CHAPTER XXXIII

EXPLORATION AND MAPPING

Aerial photographic mapping in war-time has been almost entirely confined to inserting new details in old maps. For such work some distortion or a lack of complete information on altitude and directions is not a serious matter, because the known permanent outlines serve as a basis. Furthermore, in so far as outline maps are concerned, as distinguished from pictorial maps, these have been drawn on the ordinary scales, and with the ordinary conventions of engineering map practice.

Aerial photography may be used in the future in practically the same way, as an aid to the quick recording of those minute details which would ordinarily consume an enormous amount of labor to survey directly. The region shown in Fig. 200 affords a good illustration. A discouraging amount of time and effort would be required to map this section of Virginia by the usual methods, while the smallest curve of creek and shore is instantly and completely recorded on a single photographic plate. But there are other possibilities, diverging from this application both toward greater and lesser requirements for precision.

Pictorial maps, in which the actual photographs figure, promise to be an essential part of the airman's equipment, whether he be pilot or passenger, mail carrier or sportsman. Without any pretention to detailed accuracy of location, these maps will show, in strip or mosaic form, the general appearance of the country to be traversed, with particular reference to good landing fields and other points of interest to the aviator. Vertical pictorial maps may be supplemented by obliques giving the view ahead, whereby the pilot may direct his ship. Thus the Washington monument as seen by the pilot from Baltimore is a truer guide than is the country beneath him. The crossing of mountain ranges is another case where the oblique picture will be more useful than the vertical (Fig. 201).

Contrasted with the merely pictorial maps will be precision surveys. Whether it will prove practical to make these entirely from the air is still an open question. It is to be assumed that cameras can be constructed with lenses having negligible distortion of field, with between-the-lens shutters to obviate the distortions due to the focal-plane type, with auxiliary devices for indicating compass direction, altitude, and inclination, or with gyroscopic mounting so that an inclination indicator is unnecessary. The application of aerial photography to precision mapping will depend upon the perfection which such cameras attain, as estimated by the permissible errors in this form of mapping. Entire dependence on photography, as in uncharted regions, is likely to be worked up to slowly, beginning with a stage of rather complete triangulation of natural or artificial points—say three in each constituent picture—then through several stages each successively employing fewer and fewer well determined points. The photographic mapping of some of our Western States will be greatly facilitated by the 100-yard squares into which the land is divided and already marked in a manner which shows clearly in aerial photographs.

A theoretical possibility is the plotting of contours from stereo-aerial pictures. Given two elements of a stereoscopic pair, taken from points whose separation is known, the position of any point in space shown in the stereoscopic view can be determined by the use of the stereo-comparator. This is an instrument already employed in mountain photo-surveying, which consists essentially of a compound stereoscope in whose eye-pieces are two points movable at will so that the relief image formed by their fusion can be made to coincide with any chosen part of the landscape. The chief difficulty in the application of this idea to aerial work is to fix the base line. This problem may be met in some cases by using stereo obliques, and getting the base line by simultaneously made vertical photographs of well surveyed territory beneath. Possibly also methods can be developed by which photographs from two or more known altitudes may furnish the requisite data.

City mapping is a field for which aerial photography is peculiarly fitted (Fig. 202). A complete map of a large city is a labor of years. In fact, a modern city is always dangerously near to growing faster than its maps. An aerial map, on the contrary, can be produced in a few hours. Paris was mapped with 800 plates in less than a day's actual flying. Washington was completely mapped in 2½ hours, with less than 200 exposures. The entire map is shown, on a greatly reduced scale, in Fig. 203, while Fig. 204 shows a small portion of it in full size, from which can be obtained an idea of the dimensions of the original. These maps, while not accurate enough for the recording of deeds and mortgages, yet serve the majority of needs. There is indeed no reason why with long focus cameras, given several accurately marked points, the photographic map of a piece of real estate should not be made with all the accuracy needed, still leaving the whole process of partial surveying helped out by photography an enormously simpler one than the usual method.

