D. GUTJ. HOHLE

Wild Heerbrugg LimitedHeerbrugg, Switzerland

High Altitude Photography:Aspects and ResultsLarge area coverage, combined with the use of highresolution cameras and precision stereoplotters, provides foreconomical mapping procedures.

INTRODUCTION

I N PRACTICAL PHOTOGRAMMETRY a singlephotograph is used to cover as large an

area as possible while maintaining recogni­tion of detail and geometric accuracy neces­sary for topographic mapping. Small jet air­craft enable the photogrammetrist to attainimage scales of up to 1: 150 000. Both of the

duction with modern instruments on thebasis of the results obtained from the testfield photographs.

GENERAL ASPECTS OF HIGH ALTITUDEPHOTOGRAPHY

PHOTOGRAPHIC AIRCRAFT

Recently, very high flying small jet aircraft

ABSTRACT: Cameras equipped with the most recently developedlenses from Wild Heerbrugg Ltd. were used to take aerial photo­graphs from small jet aircraft over the test range at Casa Grande,Arizona. Aircraft, flying height,field angle, and photographic emul­sion were varied in the tests. Numerous stereopairs were evaluatedin a precision plotter and under a P.l. microscope. The height accu­racy obtained from 15 em (6") focal length lenses was 0.004 percentof the flying height or one part in 25 000, which is a new achieve­ment in analog photogrammetry. Systematic effects varying withaltitude were detected, and a method for compensation was de­veloped. Ground resolution was better than 2.5 m on the ground forthe maximum flying height of 13.4 km (44 000 ft.).

The enormous area coverage, combined with high geometric accu­racy and ground resolution of high altitude photography, permit theuse of new procedures in aerotriangulation, and in small-scale lineand ortho-photo mapping. Some proposals for new procedures inthese fields of application are made. Other aspects of high-altitudephotography, such as automatic navigation, semi-automatic opera­tion of a dual camera system, camera performance, and installationrequirements, are discussed as well. The four photographicairplanes tested are now in use in South America.

authors have installed camera systems andparticipated in jet test flights. Numerousphotographs were taken by D. Gut over atest field. The image material was analyzedwith regard to geometric accuracy and imagequality. The purpose of this paper is to showthe unique characteristics ofjet photographyand to determine the potential for map pro-

with pressurized cabins have been used re­peatedly by civil organizations and privatecompanies for aerial photography. The Lear­jet of the Gates Learjet Company (USA), forexample, has a service ceiling up to 13.7 kmalong with other advantages important forphotogrammetric application. The highrate-of-climb performance (in less than 20

PHOTOGRAMMETRIC EGINEERING AND REMOTE SENSING,

Vol. 43, No. 10, October 1977, pp. 1245-1255.

1245

1246 PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING, 1977

minutes up to 12 km), the high velocity(about 800 kmlh), and the range of about 3000km rapidly bring the camera system to thetarget area at high flying heights. Large areasmay be flown over at equal illumimition andweather conditions. For photography atlower flying heights the maximum velocitycan be reduced to a third. The flight altitudeis stable and vibrations are slight. Con­sequently, there are only small tilts and theimage quality is primarily determined by thelens. The working conditions in the pres­surized cabin are very comfortable for theoperator. The camera is no longer exposed toexh'eme changes of pressure and tempera­ture. The necessary floor closing glass, how­ever, is palt of the image system. Its quality.also determines the quality of the photo­graph.

INSTALLATION OF THE CAMERA SYSTEMS

First of all the installation of a window isnecessary in pressurized aircraft. Its dimen­sions are determined by the field angle ofthe lenses used, the position of the entrancepupil, and especially by the security regula­tions. In the Gates Lealjet Model 25 C, forexample, 508 x 584 x 38 mm3 windows areinstalled for the RC-10 equipped with asuper-wide-angle lens. The optical quality ofthe windows must be adapted to that of thelenses and filters in order to keep geometricand optical errors small. The two surfacesmust be parallel. Deflection of the glassplate causes distortion. The cameras havedifferent lenses, suspensions, viewfinders,and navigation telescopes. For installation ina jet the most f~1Vorable components have tobe chosen and special measures have to betaken. For the Aviophot System of Wild thefollowing general aspects are of importance:

• The window dimensions are to be fixed forthe lens with the largest image angle. Iflenses with a smaller image angle are alsoused, a spacer has to be used in order toclear the lens cone fi'om the window.

