketchmaster in which 

the map and photograph have exchanged positions, with a left eyepiece added so that another photograph 

zan be viewed with the left eye to give a stereoscopic image. Only one eye sees the superimposed 

image, with the effect that the lines of the map give the illusion of relief, seeming to conform to the 

relief in the photo model. No provision is made for tilt, but this is not necessary since it is intended 

to position only small areas at a time to the abundant detail of the completed manuscript. Enlargement 

ratios ranging from two times to five times can be obtained by changing the distance between the eyepiece and the large mirror, and inserting a suitable lens at the eyepiece. 

Figure 17. --Stereodetailer. 

19 
Portable reflecting projector 

The portable reflecting projector (Maltby, 1952) was developed in 1951 under the sponsorship 

of the Geological Survey. This instrument fills the need for a compact, lightweight, autofocusing projector, suitable for use in field offices for transferring details monoscopically from aerial photographs 

to a map. 

A unique feature of the projector is that it employs no counterweights, pulleys, chains, or cables. 

Operation of a single hand crank positions the lens and the copyholder automatically so that the projected image is kept in sharp focus throughout the entire range. This motion is accomplished with a 

simple but positive mechanical linkage. The hand crank is counterbalanced so that it turns easily; it 

requires less than 30 seconds to change from maximum enlargement to maximum reduction. 

General specifications of the latest model are as follows: the range of the instrument is from 1 

to 2 enlargement to 3 to 1 reduction; .any 7- by 7-inch portion of copy as large as 18 by 24 inches can 

be enlarged or reduced; over-all dimensions are 16 inches wide, 20 inches deep, and 34 inches high; 

the total weight of the instrument is 52 pounds. A carrying case is provided that takes the instrument 

completely assembled. 

Figure 18. --Portable reflecting projector. 

20 
Radial center 

on duplicate 

Templet material 

Duplicate Templet 

0 

0 

4-0 

E 

Stud 

Slot 

cg 

/2 

// Center 

I 

Stereotemplet triangulation 

The stereotemplet method for establishing supplementary horizontal control positions required 

in photogrammetric mapping procedures was devised by M. B. Scher in 1949 (Scher, 1955) . A stereotemplet is a composite slotted templet mechanically representing the horizontal plot of a stereoscopic 

optical model formed in a stereoscopic plotting instrument. (See fig. 19.) The positional data required for the preparation of the stereotemplet are stereoplotted from the geometrically faithful 

optical model. Positions of image points plotted orthographically from leveled models are rectified 

with respect to tilt and have no horizontal displacement due to relief. The function of the stereotemplet is to maintain a uniform scale relationship between any and all points plotted from a single 

model while allowing for the enlargement or the reduction of the overall scale of the templet. To 

develop control for an area covered by a number of models, the stereotemplets representing the 

various models are adjusted to the desired common scale when the templets are assembled to satisfy 

horizontal control positions. 

Air Base 

of model 

Figure 19. --Stereotemplet of a single stereoscopic model. 

21 
Orthophotoscope 

The orthophotoscope (Bean and Thompson, 1957) is an apparatus developed by R. K. Bean for 

converting perspective photographs to the equivalent of orthographic photographs. In the photographs 

produced (called "orthophotographs") image displacements due to tilt and relief are virtually eliminated so that the scale is uniform throughout the image area. The orthophotoscope must be used in 

conjunction with a double-projection anaglyphic plotting instrument, such as the ER-55 or Kelsh plotter. 

The projectors of the double-projection instrument are oriented, and the anaglyphic model is viewed, 

in the same manner for producing orthophotographs as for producing maps. 

The orthophotoscope permits continuous variation in the height of a horizontal sensitized surface. 

The sensitized surface is scanned systematically by a small slit in a screen covering the surface. The 

slit permits piecemeal exposure of the surface and also serves as a floating mark. As the scanning 

proceeds, the slit is kept "on the ground" by the observer through operation of the height-changing 

mechanism. The slit exposes each differential area to two projected images of the same object, one 

in blue-green light and one in red light; but the blue-sensitive film is not affected by the red light. 

Thus, although both the red and blue projected rays are needed to create the stereoscopic model, only 

the blue rays have an actinic effect on the film. 