Rougher types of surveying, in open country, offer a most promising opportunity. Railway surveys, showing the character of the country: passes through mountain ranges: the available timber and other materials of construction. Canal routes, with the available sources of water supply, and the best choice of course to avoid deep cuttings and aqueducts. Irrigation projects, with the natural lakes, river courses and valleys, which may be dammed to form storage basins. Coast, river and harbor surveys are possible by aerial means with a promptness and frequency which should entirely revolutionize the making of maps of waterways. Shifts in channels and shallows, even of considerable depth, stand out prominently in the aerial photograph. The actual bottom, if not more than three or four meters down—as in a bathing beach—shows in the aerial photograph (Fig. 193), while the varying surface tints caused by light reflected from the bottom at far greater depths are readily differentiated by the camera from the air. An instantaneous photograph will thus perform the work now done by a week's soundings. Fig. 205, taken near Langley Field, shows how the aerial photograph may be used to chart natural channels, while Fig. 206 shows the dredged channels of the port of Venice. Navigation of such a river as the Mississippi with its shifting bars may come to be guided by monthly or even weekly aerial photo maps.

Among other uses for aerial photography will be the location of timber. As one illustration, may be taken the discovery of mahogany trees. Their foliage at certain times of the year is of characteristic color. This may be recorded on color sensitive plates with a scientifically chosen filter, and the cutting expedition sent out with the photograph as a guide. In this as in other cases where rough or unexplored country is to be covered, it is a question whether the airplane will after all be the most feasible craft, on account of its necessarily rapid rate of travel, and its need for known landing fields. The dirigible of large cruising radius, which can seek its landing field at leisure, is probably indicated for this kind of work. It may indeed, as already hinted, prove to be the chief photographic aircraft of the future.

Archæological surveys offer a fascinating opportunity for airplane or dirigible balloon photography to render scientific service. Buried in desert sands or overgrown with tropical vegetation the ancient cities of Asia Minor, of Burma, and of Yucatan evade discovery, and even when found remain unmapped for decades. Discovery and mapping can now go hand-in-hand. The topography of barbaric or colonial towns and villages, whose importance could not warrant elaborate surveys, but which should nevertheless be a matter of record, will be quickly and easily plotted by photography (Fig. 207). To this day who knows how the streets run in Timbuctu, and how, save from the air, can we ever map the teeming cities of China? He who would follow in the footsteps of Haroun-al-Raschid can even now explore the by-ways of Bagdad by the aid of the Royal Air Force photographic map!

INDEX

Aberrations, lens, 47, 54

Aberration, spherical, 47, 54 chromatic, 48, 54

Acetylene light, 284

Advertising, use of aerial photography in, 392

Aero 1 and Aero 2 filters, 241

Airplane, as camera platform, =20= types of, 24

Air speed, 27, 308 indicator, 33, 34

Alcohol, use of in plate drying, 275 use of in print drying, 286

Altimeter, 33, 174 reading recorded on film, 135, 171

Altitudes of flight for photography, 61, 224

Anastigmatic type of lens, 47

Aperture, lens, 39, 44, 56, 57

Archæological surveying, 413

Astigmatism, 49, 50, 54

Auxiliaries, camera, =163= installation of, 214

Bagley camera, 286, 314

Balance, of camera, 96 of plane, 157, 208, 217

Balloons, 15, 16, 18

Banking, 27, 324

Batteries, storage, 150, 156

Bay, camera, 120, 210

Bellows, camera, 65, 95

Biplane, 24

Blast marks in front of guns, 363

Bleaching out print to leave interpretation marks, 367

Boat, flying, 25, 374

Bowden wire, 103, 106, 108, 111, 114, 116, 118, 126, 129, 136, =163=

Brightness, range of, 221, 225

Burchell photographic slide rule, 303, 339

Camera, airplane, =39=, 384 automatic, 18, 43, 90, 116, =124=, 125, 311 B. M., =120=, 203 Bagley, 286, 314 Brock automatic plate, =126= C type, 43, 87, 103, =109= classification of, 43 deMaria, 86, 89, 103 deRam, 82, 93, =121=, 129, 157, 205, 214, 326 E type, 43, 87, 103, =109= elements of, =42= film, _see_ Film cameras Folmer automatic plate, =126= hand held, =95=, 321, 369 English, =99= German, =99= U. S. Air Service, =100= Ica, =103= Lamperti (Italian), =112=, =211= L. B., =120= long focus, 103, 301, 324 L type, 43, 82, 94, 102, =117=, 162, 210 M., =106=, 203 non-automatic, 43, =102= Piserini and Mondini, =111= semi-automatic, 43, =116=, 149 stereoscopic, 341