• The rotation of the camera for the purposeof the drift, tip, and tilt correction and itstilting for the change of filters require spe­cial distances to the side walls and insidesetups.

• For the exclusive use of the super-wide­angle lens a suspension of low height canbe used. The entrance pupil of the lensthus comes as near as possible to the win­dow; its size can then be kept smaller thanwhen using the standard suspension.

• For navigation, drift, and overlap control,the viewfinder telescope can be installedbehind a window. It also can be prepared

for simultaneous control of a second cam­era (slave camera).

In the Learjet the door of the airplane hasbeen modified for a single camera and canrapidly be exchanged against the standarddoor. 1 For the double camera two windowslying side by side have been installed (com­pare Figure 1).

Often navigation of a jetplane is no longerperformed with the viewfinder or navigationtelescope, which merely control overlap.The Inertial Navigation System, e.g., theINS-61B of Collins Radio Company or theLTN-51 of Litton Industry, and its couplingwith the autopilot hold the aircraft automati­cally at a very stable altitude along the de­sired flight path. Only the coordinates of thewing points of the flying pattern have to bekeyed into the computer of the INS.Moreover, the drift angle of the aircraft isindicated and can be transferred to the cam­era manually.

PHOTOGRAPHIC PROBLEMS IN HIGH-ALTITUDE

PHOTOGRAPHY

Systematic errors affect photographs takenthrough a window at high altitudes. Theseerrors are named and estimated according totheir size and their consequences.

Earth curvature. Elevations determinedby geodetic surveying relate to the roughlyspherical plane of mean sea level. Con­sequently, the photogrammetric instrumentalso must have a spherical reference plane orother means of compensation. If no provi­sions for compensation are incorporated inthe stereoplotter, the photogrammetric mod­els will be warped. Warping depends on theflying height and the focal length of thecamera. The errors are high, as illustrated inFigures 2 and 3.

Atmospheric refraction. The index of re­fraction of air decreases with increasing al-

FIG. 1. Dual camera installation in the Learjet.

HIGH ALTITUDE PHOTOGRAPHY: ASPECTS AND RESULTS 1247

FIG. 2. Influence of earth curvature on the imageposition of a wide angle photograph if = 153 mm)as a function of the flying height. The linear por­tion (scale) has been removed in that presentationas distOition.

titude due to changes in temperature andpressure. The imaging ray will be bent andthe image point displaced towards the imageedge. However, the errors are very small andof opposite sign to that of the earth curvature

(Figures 4 and 5).Window flexure and change of refraction

index of air. At high altitudes temperatureand pressure are very different on the twosides of the window. The resultant Hexure ofthe window and difference in the refractionindex of air produce a displacement of theimage. However, the amount of the dis­placement is very small if the window ismanufactured and installed properly (Fig­ures 6 and 7).

Change in focus and calibrated focallength. In general, lenses with longer focallengths (f=305 mm,f=213 mm) are focusedby the manufacturer to finite object dis­tances, for example, to 850 m at the WildAviotar At II. If the lenses are used at highaltitudes, the resolving power may decreaseunder certain conditions. Especially the 305mm lens is critical when maximum apertureand black-and-white films of high resolvingpower (e.g., Kodak Plus X) are used at al­titudes above 4 km. In this case the use ofsmaller apertures or special focusing onlonger object distances is recommended.The above-mentioned image displacementsdue to window Henue and atmospheric re­h.·action lead to a change of the calibratedfocal length. These values are smaller than0.02 mm and can be neglected in most cases.

[mmJ

~..~.

• 5km.-'40

20

30

10

- SO

- 20

- 10

- 40

- 30

max. hei hterror

Iml

10

r%0 hI'-----------1+-0--------1+S-f-1,;.,Y..i ng [::;9ht h

flying height h

S 10 lS [kml

FIG. 3. Maximum vertical errors in the middle of the neat model dueto earth curvature as a function of flying height and focal length. For­ward lap 50 percent, sidelap 0 percent, control points in the four cor­ners of the model.

