Metrical Photography*

Metrical Photography*

GOMER T. MCNEIL, President, Photogrammetry, Inc., Silver Spring, Maryland

ABSTRACT: Metrical photography is defined as the art and science of obtaining reliable measurements by means of photography. The accepted scientific word, having the same meaning as metrical photography, is photogrammetry. A summary of the highlight material presented is: brief history of the heritage of the perspective from the primitive age to the advent of the camera, the perspective from the viewpoint of the artist and the engineer, the father of photogrammetry, the camera as an angle recording instru­ ment, integrating the knowledge, practical experience, and instrumenta­ tion of the technical photographer and the photogrammetrist for the purpose of serving science, engineering, and industry by means of photo­ graphic measurements.

INTRODUCTION clslOn, one major component cannot be TJ 7 HA T is metrical photography? The considered more important than another if rr word "metrical" is an adjective one honors the adage that the chain is no meaning "measured." The word "pho­ stronger than its weakest link. Neverthe­ tography" is derived from the Greek, less, the theoretical heart of the photo­ meaning "to draw with light." It may be grammetric system is the photograph or concluded from the word derivations that perspective drawing. Data recording and metrical photography has something to do data reduction instrumentation perform with measuring a drawing that was pro­ their primary function of reconstructing duced by the action of light. object space in accordance with the theory The accepted scientific word, having the of perspective. same meaning as metrical photography, is photogrammetry. "Photogram" meaning PERSPECTIVE DRAWING "photograph" and "metry" meaning If the perspective drawing is, figura­ "measurement." Therefore, photogram­ tively, the center of the photogrammetric metry is the science of photographic meas­ universe, a brief review of its heritage may urement. prove beneficial in that current or future The artist or engineer may think of the solutions to problems can be more fully ap­ photograph as a perspective projection or preciated, conceived, and exploited. drawing that illustrates the basic facts of The word "perspective" is also derived shadow and perspective. The artist and from the Greek, meaning "to see across." engineer have more points in common than Realism is given to a painting by aerial and is normally realized, but if we must dis­ linear perspective. Aerial perspective is the tinguish between them perhaps the sim­ haze effect given to distant objects, and plest terms of distinction are that the artist linear perspective is the geometric con­ deals with the intangibles of beauty while figuration resulting from projecting object the engineer deals with the measurable. space through a perspective center onto an In an integrated system of balanced pre- image surface. * From a paper presented before the Fifth National Industrial Photographic Conference and reprinted with permission from The National Photographer, the official publication of the Photog­ raphers' Association of America, Inc. EDITOR'S NOTE: The author presented this paper at two meetings during March 1957. The first was at a regular meeting of the Engineering Society of Cincinnati and the other at the Fifth Annual Industrial Photographic Conference. These and the published paper constitute one more outstanding demonstration of the efforts made by Society Members to "sell photogrammetry" to non-users who would benefit through use and to others who now know little or nothing about this relatively new science. 667 668 PHOTOGRAMMETRIC ENGINEERING

Primitive art lacks perspective, but sometimes there is an apparent awareness.2 Ancient Chinese art portrays aerial per­ spective but not linear perspective. Fore­ shortening is evident on painted Grecian vases dating back to 530 B. C. The per­ spective, however, did not rigorously con­ form to geometric projection. The Romans inherited perspective from the Greeks. Since the Romans were interested in real­ istic paintings and statues, they sought to display perspective accurately. As Roman power increased and the Christian era took FIG. 1 hold, realism in art declined in favor of art expressing spiritual values and symbols of faith. Realism in art was so infrequent in the centuries to follow that by the time of the Renaissance, perspective was re-estab­ lished as though it were a new discovery.