Camouflage, filters for the detection of, 225, =243= stereoscopic views and, 329, 358

Ceiling of plane, 27, 130

Channels, detection of by photography, 408

Chemicals, photographic, =257=

Chlorhydrochinon developer, 261

Chromatism, lateral, 49, 54

City planning, use of aerial photography in, 396

Clock-work for driving cameras, 149, 155

Clouds, 224, 242

Collimator, 66

Color, coefficient or index of negative, 259 filters, _see_ filters photography, =385= sensitive plates, 15, 174, 233, 237 sensitiveness of film, 131 sensitizing, methods of, 235

Coma, =47=, 48

Communication, means of on plane, 296

Compass, 33, 173 reading recorded on film, 135, 171

Cone, camera lens, 42, 114 interchangeable, 108, 120

Construction operations, aerial photographic records of, 396

Contact, imperfect in printing, 279, 284 prints, 45, =279=

Contacts, electric, on plane, 163

Contours by stereo aerial photography, 404

Control, distance, of camera, 110, 163 speed, of camera, 136, 144, 157

Controls, duplicate, 19, 25, 195, 209, 214 of plane, 21, 26

Convergence point, 337

Cord for adjusting shutter aperture, 82

Core rack development, 271

Contrast, in brightness on earth's surface, 221 in photographic emulsions, 15, 230, 236, 258

Counter, exposure, on magazine, 88 on release, 164

Covering power of lens, 44, =49=, 50, 58

Crabbing, 27, 308

Cradles, camera, 195

Cross wires, 23 insertion of camera through, 42, 210

Curtain, auxiliary shutter, 80, 84, 106 speed of travel of shutter, 74 uniformity of, 76, 82, 84, 86, 315

Cylinders, relation between vibration and number of, 185

Dark slides, double, 87, 99

Daylight, intensity of, 222

Definition, lens, 44

Density, of air, effect of on propeller, 154 of photographic image, 228

Developers, for plates and films, =257=, 260 for papers, =262=

Developing machines, film, 133, =273= Ansco, 273 Brock, 274 Eastman, 274 G.E.M., 273

Development, core rack method of, 271 factor, 228 film, =272= methods of, =267=, 269 of prints, =286= speed of, 236, 267 tank, 270 time, 269

DH-4 plane, 210, 217, 296 photographic, 213

DH-9 plane, 296

Diaframs, to equalize illumination of plate, 78 lens, 48, 58

Dilution coefficient of developer, 258

Dirigibles, 15, 16, 413

Distortion, absent with between-the-lens shutter, 74 barrel, 51 due to camera tilting, 206, 286, 305, 315 in aerial maps, 317 lens, 39, 44, 51, 54, 56, 62 pin-cushion, 51 produced by film shrinkage, 237 produced by focal plane shutter, =74= produced by glass plate in front of film, 131 with wide angle lenses, 63 “Dodging” in printing, 279, 315 Doors in plane for camera to work through, 214

Drying of films, =267=, 276 of plates, 267, 275 of prints, =286=

Earth, appearance of from plane, 30

Eastman apron film developing machine, 274 twin reel film developing machine, 274

Efficiency, propeller, 155 shutter, 70, =72=, 76

English aerial photographic practice, 45, 46, 283, 291, 340

EK filters, 241

Electric, drive for cameras, 116, 119, 123, 145, 149 generator operated by motor, 146 motor, characteristics of, 151, 156 motor, service, 163

Elevation possible to detect in stereoscopic views, =340=

Emulsions, photographic, characteristics of, =227=

Enlarging, 45, =279=, 283 camera, 283

Enlarging versus contact printing, 59

Exhaustion of developer, 259

Exploration, use of aerial photography in, 401

Exposure, data charts, 250 distance between for mosaic maps, 307 distance between for stereos, 336 estimation of, 248 limitations to, 247 meters, 251 meter, Wynne, 251 of aerial negatives, =247= relation between motion of plane and, 68, 185 under, period, 230