1248 PHOTOGRAMMETRIC ENGI EERI G & REMOTE SENSING, 1977

d'

- J

.~l-.,

./0

I •• - 1

- 2

- 3

- 4

Imj

FIG. 4. Displacement of the image due to atmo­spheric refraction as a function of the image radiusand the flying height. Values are based on awide-angle photograph if = 153 mm).

PRACTICAL TESTS

The functional tests of the Learjet photo­graphic aircraft:, which are carried out on aroutine basis, include taking photographyover a test range. In the last two-and-one­half years several tests have been performedin which aircraft, camera, lens, altitude, andseason were varied. Numerous stereopairshave been evaluated with respect to geomet­ric accuracy and image quality. From thisexperience the current procedures in map­ping at small and medium scales shall beexamined. The conditions during the testsshall first be explained.

PHOTOGRAPHIC AIRCRAITS

The Lealjet models 24 D, 25 B, 25 C, and35 C were used. A single camera was install­ed in the interchangeable door or a doublecamera in the fuselage. In the latter case asliding door protected the windows duringtake ofT and landing. The window was a 51cm x 58 cm x 3.8 em Schott BK 7 glass plate.The pressure inside the cabin correspondedto the pressure at an altitude of 2 km.

TEST RANGE

The 25 km x 25 km Casa Grande test

FIG. 6. Displacement of the image due to win­dow flexure and difference of the refraction indexof air at both sides of the window. (Calculationwith the following parameters according to refer­ence 2: Index of refraction of glass n = 1.517,temperature inside cabin T = 20°C, pressure in­side cabin corresponding to an altitude of 2 km,window dimension 58 x 51 x 3.8 cm3 , ElasticityModul of glass 0.7' 106 kp/cm2 , focal length oflensf = 153 mm, position of entrance pupil of the lensabove window ISO mm)

range near Phoenix, Arizona was used. Itsdensity of control points, one target per 2.6km2 , and the shape of the panels allow mea­surements with photography of varying andextremely small scales. The target (see Fig­ure 8) has four quadrilateral "pointers," theparallel sides of which measure between 0.8m and 4.9 m. The smallest visible image dis­tance in the photograph can be determinedapproximately with the help of this panel bya simple procedure (see Figure 15).

Camera system. For photography, theWild Heerbrugg Aviophot System was used.The main part of the system is the RC 10camera, in which six lens cones can be intro­duced. In the tests the following lens coneswere used:

• the super-wide-angle lens 8.8SAG II, f =88.5 mm, Amax = 5.6

• the wide-angle lens I5UAG I,f = 153 mm,Amax = 5.6

/lt1lllall 1m

] f .. 153 llIIl

I'" hi0.6 ~/.

~ 0.05 0.5 /~

0.4 ~:r-'- 0.03 O.~.........--....................

0., ,//

• 0.01 0.1

.lhm.tx

I'" h] Iml( .. 153m. -'+ 0.03 o.3~:>, < - .

.0.02 0.2 _---.--

• 0.01 0.1--

FIG. 5. Maximum vertical error within the neatmodel of wide-angle photographs if = 153 mm)due to atmospheric refraction.

1513

10flyin9 height h

lkol

FIG. 7. Maximum vertical error within the neatmodel of wide-angle photographs if = 153 mm)due to window flexure and change in the refrac­tive index of air.

flying height h

(""I1513

10

HIGH ALTITUDE PHOTOGRAPHY: ASPECTS AND RESULTS 1249

5 m

FIG.8. Target of the Casa Grande Test Range. Itssize and shape are suitable for photography ofhigh-altitude and of vmying photo scales.

• the wide-angle lens 15UAG II,! = 153 mm,Am.x = 4

• the normal angle lens 21NAG II, f = 213mm, Am.x = 4

The last three lenses have been put on themarket just recently. The lenses have a verysmall distOition which causes a correspond­ingly small deformation of the stereomodel(see, for example, Figure 9). The singlecameras were controlled either by a naviga­tion sight or a viewfinder in a separatemount. The double camera used is shown inFigure 10.