THE RENAISSANCE-REDISCOVERY The Renaissance has been defined as the ~- rediscovery of man, nature, and classical . antiquity. I prefer to call it the rediscovery of perspective. Artists turned again to real­ ism and by the sixteenth century the prin­ POINT PERSPECTIVEI ciples of scientific perspective were ac­ FIG. 2 cepted as a part of the revival of realism. Artists and geometricians examined the principles of scientific perspective to clarify and discover geometric and mathematical relationships. Art and science came upon the law of inverse squares: If an object is moved to twice its distance, the image is reduced to one-fourth of the original area. ~ Artists of the Renaissance enthusiastically .[,;::::----1" experimented with the new science of per­ spective. Leonardo da Vinci was closely allied with the development of scientific perspective. His world famous painting, 2 "The Last Supper", (Figure 1) is an excel­ ~POINT PERSPECTIVE lent example of parallel or one-point per­ FIG. 3 spective (Figure 2). The lines formed by the panels on the ceiling, the window frames, the edge of the table, and the dec­ orations on the side walls, all represent a system of parallel lines in object space. These construction lines on the painting converge and intersect within the image of the head of Jesus. Artists of the Renais­ sance occasionally presented angular or two-point perspective (Figure 3) and oblique or three-point perspective (Figure 4). The significant difference between the practical utilization of the perspective by the artist and the engineer is the degree of geometric fidelity. If the accuracy of the FIG. 4 METRICAL PHOTOGRAPHY 669

linear perspective is not faithfully repro­ ver. However, with the advent of the duced, the intangibles of beauty in the camera, realistic presentation as a means mind of the artist or observer may not be to instruct was no longer regarded as a compromised in the slightest, but even aug­ primary function of art. Abstraction and mented. However, if the eI)gineer's task is surrealism evolved as two new forms of art to reproduce the scene, the error in the to counteract the competition of the linear perspective may result in measure­ camera that served so effectively in pre­ ment data that are unreliable for the suc­ senting realism for instructional purposes, cessful execution of the project. The artist can legitimately throw linear perspective METRICAL PHOTOGRAPHY HISTORY to the winds under the law of artistic It is not uncommon to hear metrical license while the engineer must determine photography referred to as a budding new if the residual errors of the perspective are science without realization that the science compatible with the accuracy specifica­ of photogrammetry is over 100 years old. tions of the project. The principle that a photograph is a The contribution of Brook Taylor to the perspective projection of mathematical field of mathematics is well known by accuracy was recognized by Arago and mathematicians throughout the world but Guy Lussac4 in 1839. his contribution to the mathematics of the Aime Laussedat, an officer in the French perspective is little known. In 1920, J. W Corps of Engineers, is known as the father Gordon noticed an announcement that a of the applied science of photogrammetry. portrait of Brook Taylor had been' added In 1852, the same year as the founding of to the National Portrait Gallery in Trafal­ the American Society of Civil Engineers, gar Square. To pay his reverence to this Captain Laussedat made a photographic great English mathematician, Gordon survey of a small village near Paris at the made a' pilgrimage to the Gallery. Much to invitation of the French General Staff. 9 Gordon's surprise he did not find a por­ Eight collodian wet plates were exposed in trait of Brook Taylor but a miniature three hours. A topographic map at a scale study in perspective. The fact that Taylor of 1:2,000 covering 500 acres was prepared was represented by a study in perspective from the photographs in four days intrigued Gordon inasmuch as he was cur­ Laussedat claimed that the success of rently in the process of preparing a manu­ his method was due to determining the pre­ script entitled "Generalised Linear Per­ cise focal-length of the camera lens, and spective."3 This resulted in a second pil­ recording the principal point and horizon grimage, this time to Bloomsbury in quest line on each horizontally exposed photo­ of Taylor's book. Gordon writes of his ex­ graph. perience: "Then came one of the moments In 1864, while an instructor at the School for which the student bibliophile lives, of Arts and Crafts in Paris, Laussedat an­ when in the neglected page of an old author nounced a course in photographic survey­ he discovers unsuspected treasure. Here, ing for rapid reconnaissance and for exten­ in Taylor's twenty-fifth proposition, al­ sion of the photographic method to the most at the end of a slender volume, was surveys of buildings and machinery. the rule for finding the horizon in a perspec­ Laussedat corresponded with scientists tive field, whether erect or oblique, which throughout the world, promulgating the bridges the gap between a photograph and new science internationally. His work was a plan of the photographed country. In not lost, then, when a stubborn resistance 1715, when that page was printed, no pho­ to photogrammetry developed in the tograph had ever been taken, no practical French Army. application of the rule could be foreseen. It Although Laussedat is universally recog­ was pure unapplied science, wrought, as nized as the father of photogrammetry, the devotees of knowledge work their ma­ others were independently working with terial, to the roundness of a systematic the problems of photographic surveying, whole." for example, Porro in 1853 and Meyden­ Until the middle of the nineteenth cen­ bauer in 1858. Bertaud in 1858 produced a tury, artists were concerned with repre­ lens with a 30 degree field and Brunner in senting the natural or supernatural in 1859 utilized Bertaud's lens in the first terms of the natural. The painting served serviceable camera for photographic sur­ to instruct as well as to please the obser- veying. 670 PHOTOGRAMMETRIC ENGINEERING