When the entire model has been scanned, the film is developed by usual photographic procedures. 

From the resulting negative, enlargements or reductions can be made at the desired scale. 

Figure 20. --Orthophotoscope, prototype model, 1956. 

22 
OTHER PLOTTING INSTRUMENTS USED BY THE GEOLOGICAL SURVEY 

Hugershoff Aerocartograph 

The Aerocartograph (Hacquinius and Shuster, 1929) is a highly complex stereoplotting instrument of the optical-mechanical projection class. It is capable of producing good maps using either 

vertical or terrestrial photographs but is now considered obsolete in comparison with the more efficient Stereoplanigraph and Autographs. 

Figure 21. --Hugershoff Aerocartograph (German). 

23 
Wild Autograph A-6 and A-8 

The Autographs A-6 (Altenhofen, 1951) and A-8 are mechanical-projection type stereoplotting 

instruments of medium complexity, utilizing vertical photography. They can be used for aerial triangulation by a semianalytical method, but they are not as convenient for this purpose as the Autograph A-5 and the Stereoplanigraph, which afford continuous solutions. The accuracy of map compilation by means of the .A-6 and A-8 is of a very high order. The A-6 is operated by one man, 

whereas the Aerocartograph, A-5, A-8, and Stereoplanigraph each usually require an operator and 

an assistant. 

Figure 22. --Wild Autograph A-6 (Swiss). 

24 
Figure 23. --Wild Autograph A-8 (Swiss) . 

Wild Autograph A-5 

The Autograph A-5 (Altenhofen, 1951) is a highly complex mechanical-projection type of stereoplotting instrument, which can be used with either vertical or terrestrial photography. Both aerial 

triangulation and map compilation can be performed on the A-5 to a very high order of accuracy. The 

initial cost of the instrument is very high, but by careful planning of the special projects performed 

on it, the instrument affords long-range economies in operation. 

Figure 24. --Wild Autograph A-5 (Swiss) . 

25 
Zeiss Stereoplanigraph 

Like the Autograph A-5, the Stereoplanigraph (Altenhofen, 1951) is a highly complex and costly 

instrument, capable of performing very accurate aerial triangulation and map compilation. It is 

classified as a double-projection type of instrument, but the double projection of the conjugate images 

is viewed through a complex optical system rather than directly as in the multiplex or Kelsh plotter. 

The Stereoplanigraph accommodates vertical, terrestrial, or oblique photography. 

Figure 25. --Zeiss Stereoplanigraph (German). 

26 
U. S. PATENTS ISSUED TO GEOLOGICAL SURVEY PHOTOGRAMMETRISTS 

R. K. Bean 

No. 2,696,752, Stereoscopic photographic projection mapping instrument 

(twinplex), Dec. 14, 1954. 

No. 2,737,846, Ellipsoidal reflector projector for stereophotogrammetric 

map plotting, Mar. 13, 1956. 

App. Ser. No. 606, 788, Orthophotoscope. 

J. L. Buckmaster 

No. 2, 342, 640, 

No. 2,352,614, 

No . 2, 370, 143, 

No. 2, 670, 655, 

Optical transfer instrument, Feb. 29, 1944. 

Transfer methods and instruments. 

Camera lucida instrument and prismatic units therefor. 

Aerial photograph viewing stereoscope, Mar. 2, 1954. 

H. T. Kelsh 

No. 2,341,031, Map making and projection instrument, Oct. 12, 1948. 

No. 2,492,870, Stereoscopic projection map-making instrument, Dec. 27, 1949. 

No. 2,552,975, Photogrammetric projection machine, May 15, 1951. 

David Landen 

No. 2, 487, 814, Mapping instrument (topoangulator), Nov. 15, 1949. 

J. G. Lewis 

No. 2,321,033, Rectoblique plotter, June 8, 1943. 

No. 2,364,082, Map making from aerial photographs (photoangulator), Dec. 5, 1944. 

No. 2,561,386, Stereoblique plotter, July 24, 1951. 

R. M. Wilson 

No. 2, 261, 201, Photoalidade, Nov. 4, 1951. 

LITERATURE CITED 

Altenhofen, R. E., 1951, Accuracy and adaptability of stereoplotting instruments as revealed by U. S. 