Both of the cameras are controlled by onenavigation sight; they work simultaneouslyor independently with different lenses, over-

lap, and film. Using a dark yellow filter, twotypes of films, the panchromatic film KodakPlus X and the false color film Kodak Aero­chrome Infrared, were exposed. Exposurewas automatically controlled.

PHOTOGRAPHIC FLIGHTS

Test flights were carried out over the CasaGrande test range with four Learjets for gen­eral installation and camera tests and inorder to determine the geometric accuracy.Photographs of the test range were takenfrom altitudes of 5 km, 8.9 km, 11.9 km, and13.4 km on four different dates. Because thelens cones were exchanged during the tests,image scales between 1:33 000 and 1: 150000 were obtained. Navigation was carriedout with the Inertial Navigation System,with the help of which the drift angle wasobtained and manually transferred to thecamera-controlling navigation sight. Thismethod proved to be very practical and accu­rate. The overlap, however, was controlledin the usual way. For manual navigation theforward view of the navigation sight did nothave to be used at these altitudes. Therefore,the camera's viewfinder, installed in a sepa­rate mount, may be used as well. Its installa­tion and use behind a window pose no prob­lems.

- 1

- 2

[mml

MEASUREMENT OF PHOTOGRAPHY

The measurement of single models wascarried out on a precision stereocomparatorand on two precision stereoplotters, the WildSTK 1 and the Wild A 10, respectively. Theaverage elevation accuracy of the two analoginstruments used in the measurements is mil

nIll

30 60 90 r:rn

FIG. 9. Radial distortion of the wide-angle lensUAg II and the resulting height deformation (val­ues in micrometers and related to the photograph,overlap 61 percent). 3 /Lm = 0.02 °/00 h.

FIG. 10. Lemjet dual camera installation. Fromleft to right: master camera with 15 cm lens andspacer, navigation telescope with overlap reg­ulator, slave camera with 8.8 cm lens, circuitryunit, control unit, and exposure meter.

-3 -2 -2 -3

-3 0 0 -3

-2 1 -1 -2

0 2 2 -i0 0 0 0

0 0 0 1

0 0 0 0

0 2 2 -1

-2 1 1 -2

-3 0 0 -3

-3 -2 -2 -3

100

80

60

40

20

o20

40

60

80

100

RESULTS

GEOMETRIC ACCURACY

In Table 1 the measuring results of tensingle models obtained by the precisionstereoplotter are shown. They comprise theerrors of planimetry and elevation on theground and in the image.

Let us first discuss the results with theeight wide-angle stereopairs. The averageRMSE in elevation of ± 0.034 %0 of the flyingheight, or 1:33 000, is remarkably small. Thisis almost the limit of performance for mea­surement with an analog instrument. Themean errors of planimetry average mX,y= ± 10 /-Lm in the photograph. Consequently,the accuracy of planimetry is inferior to theaccuracy of elevation. The reason for this maybe the partially bad quality of the signals andthe resulting insecurity in setting themeasuring mark. Elevation setting could al­ways b~ done in the horizontal neighbor­hood of the target. The influence of the fly­ing height on the vertical error is shown inFigure 11.

The accuracy in elevation is best at thelowest flying height (mil = ± 0.026 0/00 ofthe flying height). At flying heights of 9 kmand more the accuracy of elevation is aboutthe same (0.038 °/00 of h). The elevation ac­curacy of the measured normal angle andsuper-wide-angle stereopairs is inferior tothat of the wide-angle stereopairs; itamounts to an average of mIt = ± 0.07 °/00 ofthe flying height. Better results for thesuper-wide-angle photographs can be ob­tained if compensation plates for lens distor­tion are used. When measuring thestereopairs, systematic model deformationsl!-P to about 0.2 %0 of the flying height werefound. This error, however, could largely becorrected by increasing the model scalenumber to be set in the compensation devicef:Or the ealth curvature. The magnificationfactors K, empirically found for the wideangle stereopairs, are shown in Figure 12; alinear dependence on the flying" heightexists. Some stereopairs also were evaluatedanalytically in order to detect the reason forthe systematic errors. The model deforma­tion was found to be of the same size (see inFigure 13). This fact proves the good ad­justment for the stereoplotter used and for itscompensation device for earth curvature.The reason for the deformation is very likelya higher flexure of the window during theflight than theoretically expected.