Inasmuch as photographic surveying "Wind, Sand and Stars." "The machine it­ was recognized internationally by military self retreats behind its functions as it be­ authorities as a means of preparing maps comes more perfect. I t seems that every for defense, the promotion of photogram­ technical attack of the human being, all metry began in many lands. computations, all night vigils over plans and drawings, ever and again produce, as BEAUTY OR GEOMETRY final visible result, the greatest simplicity. The development of photogrammetry for Obviously perfection does not arise when the past 100 years would, indeed, make an there is nothing further to be added, but interesting technical saga of the integration rather when nothing further can be taken of men, optics, mechanics, engineering, away. In its highest perfection the machine economics, and specialty salesmanship. becomes inconspicuous. Perfection of an Such a history would require more time invention borders closely on absence of in­ that is allocated to me here. The purpose of vention. Only when every visible trace of presenting the short history of the perspec­ technical elaboration has disappeared from tive from the primitive age to the time of our instruments and we see them as self­ Laussedat is to emphasize and give mean­ evidently and naturally as gravel rounded ing to the difference between a photograph by the sea, will one gradually forget that it as a picture of beauty and the photograph at all is a matter of a machine." as a drawing conforming to geometric and Photogrammetry, or metrical photog­ mathematical relationships. The signifi­ raphy, has many uses. The popular concep­ cant point is to know the difference and tion of photogrammetry is confined to plan the photography accordingly. mapping, and with good reason. For both We are basicatly interested in the utili­ economic and military reasons, the map­ tarian role of physics, chemistry, and ping of the face of mother earth has been mathematics as they team up with engi­ the most significant single applic'ation of neering to solve practical problems. Almost photogrammetry since its founding by everyone is elated at the sound of the word Laussedat. Photogrammetry is, and has "practical." Even in those rare moments been,primarily preoccupied with theory when man is struck with a bolt of true hu­ and instrumentation for the specialized mility, he seldom confides that he is not application of mapping the irregular sur­ practical. We must not discount the fact face of the earth to fulfill an ever-increasing that the abstract theories and the so-called need for maps. The photogrammetrist has long-haired mathematical equations of to­ specialized and has become expert, in the day are potentially the framework for the past 100 years, in the determination of solution of the practical problems of tomor­ space positions. row.