Geological Survey practice: Photogrammetric Engineering, vol. 17, no. 3, pp. 370-375. 

Arnold, H. H. and FitzGerald, Gerald, 1944, Presentation and acceptance of the photogrammetric 

award: Photogrammetric Engineering, vol. 10, no. 1, pp. 16-19. 

Bagley, J. W., 1917, The use of the panoramic camera in topographic surveying: U. S. Geol. Survey 

Bull. 657. 

Bean, R. K., 1940, Source and correction of errors affecting multiplex mapping: Photogrammetric 

Engineering, vol. 6, no. 2, pp. 63-84. 

1953, Development of the ER-55 projector: Photogrammetric Engineering, vol. 19, 

no. 1, pp. 71-84. 

and Thompson, M. M., 1957, Use of the orthophotoscope: Photogrammetric 

Engineering, vol. 23, no. 1, pp. 170-179. 

Birdseye, C. H. , 1928, Topographic instructions of the United States Geological Survey: U. S. Geol. 

Survey Bull. 788. 

1940, Stereoscopic phototopographic mapping: Assoc. Am. Geographers Annals, 

vol. 30, no. 1, pp. 1-24. 

27 
LITERATURE CITED 

Buckmaster, J. L. , 1946, The camera lucida for aero-mapping: Photogrammetric Engineering, 

vol. 12, no. 2, pp. 235-245. 

Davey, C. H. , 1949, Current research in mapping techniques by the Geological Survey: Photogrammetric Engineering, vol. 15, no. 1, pp. 108-113. 

Davidson, J. I. and Buckmaster, J. L. , 1942, The Geological Survey radial intersector: Photogrammetric Engineering, vol. 8, no. 4, pp. 229-245. 

FitzGerald, Gerald, 1944, Reconnaissance mapping with trimetrogon photography, in Manual of 

Photogrammetry, Am. Soc. Photogrammetry, pp. 645-712. 

Hacquinius, Eric and Shuster, E. A. Jr. , 1929, Construction and operation of the Hugershoff Aerocartograph. (Manual in files of U. S. Geol. Survey. ) 

Keish, H. T. , 1947, The Kelsh plotter: Photogrammetric Engineering, vol. 13, no. 1, pp. 121-126. 

Landen, David, 1945, A principal plane photoalidade for oblique photographs: Photogrammetric 

Engineering, vol. 11, no. 3, pp. 245-254. 

Lewis, J. G. , 1945, Mechanical instruments for plotting from oblique photographs: Photogrammetric 

Engineering, vol. 11, no. 4, pp. 321-330. 

Maltby, C. S. , 1952, Portable reflecting projector: Surveying and Mapping, vol. 12, no. 1, pp. 72-74. 

Pendleton, T. P. , 1939, The multiplex stretches the survey dollar: Civil Engineering, vol. 9, no. 7, 

pp. 401-404. 

Sargent, R. H. and Moffitt, F. H. , 1929, Aerial photographic surveys in southeastern Alaska: U. S. 

Geol. Survey Bull. 797-E, pp. 143-160. 

Scher, M. B. , 1955, Stereotemplet triangulation: Photogrammetric Engineering, vol. 21, no. 5, 

pp. 655-664. 

Topographic Division, 1952, Twin low-oblique photography and the twinplex plotter: U. S. Geol. Survey Circ. 222. 

Van Camp, C. P. , 1945, Mahan plotter: Photogrammetric Engineering, vol. 11, no. 4, pp. 336-339. 

Whitmore, G. D. , 1949, Advanced surveying and mapping, Scranton, Pa. , International Textbook Co. 

Wilson, R. M. , 1937, A new photoalidade: Military Engineer, vol. 29, no. 68, pp. 434-436. 

Wright, C. W. , 1908, The panoramic camera applied to phototopographic work: Am. Inst. Min. Eng. 

Trans., vol. 38, pp. 482-497. 

Anonymous, 1921, The use of aerial photographs in topographic mapping: Comm. Photog. Surveying, 

Board Surveys and Maps, Fed. Govt., Air Service Inf. Circ. (Aviation), vol. 2, no. 184. 

28 INS. -PUP . SSC. , WASH., D.C. 36 2 3 2 
sei. 

~'.