* Parameters of the instrument test are mea­surement of 66 grid points, f = 150 mm, Z

= 450 mm, bx = 300 mm, and MM = 1:100 000.

1250 PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING, 1977

= ± 0.021 %0 of the, flying height.* Thephotographs are observed at 8 x magnifica­tion. The instrument features a compensa­tion device for the influence of earth curva­ture. A sphere built in the model space iscontinuously scanned so that the referencein height will change with the position in themodel. The sensed value will be exagger­ated by a factor corresponding to the flyingheight or the model scale denominator.

If systematic errors of a spherical natureremain, the compensating efJect can be in­creased or decreased by changing the modelscale denominator. In this way systematicerrors in the stereo model, e.g., those due toatmospheric refraction, lens distortion, andflexure of the camera's pressure platen or theaircraft window, may be approximatelycompensated.

The revised model scale denominatorwhich is set in the correction device for eartl~curvature, has to be determined empirically.

The stereoplotter was equipped with adata acquisition device, the Wild EK 22,with connected desk calculator HP 9820.The coordinates and the elevations of eachpoint were measured three times. The aver­aged ,model coordinates were immediatelytransformed into ground coordinates at theside of the analog instrument. A simple spa­tial transformation over four conb'ol pointseliminates the small errors frequently aris­ing in manual absolute orientation. Thenumber and arrangement of control pointsvaried.

The stereocomparator STK 1 is an evenmore accurate measuring instrument (mX,y= ± 1 /-Lm). The measurement is done in amodel affected with parallaxes. The con­tinuous removal of vertical parallaxes at eachpoint calls for a high quality of the imagedtargets if the high accuracy of the comparatoris to be exploited. Systematic image errorssuch as lens distortion, earth curvature, re­haction, etc., are compensated for by calcu­lation. Determination of the coordinates ofthe test field was done with the help of acomputer.

The photointerpretation stereomicroscopeWild M 5 with parallel guided and illumi­nated picture carriages was used for a com­paring examination of the image quality. Thechosen enlargement of viewing was 12.5 x.The ocular was equipped with a rotatablemeasuring scale.

HIGH ALTITUDE PHOTOGRAPHY: ASPECTS AND RESULTS 1251

TABLE I. ACCURACY Of HIGH-ALTITUDE PHOTOGRAPHY

Aircraft Date Photo Scale RMSE2Control

Lens Cone Flying Height' Photo No. Pts. Terrain3 Photograph4

25C Sept. 74 1:33000 8 mE = ± 0.24 m = + 7x -15 UAgII 5000 ill 1345/46 fiN = ± 0.39 m" = ± 12No. 3035 (16400') mH = ± 0.13 m, = ± 0.026

25C Sept. 74 1:33000 8 mE = ± 0.23 m = + 7x -15 UAgII 5000 ill 1341/42 mN = ± 0.37 m,,=±11No. 3035 (16400') fiH = ± 0.13 1Ylz = ± 0.026

25B Aug. 75 1:56 500 10 mE = ± 0.75 mx = ± 138.8 SAgII 5000 ill 180/81 mN = ± 0.54 m y =±10

o. 2073 (16400') mH = ± 0.36 m, =± 0.07225C Sept. 74 1:58000 28 mH = ± 0.37 m, =± 0.042

15 UAgII 8800 ill 1356/57 ± 0.475 ± 0.0535

No. 3035 (29000')24D jan. 75 1:57000 26 fiH = ± 0.30 m, =± 0.036

15 UAgII 8400 ill 79/80No. 3047 (27750')

25B Aug. 75 1:58 000 28 fiH = ± 0.33 m, =± 0.03715 UAgI 8900 ill 118/19 ± 0.665 ± 0.0745