OBSERVATION AND MATHEMATICS PHOTOGRAMMETRY COVERS BROAD FIELD As we all are very much aware, knowl­ There is more to photogrammetry than edge in all physical sciences is based on mapping, however. Photogrammetry is observation,u Observation, however, can officially defined by the American Society determine only what is. When observation of Photogrammetry as "The art or science is combined with mathematics it is possible of obtaining reliable measurements by to predict what can be. means of photography." It should be par­ Once a workable theory is established in ticularly noted that the photography is not metrical photography, instrumentation is confined to an aerial exposure station fbr required to record and to reduce the data. the purpose of topographic mapping.s The The continuing requirement for increased metrical photography may be exposed from aC<;.l,lxacy of data recording and speed of the air, ground, underground, water, under­ data reduction poses development consid­ water, or within the confines of a building erations of time and finances. However, for the purposes of topographic mapping, man, time, and finances do eventually astronomy, ballistics, architecture, medi­ simplify instrumentation. For the past 50 cine, anthropology, zoology, physics, biol­ years photogrammetry, like many other ogy, geology, meterology, hydrography, sciences, has been dominated by machines. deformations, criminalistics, industrial A stimulating thought about machines ap­ measurements, physical education, avia­ pears in Antoine de Saint-Exupery's book1o tion, military intelligence, or determining METRICAL PHOTOGRAPHY 671 the dimensions of an individual for a tailor­ the methods, techniques, and instrumenta­ made suit. Metrical photography is capable tion that are compatible with accuracy, of determining the position of points, the cost, and operational requirements. orientation and length of lines, the area of The significant advantages of metrical surfaces, and the volume of solids. photography are: Metrical photography can also be used 1. REMOTE CAMERA STATION (FIGURE 5) to determine time, and quantities inte­ Measurements can be made without grated with time, such as velocity and ac­ touching the object or occupying the celeration. Time may be recorded on the immediate vicinity of the object, for exposure, or the exposure sequence may be example, in radioactive, explosive, gase­ time-controlled by electromechanical com­ ous, hostile, inaccessible, and security ponents. When the space positions of two areas. Minimum mental and physical points are known, the distance between the demands are important to the operator points can be determined. Distance rela­ working under adverse weather condi­ tive to time is velocity. The time rate of tions or in dangerous areas. Data can be change of velocity is acceleration. Time reduced under favorable office condi­ can be solved for by the photogrammetrist tions and at a convenient time. The because the solution is dependent on a remote camera station is of obvious ad­ direct measurement in image space. vantage to the military, but it has now The key to the capabilities of metrical been extended to business in those cases photography is that a direct measurement when management does not wish to dis­ in image space can be used to determine an play overtly their initial interest or indirect measurement in object space. plans of a proposed development to the In the field of science, whenever indirect public or competitors. measurements are determined from direct 2. FREEZE PHENOMENA IN MOTION measurements, one must traverse the inter­ (FIGURE 6) connecting link of theory. The intercon­ A point object in motion can be stopped necting link in the science of metrical and measurement data obtained. In de­ photography is the theory of perspective. formation problems where many points The theory is proven when all indirect may move at varying rates, the action measurements based on it are verified. of the many points can be frozen simul­ While the photogrammetrist has been taneously and the deformation relative primarily absorbed with the problems of to time determined without the influ­ interior orientation, exterior orientation, ence of friction or inertia, since the point and the calibration of the opticomechanical objects have no mass but position only. instrumentation, scientists, engineers, 3. PHOTOGRAPH SERVES AS AN ELABORATE chemists, and technicians have been busy SURVEYOR'S NOTEBOOK (FIGURE 7) in other photographic societies with the Photographs can be stored as a perma­ problems of film, filters, optics, processes, nent record and made available for lighting, cycling rates, and instruments and checking, and if required, additional apparatus of many functions. data reduced at a later date owing to It is apparent that the future growth of the wealth of detailed points. metrical photography into the many 4. ECONOMICAL (FIGURE 8) branches of science, engineering, and in­ Metrical photography is basically eco­ dustry is as optimistic as a seed catalog. nomical through the saving of time and The photographer and photogrammetrist therefore money. However. in certain have already established the necessary instances time may be considered more ground work. First, science, engineering, important than economy. and industry must be informed that 5. RELIABILITY (FIGURE 9) metrical photography is a proven scientific This is one of the basic reasons for pho­ method of measurement, and what metri­ tography's high regard in military cir­ cal photography can and cannot measure cles. Ground intelligence reports may with sufficient accuracy and economy. Sec­ indicate, for example, a possible oil stor­ ond, the photogrammetrist and the scien­ age capacity of 1,000,000 barrels. A high tist, engineer, or industrialist must deter­ degree of reliability is established when mine what the requirement really is and the data can be measured from photo­ mutually state the problem. Third, the graphs instead of relayed in words that photogrammetrist must make available cannot be verified. 672 PHOTOGRAMMETRIC ENGINEERING

r

1-I REMOTE_ _CAMERA STATION-'