Field, angular, of lens, 57, 302 flatness of lens, 56

Field laboratory, mobile, 268

Film cameras, 43, =130=, 134 Brock, 138 Duchatellier, 131, 136 F type, 134, 171 G.E.M., 138 German, 64, 76, 139, 317 K type, 142, 203, 214

Film, celluloid, 130 backed, 133 changing in the air, 137, 144 color sensitiveness of, 237 cut, 275, 278 development of, 130, 272 drying, 131, 276 means for holding flat, 130, 131 relative performance of compared to plates, 237 satisfactory kinds for aerial work, 238 shrinkage, 237

Filters, 15, 58, 106, 174, 224, 233, =239=, 241, 243 effects secured by use of, 241

Filters, gelatin, 244 glass, 245 holders for, 67, 106, 224 ratio, 240

Fixing bath, 262

Flaps, auxiliary to shutter, 80, 84, 85, 98, 99, 101, 119 to protect lens, 214

Flash lights, 18, 386

Flying boat, 374

Focal length, relationship of lens characteristics to, 55, 57 requirements for, 39, 42, 58, 61, 103

Focal plane, 50 shutter, 70, 71 distortion by, 74 performance of, 86 types and representative, 80

Focus, depth of, 44 effect of temperature on, 41, 65 fixed, in aerial cameras, 40 ground and air, 65

Focussing, automatic, 284 by parallax, 65, 66

Fog, atmospheric, 224 photographic, 237, 258

French aerial photographic practice, 45, 46, 283

Friction disc speed control, 136, 159, 160

Fuselage, 21, 87 shape and size depending on type of engine, 23

Future of aerial photography, =383=

German aerial photographic practice, 63, 103, 209

Glass, optical, used in lenses, 44

Gloves, handling apparatus through, 41, 89

Governor for camera speed, 159

Graphite, use of to prevent static discharge, 134

Gravity, action of in aerial cameras, 41, 112, 115, 119 center of, should not change in cameras, 125, 207 change of center of, in magazines, 92, 112 depended on in magazines, 88 handles best at center of, 96 pseudo, in moving vehicle, 188 support at center of, 182, 203

Ground speed, 27, 307 indicator, 311

Guide-books, illustration of, 15, 392

Guides for inserting magazines, 41

Gyroscope, 189

Gyroscopically controlled instruments, 29, 174, 192, 312

Gyroscopic erector, 188 mounting of camera, 187 stabilizer, Gray, 190

Hardener, acid, 262

Hand operation of deRam camera, 121, 125, 129

Haze, 15, 30, 223, 233, 239

Head resistance and weight, equivalent, 156

Heat, effect of on plate sensitiveness, 175, 232

Heater, electric, in camera, 142, 174, 232

Horizon, photography of to indicate inclination, 174 position of, 30

Hurter and Driffield sensitometric curve, 227

Illumination of field by lens, 50, 54, 56, 57

Image of point source, size of, 49, 54, 56 size of in relation to focal length, 59

Incidence, angle of assumed by plane at high altitudes, 206

Inclinometer, 33, 35, 171, 173

Indicators, distance, 163, 295

Inertia, 229, 257

Installation, camera, 24, 208

Instructions, operating, to be placed on apparatus, 42

Instruments, airplane, 30

Instrument board, 30 photographing, 170

Intensification of aerial negatives, 262

Intensity of daylight, 222

Interpretation of aerial photographs, 17, 40, 351

Interval between exposures, 40, 158, 305, 307 for stereoscopic pictures, 334, 338 methods of regulating, 124

Isochromatic plates, 233

Italian photographic practice, 122, 377

Jamming of cameras in operation, 119, 120

K_{1} and K_{2} filters, 239

Keeping power of developer, 259

Kites, 15, 16, 18

Laboratory, mobile photographic, 269

Landscape gardening, use of aerial photography in, 395

Latitude of plates, 229

Lens, 42, 39, =44=, 383 aperture, 39 characteristics, 46 mounts, 65 suitable for aerial photography, 62 symmetrical, 52 telephoto, 61 testing and tolerances, 52 unsymmetrical, 52 wide angle, 62