No. 6034 (29000')25B Aug. 75 1:58 000 28 mE = ± 0.66 mx =±l1

15 UAgl 8900 ill 119/20 mN = ± 0.70 m" = ± 12(29000') 1Ylz = ± 0.034

25C Sept. 74 1:88000 11 mE = ± 0.54 11~x = ± 615 UAgII 13400 ill 1273n4 mN = ± 0.92 m,,=±11No. 3035 (44 000') mH = ± 0.52 1Ylz = ± 0.039

25C Sept. 74 1:63 000 10 mE = ± 0.54 m = + 9x -21 NAgII 13400 ill 56/57 fiN = ± 0.82 m" = ± 13

(44000') fiH = ± 0.78 m, =± 0.06035C May 76 1:78000 44 fiH = ± 0.41 1Ylz = ± 0.035

15 UAgII 11 900 ill 68/69No. 3078 (39000')

1 Above mean ground level2 Root-mean-square error3 m1;. m;v, mJl in meters4 m,e. mll in the micrometers, m.= in °/00 of the flying height.S analytical evaluation

0.10 ~oo H

21NAG II 0

~15UAG 1/11 0

0 8.8SAG II •" •c0.~

~

0rn>~

.05 ~

~

c~ 0-:,--------- - ---0 0--------0-~ 0 0co

00

flying height

10 15 k..

FIG. 11. Elevation errors as a function of the flying height and the lens.

1252 PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSI G, 1977

15UAG II 6034 • 3047

2.03078 @ 3035 o

10

1.5

1.0flying height

--0 ------ ... __ 0-- ... 0

---- ------""'@>--"'-.o,

15 km

modelscale 1: 15 000 25 000 40 000

FIG. 12. Systematic errors in high-altitude photography can be compensatedby using an increased altitude or model scale number used in earth curvaturecorrection. The factor of enlargement K varies with the altitude. The circles inthe diagram indicate empirically derived values for four wide-angle lenses infour different Learjet photographic aircraft.

IMAGE QUALITY

The procedure and the results of theimage quality evaluation are shown in Fig­ures 15 and 16. The smallest visible imagedistance is influenced by many factors, e.g.,the contrast of the target to its neighborhood,the location in the image, the type of lensand the photographic emulsion, and others.Five different panels named S, R, D, H, andW were measured on 14 photographs at

scales between 1:56000 and 1:99 000. Theirlocation in the image was up to 130 mm tromthe center. This fact, however, influencedthe results only slightly.

Considering the measurements first, onecan see that in 75 percent of the cases thesmallest imaged distances are less than 30/-lom, that is, 1.8 m (6 ft) at the 1: 60000 photoscale. At the extremely small image scale of1:150 000 the panels with good contrast of

Deviation in2 m elevation Profile AG

"".... .........., ........ ....

'",/

'" --- 10 km

'"",

50 49 48 47 46 45 44

2 Deviation inm elevation Profile AH

................ _----"

....10' .... km

"50 49 48 47 46 45 44

FIG. 13. Example of the defom1ation of a high-altitude stereo model.

Data: Photographic aircraft LeaIjet 25-CFlying altitude 8900 mCamera RC 10 with

UAg II No. 3035Stereopair 1356/57Overlap 55 percentMeasurement in A 10 (dashed line)

and STK 1 (solidline) by D. Gut

Revised altitude forcorrecting earthcurvature will be 13200 m

The positions of the profiles are shown in Figure 14.

HIGH ALTITUDE PHOTOGRAPHY: ASPECTS AND RESULTS 1253

AF AG AH AJ

46

45

44

43

FIG. 14. Residual errors in elevation of a high-altitude stereo model.Data in Figure 13. Measurement in the A 10 stereoplotter

the Casa Grande test range (width b = 4.9 m)were still visible. Comparing the lens types,no diflerence can be detected for the threelenses. False color HIm shows equally goodresults as the panchromatic film. However, agreater percentage of targets were visible onthe false color film. Obviously, the lower res­olution of false color film is compensated bythe higher contrast of this HIm.

Inflight camera tilt. Camera tilt at themoment of exposure was determined duringmeasurement in the stereoplotter. For sevenstereomodels the maximum range of tilt wasbetween

-0.55" to +1.65" for lateral tilt (w)-0.30" to + 1.06" for longitudinal tilt (</J)

These values are relatively small. This factproves the stable flying altitude of jet air­craft. Small camera tilts will favorably influ­ence the measurements in analog stereo­plotters.