FIG. 5

FREEZE

PHI.NOMENA FIG. 9

Basically, a metrical camera is an angle­ recording instrument similar in function to a transit. The metrical camera, however, simultaneously records many pointings to objects while the transit is confined to one pointing at a time which is represented by the intersection of the cross-hairs. FIG. 6 Let us review a very simplified case of transit surveying6 (Figure 10): a. The base line AB is measured. As­ P~o+osrap" serves as sume AB is horizontal. elaborate surve .or's b. A transit is positioned at A and the angle a is recorded. . c. The transit is moved to B and the angle b is recorded. d. The angle (J is equal to 1800 -(a+b). e. From the law of sines the distance from each of the base terminals to the object point P can be determined: AB AP=-.- (sin b) sm () FIG. 7 AB BP=-.- (sin a) sm () It may be summarized then that any point in object space can be positioned horizontal1y, if a horizontal base length and the included horizontal basal angles to the point are given. Let us also review a very simplified case of photographic surveying (Figure 11): a. Two metrical cameras are geometri­ cally arranged so that their optical axes are horizontal, paral1el to each other, and perpendicular to the cam­ era base which is also horizontal. This FIG. 8 is called the normal case of stereo- METRICAL PHOTOGRAPHY 673

TRANSIT transit. In practice, however, the mathe­ matical reduction of the three-dimensional SURVEYING position of an object point, under the nor­ mal case of stereo-photogrammetry, would be performed as follows (Figure 12): a. Measure the photographic coordi­ nates x, and Z, on photo 1 and Xz and zz on photo 2. b/ b. The camera base, B, and the focal I length, j, are measured or are known BASE LINE from being previously calibrated. B c. The constant, K, is determined: FIG. 10 B K=-- XI-XZ