Levels, spirit, on camera, 95

Light, distribution of in aerial view, 221 trail method of testing camera mountings, 183

Loop, centrifugal force in, 29

Machine gun ring as camera mount, 321

Magazines, =87= bag, 88, 101 Bellieni, 92 Chassel, 92 deMaria, 89, 98 Ernemann, 89 Folmer, 90 Fournieux, 92 Jacquelin, 92 Piserini and Mondini, 90 Ruttan, 92

Magazine racks, 94 installation of, 217

Mapping, 64, 135, 185, 186, =304=, 401 precision, 317, 404

Maps, mosaic, 17, 39, 64, 314 sketch, 314

Marking of negatives, 278

Metol-hydrochinon developer, 261

Mirrors for oblique photography, 324, 326

Monoplane, 24

Motions of camera, 179

Motive power for aerial cameras, =145=

Mounting, camera, 102, =103=, 179, 183 384 bell-crank, 120, 198, 203 Brock, 139, 207 center of gravity, 205 floor, 195 G. E. M., 138, 207 Italian, 207 outboard, 194 parallel motion, 198 pendular, 185 tennis ball, 196

Mounting, camera, turret, 312 of prints, 316 of stereograms, 346

Movement, of film during exposure, 75, 142 of image, permissible, 68

Moving pictures from plane, 350

Mud splashing on camera, 214

Naval aerial photography, =368=

Negative lens sight, =168=, 299, 305

Night photography, =386=

Numbering devices in cameras, 169

Oblique views, 39, =320= angles at which taken, 40, 321 exposures for, 69 filters for, 242 use of hand cameras for, 95

Observer, function of in aerial photography, 291, 295, 304

Oil spray from motor, 214

Opacity, 228

Opening for camera, 211

Opposite directions, shutter to move alternately in, 76, 139

Orthochromatic plates, 233

Overlaps, for mapping, 307 for stereoscopic views, 40 on a turn, 64, 139

Panchromatic emulsions, 233 plates, 49, 238

Panoramic views, 321

Parallax method of focussing, 65, 66

Parallel, flying in, 308

Photographic planes, special, 213

Pilot, function of, in aerial photography, 291, 295

Pinpoints, 39, 291

Pistol grip for hand cameras, 95, 96

Plate holders, 87

Plates, bathed, 235 behavior of compared to film, 237 color sensitive, 233 iso- and ortho-chromatic, 233 panchromatic, 233 satisfactory kinds for aerial work, 238 self screening, 245 shape of, 63 size of, 43, 62

Plumb line, behavior in banking plane, 28

Ply-wood veneer construction, 23, 211

Positype paper, 238

Potassium carbonate for drying plates, 276

Power required to drive cameras, 125

Pressure, of shutter curtain, 131 plate, for holding film flat, 131, 141

Printing, =279= contact, 279 machines, 279 media, 252

Prints, paper, 253 development of, =286=

Prisms for oblique photography, 324, 326

Propeller, characteristics, 152 constant speed, 129, 159 drive for cameras, 102, 116, 119, 135, 136, 144, 157, 158 position of, 120 variable speed, 159

Pump, for producing suction on film, 132

Punch marks on film, 144, 272

Pyro developer, 261

Racks, negative, 271

Real estate, aerial mapping of, 393

Rectifying, 286, 305 camera, 314

Reduction of aerial negatives, 262

Release, shutter, 96, 99 duplicate, for pilot, 164

Release, shutter, time controlled, 124

Relief, criterion for correct, 335, 344 exaggerated, 337 impression of, produced by motion, 349

Resolving power of plates, 59, =235=, 260

Richard stereo printing frame, 283, 348

Rinsing of plates, 259

Rubber, sponge, use of in camera mountings, 195, 203

Safe lights, photographic, 269

Safety catch on camera mounting, 203 device on camera driving mechanism, 162

Salvaging of ships, aerial photography and, 399

Seaplane, 25, 374

Self screening plates, 245

Semaphore signalling in plane, 297

Semperfocal enlarging camera, 284

Sensitized materials, requirements for, 225

Sensitometry, =227= of papers, 253

Shadows, compass directions from, 356 proper direction for, in examining prints, 352