ApPLICATION OF HIGH-ALTITUDE

PHOTOGRAPHY IN TOPOGRAPHIC MAPPING

The enormous area coverage, combinedwith high geometric accuracy and ground res­olution of high-altitude photography, per­mits the use of new procedures in aerotrian­gulation, and in small-scale line and ortho­photo mapping. As early as 1969 the poten­tial of high-altitude aircraft for topographicmapping was impressively documented byR. E. Altenhofen with the help of practicalexamples. 3 In the meantime, new in­strumentation for picture-taking and mea­surements became available, e.g., hand­wheel and freehand driven precisionstereoplotters and digitally controlled or­thophoto printers of high resolution and highenlargement capability. With the help of thisnew instrumentation and the experiencegained from the evaluation of the photog-

Tar~et

f-0.81~

Photo~raph

Ib = 0.01 + 4.07 (7.62 - Y) values in m

7.62

FIG. 15. Detennination of the smallest visible image distance bymeans of a quadrilateral target. The length y of the imaged targetwill be measured, the width b will be detennined by calculation.Values in m.

1254 PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING, 1977

• Black & White rillllo false Color film

II'"I Iml'\ '" 1 :60 000

45

2.540

35 002.0

0

30

25 1.5•• 0

O'

20

1.015 ....10

0.5

tanJel S , o H W

lens UAG I UAG II SAG II

FIG. 16. Smallest visible image distance deter­mined for three types of lenses and two photo­graphic emulsions with the help of five differentpanels on 14 photographs of scales between 1:56000 and 1:99000. The panels measured were up to130 mm hom photograph center. The values arethe mean fi'om the four target pointers.

raphy over the Casa Grande test range, thecurrent procedures in small-scale mappingwill again require discussion.

AEROTRIANGULATION

With maximum Hying height and super­wide-angle lenses, the distance betweenfield control points may be increased. Whenusing wide-angle photographs of 1:80 000scale, precision stereoplotters or com­parators, and modern computationalmethods, a distance of about 60 km can bebridged. 4 The errors in planimetry and ele­vation of the control points should be small­er than 2 m. Maintaining this accuracy, thebridging distance can be extended to about100 km when using super-wide-anglephotographs taken from maxim um Hyingheight. Similarly, the number of photo­graphs is considerably reduced. An area of100 x 100 km2 , e.g., may be covered by only36 super-wide-angle photographs.

MEDIUM AND SMALL SCALE LINE MAPS

Line maps at scales between 1:50000 and1:25 000 had until recently been mappedfrom photography at scales which were small-

er than or the same as the map scale. Thelimitations in photo scale were conditionedby the service ceiling of small aircraft: and thepoor working climate in unpressurized cab­ins. When using small jet aircraft, the scalelimitations are determined by the adequacyof interpretation of small details and by thecontour interval to be mapped. But with thehelp of precisionplotters like the A 10 or thenew generation of analog stereoplotters suchas the Aviomap AMH, in which

• the measuring mark is conh'olled by hand­wheels and fi'eehand,

• the photograph is observed at high andchangeable magnification, and

• the plotting is done with the help of an au-tomatic table at the operator's side,

photography of smaller scales than beforecan be interpreted and accurately be mea­sured. When using the new generation ofwide-angle cameras and modern precisionstereoplotters, the photo scales listed inTable 2 seem to be applicable for open ter­rain.

When using modern super-wide-anglecameras, both map scales may be producedb'om 1: 100 '000 photography (b = 3 m, t:.h = 5m).

For planning purposes with low-accuracyrequirements, maps of larger scales such as1:5 000 could be mapped efficiently homhigh-altitude photography as well.