photogrammetry. d. The X, Y, and Z coordinates of the b. The angle subtended at the lens A object point are simply determined between the optical axis and the by multiplying K by X" j, and z" image of Pis: respectively. tan c=rnlj Inasmuch as the procedure can be uti­ also at lens B: lized to determine the three-dimensional tan d=nlf. position of more than one point, the abso­ c. Angle a=900 -c lute distance from one object to the other or Angle b=900 -d 0 0 0 d. Angle = 180 - (90 -c) - (90 - d) =K~ e X =Kx1 y =c+d where e. The base AB, or the distance between the twin lenses, is measured. f. The base and the two included basal angles are now determined. It is then possible to employ the same proce­ dure to position the point P as was previously outlined for the transit surveying procedure. The vertical position of the object point is simply determined by multiplying the horizontal distance from the camera sta­ FIG. 12 tion to the object by the tangent of the angle of elevation or depression. These mathematical relationships dem­ the siz., of objects can be determined with­ onstrate that the metrical camera is an out knowing or measuring a single dimen­ angle-recording instrument similar to the sion in object space. All that one needs to know is the calibration data of the camera. It is believed that this unique condition should be of great interest to the field of Pltotosraphic. science, engineering, and industry. There Surveyins p are no metrical requirements placed on the e photographer such as taping distances, or • placing the customary pack of cigarettes : or ruler in the field of view for the purpose ..;;: c: of an approximate scale. If the purpose of ..: ".c: the project is to determine the position of L~ objects without reference to a horizontal o· , : a plane, the camera base and optical axes A . ...l...- -ij need not be held horizontal, and the ex­ CANPA BASE posures may be made from any angular rr== orientation. The stereo camera is calibrated FIG. 11 by the photogrammetrist before it is taken 674 PHOTOGRAMMETRIC ENGINEERING to the field of operation and the film is 4! inch centers and two valves between the metrically reduced by the photogram­ windows and the furnace. metrist subsequent to the exposures. The The valves were closed whenever it be­ only stipulation placed on the photogra­ came necessary to remove the windows for pher is the most effective technical com­ cleaning without cutting off the furnace. position. A fully reflecting beam-splitter for the motion-picture camera was constructed PHOTOGRAMMETRIC EVALUATION AT WORK and consisted of two outer mirrors with A few applications of metrical photog­ screw adjustments for convergence and inne~ raphy will now be presented. They are not two mirrors, the latter being formed by aluminizing a right-angle prism. necessarily the most interesting, im­ portant, glamorous, frequently encoun­ The beam-splitter is placed about 12 tered, nor are they necessarily representa­ inches from the camera lens. The 16 mm tive of the many thousands of applica­ motion-picture frame (Figure 15) is split tions that will materialize someday. It is vertically with images from the left and hoped that these run-of-the-mill examples right mirrors of the beam-splitter. will function as a lever to the imagination. A single-lens motion-picture camera with An excellent demonstration of resource­ a split frame records the left and right fulness is illustrated by Charles Burnsl of images simultaneously and thereby pre­ the British Iron and Steel Research Asso­ cludes the problems of synchronization and ciation (Figure 13). The association was more elaborate instrumentation. confronted with the problem of securing The standard Bolex stereoscopic pro­ information "on the 'combustion zone' of jection lens with built-in polarizing filters the blast furnace where the pieces of iron is mounted on a standard projector, and ore, coke and limestone, which fill the with the aid of polarized glasses the slow­ furnace, are burned together to produce motion pictures or the single still frames iron under a blast of preheated air." The are viewed on the screen in 3-D. The still furnace reaches a temperature of 1,900°C. frames are used to determine the meas­ and is separated from the observer by a urement data of the particles in motion. wall of refractory brick several feet thick. A very simple measuring device, or an­ The preheated air is forced into the alyzer (Figure 16), was easily, rapidly, and furnace through a tuyere which is approxi­ cheaply constructed from war surplus mately 8 feet long and 8 inches in diameter. equipment. Mirrors with the necessary One end of the tuyere contains a door with movements were obtained from an aerial a small inspection window through which sextant and the spotlights from gunsight the violent motion of the particles can be collimators. viewed under the influence of the blast of The analyzer works like this: Two light the preheated air. beams are adjusted so that one beam falls The potentially significant measure­ on the left image and the other beam falls ments for design consideration of blast on the right image of the particle on the furnaces are the depth of blast penetra­ screen. This condition is accomplished tion and the distance over which the parti­ stereoscopically. The stereoscopic probe­ cle motion occurs. beam is adjusted so that it falls on and ap­ It was found that motion pictures at a pears to float at the same depth as the rate of 64 frames per second were blurred stereoscopic image of the particle. The beyond recognition. However, a rate of stereoscopic probe-beam is so coupled to a 1,000 to 3,000 frames per second resulted mirror system that two converging plot­ in well-defined single frames and a slow­ ting-beams are projected to the side of the motion picture at normal projection instrument at the same scale as object speed. The intense illumination from the space. The known distance to, and the furnace permitted the lens to be stopped diameter of, the tuyere nose are used as down to a relatively small aperture. control data to adjust the analyzer. A full­ The tuyere door was modified (Figure scale plot is compiled of all the particles in 14) to accommodate stereoscopic motion­ the stereoscopic field of view and velocities picture photography by the insertion of computed. A reasonable estimate is also two circular windows of fuzed quartz on made of the nature of the cavity created METRICAL PHOTOGRAPHY 675

FIG. 13 FIG. 15 by the blast in the region not covered Brief outlines of some medical problems stereoscopically. involving three-dimensional space meas­ The solution of this unusual problem in urements are;s stereoscopic cinephotography is an intrigu­ (a) Deformation and swelling. ing demonstration of conforming to the (b) Correlation of specific diseases with performance specifications and still main­ particular body types, surface area, taining simplicity based on ingenuity and and volumes. It is of interest to resourcefulness. point out that the method to deter­ Metrical photography is not used to any mine the body area is to paste small significant degree in the field of medicine. pieces of paper over the patient and Still, motion picture, and stereoscopic to measure the total area of the photography are frequently utilized in paper. medicine but basically for qualitative and (c) Tumorous growth of the eye. The not quantitative analyses. Dr. E. A. Mis­ rate of growth of the tumor is some­ kins ventures to state "That little use of times the deciding factor as to measurement of stereoscopic photographs whether the eye should be removed. is made is perhaps due to the medical prac­ (d) Location of opaque objects in the titioner's usual dislike of anything mathe­ body. Stereo X-ray negatives have matical; particularly is this the case when been used for many years but little errors of precise measurements are con­ use has been made of measurements. cerned. Stereoscopy as a means of illustra­ tion is used much more widely and there is Another use of metrical photography is no doubt that the technical skill and adap­ better appreciated in Switzerland than the tability of the medical photographer is United States. For many years the Swiss high, both in the field of black and white, Police have been covering accidents with and in colour photography. The ability to stereometric cameras. The Swiss law en­ produce good stereo-pairs is not lacking, forcement authorities are to be congratu­ and the possibilities of this type of photog­ lated for their foresightedness and techni­ raphy are appreciated." cal approach to accident evaluation. Un-