Shaft, flexible, 119, 123, 142, 161

Sheaths, plate, 87, 88, 93, 126, 170

Shrinkage, film, 237, 317 paper, 285, 315, 317

Shutter, 42, 68 between-the-lens, 58, 70, 112, 115, 316, 387 efficiency, 70, =72=, 76 focal plane, 70, 71, 73 focal plane, double for stereo work, 341, 345 focal plane, moving alternately in opposite directions, 76 focal plane, types of, 80

Shutter, Folmer, 80 Ica, 81 Klopcic, 78, 84, 98 release, 96, 99, 124 speed, 39, 40, 58, 70, 249 testing, 76 testing apparatus, 77

Sights, =164=, 166, 296, 301, 327 adjustable for angle of incidence of plane, 169 attached to plane, 167 negative lens, 168, 299, 305 rectangular, 98, 167, 373 stereoscopic, 338 to indicate size of field, 166, 373 tube, 101, 166

Single-seaters, carrying cameras in, 114, 211

Slide rule, photographic, 303, 339

Solenoid, 151, 163

Sound, not to be used for indication in plane, 164

Spacing of pictures in film camera, 144

Speaking tubes on plane, 296

Speed, of development, 236, 267 of plates, 228, 236 criteria of, 230 effect of temperature on, 175, 232 variable, control of camera, 144, 151

Spotting, 64, 125, =291=

Spring motors, 149, 155

Springs, use of in aerial cameras, 41 in magazines, 88

Stabilized camera, 95, 187

Static electric charges on film, 131, 133

Stereo-comparator, 404

Stereo-oblique views, 115, 321, 343

Stereoscopes, 331

Stereo printing, 283

Stereoscopic cameras, 341, 344 effect, absence of at flying heights, 30, 334

Stereoscopic photography, 329 mounting, 346 pictures, fusion of without instruments, 330, 343 sights, 338 views, 39, 40, 64 uses for, 348 vision, principles of, 329

Stop-watch attached to shutter release, 310

Strap, on hand camera, to go around observer's neck, 99 on plate magazine, 87 to go over hand, on hand camera, 100

Stream lines, 26 lined hood, 214

Suction for holding film flat, 131, 132, 142 advantages of continuous and intermittent, 132

Surveying by aerial photography, 401

Tank development, 270

Tearing edges of prints, 317

Telephones on planes, 296

Telephoto lens, 61

Temperature, coefficient of development, 258 effect of on focus, 41 effect of on mechanical functioning, 41, 102, 125 effect of on plate speed, 232 limits of development, 258

Test chart, lens, 52

Threshold value, 230

Thrust, propeller, 152

Timber, location of by aerial photography, 413

Tone rendering, correct, 226, 230, 239

Touch, sense of, not dependable in plane, 41, 125, 164

Trailer, photographic truck and, 268

Transmission of power to camera, 161

Transparencies, 252, 330

Transparency, 227

Trays, camera, 195

Tri-color ratio, 235

Triplane, 24

Tuning fork, used in shutter tester, 79

Turbine, wind, for driving camera, 116, 127, 144, 147, 158

Uniformity of curtain speed in focal plane shutter, 76, 82, 84, 86, 315

Unit system of camera construction, 42

Uprights, camera, in plane, 209

Uses for aerial photography, =388=

Velocity constant, 258

Veneer construction, 23, 209, 211

Venturi tube, 132, 142, 144

Vibration, 16, 18, 26, 40, 41, 58, 102, 179

Volcanoes, photography of, 15, 399

Water for mixing chemicals, 262

Watkins factor, 258

Weight and head resistance, equivalence, 156 of film compared to plates, 101, 130 of deRam camera, 123 of hand cameras, 96 of K type camera, 144 of K film roll, 144 of L type camera, 117 of M type camera, 109 of storage batteries, 157

Wind, flying against, 68, 308 motor, 146

Windows in side of plane, 214, 328

Wire, barbed, appearance of in aerial photograph, 360

* * * * * *

Transcriber's note:

1. Silently corrected typographical errors.

2. Retained anachronistic and non-standard spellings as printed.