Orthophoto mapping. Orthophoto mapsare produced in large quantities at scales of1:25 000 (1:24 000) and 1:10 000. Theireconomic production is determined by,among other things, the ratio photo-to-mapscale. Modern orthophoto printers and goodphotography allow enlargement factors be­tween 4 X and 6 x. Limitations for the factorarise £i'om the service ceiling of the photo­graphic aircraft: and the smallest detail to beprinted and recognized by the user. In addi­tion to the wide-angle camera, the normal­angle camera with f = 21 cm is preferred insteep and wooded areas. For the map scalesconsidered, such a camera leads to altitudeswhich can be reached by jet aircraft only. Inopen and hilly terrain, super-wide-angle

TABLE 2. PROPOSED PHOTOSCALES FOR MEDIUM- AND SMALL-SCALE LINE MAPPING. THESE SCALES

WILL BE ACHIEVED FROM ALTITUDES OF 9 AND 12 km ABOVE TERRAIN, RESPECTIVELY. IN THE

LATTER CASE THE TERRAIN MAY STILL, BE Up TO 1.5 km ABOVE SEA LEVEL.

Map Scale

1:250001:50 000

Photo Scale

1:60000 - 8000080000

Smallest Visible ImageDistance b

2.0 - 2.5 m2.5m

Smallest ContourInterval M

4-5m5m

HIGH ALTITUDE PHOTOGRAPHY: ASPECTS AND RESULTS 1255

TABLE 3. PROPOSED PHOTO SCALES FOR MEDlUM- AND SMALL-SCALE ORTHOPHOTO MAPPING.

1:10 0001:25000

f= 88.5 mm

30 000 - 50 000100 000

f= 153 mm

40 000 - 60 00080000

f= 213 mm

6000060000

photographs can be utilized provided thatthe orthophoto printer accepts such photo­graphs and compensates for slope across thedirection of scanning. For the photomapsconsidered, the photo scales at optimal fieldangle listed in Table 3 seem to be practica­ble.

The camera should be selected accordingto the terrain. The scales were based on theassumption that the smallest detail to be rec­ognized in the photomap has a width of 2 mfor 1: 10 000 and 3 m for 1:25 000. Theplanimetric accuracy required for the mapswill easily be met by modern orthophotoprinters.

ACKNOWLEDGMENT

The authors are obligated to several per­sons for their support in this investigation.Dipl.-Ing. S. Heggli, Institute for Geodesyand Photogrammetry, E. T. H. Ziirich, per­formed the analytical point determinationfrom the stereocomparator data. Dipl.-Ing.Kreutzer, Wild Heerbrugg, calculated themodel deformations due to distortion, refrac-

tion, and window. The Optical CalculationDepartment of Wild Heerbrugg supportedthe authors in determining the image errorsdue to the bent window. Furthermore, Mr.Dipl.-Ing. Z. Pm'sic, E. T. H. Ziirich, shouldbe thanked for his help in comparator mea­surements; Mr. S. Blankenship of the GatesLealjet Company for the organization of thephotographic flights; and the Defense Map­ping Agency, Washington, D. c., for provid­ing the coordinates of the Casa Grande testrange.

REFERENCES

1. Bock, A. G., A breakthrough in high altitudephotographs from jet aircraft, Photogrammet­ric Engineering, Vo!. XXXIV, No.7, July1968.

2. Hiitte, Des Ingenieurs Taschenbuch, 28.AutI., S. 946, 1955.

3. Altenhofen, R. E., Application of high altitudephotographs in topographic mapping, PanAmerican Institute of Geography and His­tory, Washington, D. c., 1969

4. US Geological Survey, Annual report ofUSGS Cartographic Research, June 1976.

Articles for Next MonthU. V. Helava, The Analytical Plotter-Its Future.Gottfried Konecny, Software Aspects of Analytical Plotters.Dr. Bernard L. Y. Dubuisson, Why Analytical Plotters?Dr.-Ing. D. Hobbie, C-lOO PLANICOMP, the Analytical Stereoplotting System from

Carl Zeiss.Christian Vigneron, TRASTER 77: Matra Analytical Stereoplotter.Richard H. Seymour, The US-l Universal Stereoplotter.R. E. Kelly, P. R. H. McConnell, and S.]. Mildenberger, The Gestalt Photomapping System.S. Jack Friedman, The OMI Analytical Stereoplotter Model AP/C4.Prof. Giuseppe lnghilleri, The D.S.-Type Calileo Analytical Plotters.