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FIG. 14 FIG. 16 676 PHOTOGRAMMETRIC ENGINEERING

iortunately, no such comprehensive techni­ aircraft at the time of engine failure. The cal approach to accident evaluation is evi­ flying height would tie in many loose ends dent in this country. We have always been of other scientifically prepared data. The under the impression that as soon as an testimony of witnesses as to this height economic need existed for a particular varied from 200 feet to 2,000 feet. Very commodity or technique that it would little progress was being made with the case soon be developed and distributed. I t cer­ until nearly two years subsequent to the tainly appears to us that something equiva­ accident when the lawyer learned that lent to the Swiss approach to accident movies were being exposed at the time of evaluation is timely for application in this engine failure. The lawyer was an ex­ country. For example, during the past dec­ Marine officer with experience in the Pa­ ade the City of New York has had over cific Theater, and was generally familiar 1,000,000 automobile accidents resulting with the role aerial photography played in in more than 6,000 deaths and 500,000 in­ the successful execution of the war. He rea­ juries. During the past years the premiums soned that possibly an altitude could be on automobile insurance have increased determined from the color transparency appreciably throughout the country, ow­ by a specie of the human race technically ing to an increase in the number of acci­ referred to as a photogrammetrist. dents, much larger judgments awarded by The problem was as challenging as it was juries in law suits, and substantial in­ novel. First, the 8 mm. movie-camera was creased costs of automobile repairs. calibrated for focal-length and plate per­ Even though the police authorities may pendicular by an application of a technique conclude that capitalization of stereometric well-known to surveyors as the three-point accident apparatus may not be financially problem. Two days were spent over the feasible at this time, it may prove eco­ microscope examining one frame of the nomically sound for the various automo­ color film to identify control points. Six bile insurance companies to mutually sup­ control points were selected for two inde­ port such a program. Favorable decisions pendent solutions. Distances between the to only a few large litigations would more control points averaged approximately than cover the initial investment. Our one-tenth of an inch. The corresponding company served as photogrammetric con­ ground-control points in the vicinity of the sultants on an accident case that involved crash were surveyed. The flying height, suits amounting to more than a quarter of tilt, and swing were determined by a graph­ a million dollars. The awards resulting ical method. 7 The computed values re­ from four such cases would procure a mil­ sulted in an altitude of 700 feet and a tilt lion dollars worth of stereometric equip­ of 40 degrees. ment. 'vVe are of the opinion that the eco­ I nasmuch as the flying height was nomic need is apparent. Possibly the par­ greater than 500 feet, thereby conforming ties that would have most utilization of the with aeronautical regulations for the photogrammetric procedure are not cog­ countryside, it was the first big turning nizant of its presence or availability. point in the status of the case. The flying An interesting example of photogram­ height was then integrated with other metric evaluation was experienced a few complicated tech nical data, and the evi­ years ago. A lawyer presented me with an dence took firm shape for the first time. inexpensive 8 mm movie-camera and a roll The case was soon settled out of court, al­ of colored film poorly exposed on a hazy though it was three years subsequent to day. The lawyer requested that I deter­ the aircraft accident. The lawyer grate­ mine the altitude of the aircraft when the fully acknowledged that the successful con­ last frame was exposed. The plane had been clusion of the case was due largely to the occupied by the pilot and a passenger. The metrical data made available through pho­ passenger was exposing low-oblique aerial togrammetry. movies of the countryside. The aircraft en­ After the file covering the accident was gine suddenly stalled. The passenger stamped "Closed" and neatly filed away, I stopped taking movies, the plane crashed, visited the lawyer to learn to what degree the pilot was killed, and the passenger the science of photogrammetry had im­ severely injured. The case had many legal pressed him. The lawyer offered four sig­ aspects, but one of the most important nificant points of impression: points to be resolved was the height of the 1. The metrical analysis of the photo- METRICAL PHOTOGRAPHY 677 graph gave him rejuvenated confidence in raphy as a universally recognized service the case. tool to science, engineering, and industry 2. He did not realize the degree of ac­ will be dependent not only upon the status curacy obtainable by means of photogram­ of our technical competence, practical ex­ metrical analysis. perience, or fineness of instrumentation, 3. Without the metrical analysis of the but also upon our ability to understand photograph he had no support and there­ people and their requirements, so that the fore no means to refute contributory negli­ problem can be clearly stated and the solu­ gence as to the altitude and attitude of the tion.satisfactorily performed. aircraft. 4. The fact that film can be exposed, de­ ACKNOWLEDGEMENTS veloped, stored, and years later removed Grateful acknowledgement is extended for a metrical analysis. to Mr. C. J. Williamson for editing the Inasmuch as the science of photogram­ manuscript and Mr. J. S. Rosenfield for metry is not well known, budgets to pur­ preparing the art work. sue metrical photography projects are usu­ ally nonexistent or very meager. Even REFERENCES when metrical photography is recognized (1) Burns, Charles, "'3-D' in Research." as the means of performing the measure­ Photographic Image. Ilford, London, 1956. ment survey, the capitalization of record­ (2) "Collier's Encyclopedia." Vol. 15, P. F. ing and reduction instrumentation may ap­ Collier & Son Corp., New York, 1950. pear to some to be relatively high. A vi­ (3) Gordon, J. W., "Generalized Linear Per­ cious cycle or round-robin appears to exist. spective." Constable & Company, Ltd., London, 1922. Manufacturers cannot anticipate all the (4) Gruber, O. von, editor Photogrammetry. special applications of metrical photogra­ American Photographic Publishing Co., phy and, if they could, the many and Boston, 1942. varied applications may not be compatible (5) Lacmann, Otto, "Die Photogrammetric for standardization and production of in ihrer Anwendung auf nichttopographi· stock items in the interest of more attrac­ schen Gebieten." S. Hirzel Verlag, Ger­ tive pricing for the potential user. In the many, 1949. meantime, the potential user must either (6) McNeil, G. T., "Photographic Measure­ improvise, modify, utilize existing com­ ments." Pitman Publishing Corp., New York, 1954. ponents, or procure a custom-made sys­ (7) McNeil, G. T., "Tilt by the Graphical tem. As we are all aware, custom-made Pyramid Method." PHOTOGRAMMETRIC systems can be many times more expen­ ENGINEERING, Vol. XII I, No.3, Washing­ sive than an equivalent production item. I ton, September 1947. would hesitate to venture a guess as to the (8) Miskin, E. A., "The Applications of cost of one of our popular automobiles if it Photogrammetric Techniques to Medic,fll were custom-made. Possibly an initial Problems." The Photogrammetric Record, solution to the capitalization problem for Vol. II, 10 . 8, London, October, 1956. organizations with limited budgets is one (9) Ragey, Louis, "The Work of Laussedat." PHOTOGRAMMETRIC ENGINEERING, Vol. that has been utilized before in other fields XVIII, No.1, Washington, March 1952. under similar circumstances, and that is (10) Saint-Exupery, Antoine de, "Wind, Sand for one organization to capitalize the in­ and Stars." Harcourt, Brace and Co., strumentation, conduct comprehensive New York, 1949. metrical photography research, and offer (11) Weaver, Warren, editor "The Scientists the service to others. Speak." Boni & Gaer, Inc., New York, The establishment of metrical photog- 1950.