Small Format Aerial Photography

W.S. Warner, JORDFORSK, Centre for Soil and Environmental Research, Norway R. W.Graham, Consultant in Aerial Survey, Dorset, UK R.E. Read, Aerial Imaging Systems Ltd., Enschede, The Netherlands

Whittles Publishing Contents

Introduction xi The large format scene xi Digital small format aerial photography (DSFAP) xii Air film technology xiii Small format aerial photography xiii The economic case for using a small camera xiv The camera xiv The aircraft xv

PART 1 MAPPING AND MEASURING 1

1 Geometry of a single photograph 3 Scale 3 Average scale and point scale 4 Focal length • 4 Hyperfocal distance 5 Coordinate axes 6 Photo centres 7 Displacement 7 Topographic dispacement 8 Tilt displacement 9 A matter of balance 10 Scale = focal length/flying height 10 Photo coordinate axes and camera orientation Angle of depression and (omega) Scale variation and ij) (phi) or K (kappa) Orientation summary: the nine elements Ground coordinates to photo coordinates 14 Example terrain 15 Example map grid 15 Projecting map coordinates on the photo 16 Map grid superimposed on flat terrain Map grid superimposed on terrain with relief ... superimposed at different camera angles Summary 19

2 Geometry of stereo photography 20 Principle of stereoscopy 20 Parallax 21 Heighting accuracy: base:height ratio 21 Axis system 23 CONTENTS

x Parallax and y parallax 23 y Parallax 25 Summary 26

3 Mapping and measuring from single photographs 27 Map revision 27 Print reflectors 27 Slide projectors 29 Slides or prints? 29 Measuring 31 Vertical photography 31 Oblique photography 33 Analytical mapping and measuring 37 Operating procedures 39 Orientation Data collection What's a digitising tabled Summary 42

4 Stereoscopic mapping and measuring 44 Viewing the stereo pair 44 Lens stereoscope 44 Mirror stereoscope 48 Method 1: Two 35 mm slide projectors Method 2: A 70 mm slide projector The ten commandments of stereoscopic study 50 Methods of mapping and measuring 51 Map revision 51 Measurement 52 Projected slides 52 Enlarged prints 53 Stereometry 53 Analytical measurement systems 55 Simple digital instruments 56 Steroscopic plotting instruments 57 Summary 63

5 Practical considerations 64 Limitations of small cameras 64 Geometric instability 64 Imperfect lens system Unknown geometry: focal length and principal point Film flatness Apparent image motion Small format 69 Limited ground coverage Enlarging Balancing cost with accuracy 71 Accuracy and precision 71 A question of scale 72 Decision-making 73 Buyer beware 74 Summary 74

VI CONTENTS

6 Survey techniques for small format photography 76 Plotting the location of large scale photos 76 Measurements by aerial point sampling (APS) 78 Photo acquisition 78 Photo evaluation 79 Accuracy 82 Capturing ground control 83 Digitising control from a map 84 Digitising control from photographs 84 Estimated error and acceptable accuracy 85 Bundle adjustment for blocks of photographs 86 Controlled large scale photography 86 Precision altimeters 87 Fixed base systems 88

PART 2 AERIAL PHOTOGRAPHY OPERATIONS 91

7 Small format instruments and photographic films 93 Camera principles 93 SFAP with 35 mm cameras 95 Optimising the 35 mm image for SFAP 95 35 mm SLR cameras 96 The focal plane shutter Exposure metering Recommended cameras and lenses for 35 mm SFAP 99 Yashica ContaxRTSIII Rollei: Rolleiflex 3003 metric (35 mm) survey camera Leica R735 mm SLR Canon F-l AE and EOS-1 Minolta Dynax 7xi and Dynax 9xi Nikon F-80U and F4 Geometric Nikon FM2; F-801; F-601 conversions SFAP with (medium format) roll film cameras Advantages and disadvantages of roll film cameras for SFAP 103 Advantages Disadvantages Recommended cameras and lenses for roll film SFAP 104 Rollei Rolleiflex 6006 metric Hasselblad roll film cameras Hasselblad 500 EL/M Hasselblad 200 FC/M Hasselblad 553 ELX, 205 TCC and 201F Hasselblad MK 70 Vinten 70 mm reconnaissance cameras Vinten type 360 camera Vinten camera calibration: an example Vinten focal plane shutters Pentax 645 SLR cameras, including 645P and 645 V metric models Image quality and the total SFAP system 110 Subject 111 Camera lens 111 Film 112 Sensitometry Granularity: photographic noise

vii CONTENTS

Film resolution Film exposure and development Film types and their characteristics Film processing 117 Monochrome processing Film processing procedure 118 Print developers Colour processing Apparent image motion (AIM) 120 Print quality 121 Lens filters 122 Summary 122

8 Electronic (digital) imagery 124 Digital scanning 124 Scanner technology 125 Flatbed scanners Pixel resolution 127 Radiometric quality: brightness levels, AB 127 Pixel size and photogrammetric accuracy Direct digital acquisition: digital cameras 129 The charge coupled device (CCD) 130 Information theory for digital imagery 132 Digital cameras 133 Kodak Professional DCS 200 and DCS 420 dgital cameras 134 SFAP projects with the DCS 200 camera Digital image processing 136

9 Camera platforms 140 Platforms currently available 140 Balloons 141 Model aircraft 141 Microlight aircraft 142 Single-engined light aircraft 145 Twin-engined light aircraft 149 Economics 150 Fixed annual costs 150 Direct operating costs 151 Hourly costs 154

10 Camera mounts 155 Introduction 155 Types of camera mounts and controls 156 Heavy duty ball-and-socket camera mount 162 Non-rigid suspension mount 163 Rigid external mount 164 Internal mounting 167 Extended (door canopy) mounting 167 External door frame mounting 167 Intervalometers 168 Side sight 169 Stopwatch 171

via CONTENTS

11 Mission planning 173 Air survey calculations 173 Mapping calculations 173 PC software programs 175 Exposure calculations 175 Specimen SFAP mission plan 175 Using mission planning PC software 177 Block photography 178 Map preparation and flight pack 182 Flight maps 183 Lighting conditions 187 Mission logistics 190

12 Operational procedures 194 Pre-flight procedures 194 Camera 194 Camera mounting 194 Navigation sight 195 Mission planning and air traffic control 195 Preparing to fly 198 Pre-take-off checks 198 In-flight procedures 198 Photo management 202 Indexing 203 Monochrome film processing techniques 204 Processing control 204 The daylight film processing tank 206 Film processing 207 Film developers: types, techniques, temperatures and times 208 Monochrome printing 215 Colour processing 218

13 Air survey navigation 219 Basic flightline navigation 221 SFAP navigation methods: visual 231 Air survey turns 234 Direct survey turns 234 Survey U-turns 236 Global positioning systems (GPS) 237

PART 3 APPLICATIONS 245

14 Multispectral photography 247 Crop damage assessment 247 Conclusions 251

15 Urban survey 253 Introduction 253 SFAP survey for Bangkok metropolitan region 254 SFAP for large scale digital town mapping (Caloundra, Australia) 255 SFAP for producing a three-dimensional database 255 Small format pinpoint photography 256

IX CONTENTS

16 Small format photogrammetric surveys 257 A small format microlight survey (0.5 km2): Redruth, Cornwall, 1985 257 Ross SFS-3 sterocomparator 258 Carto Instruments: AP-190 analytical plotter 259 Adam Technology: MPS-2 microphotogrammetric system 260 Adam's SFAP system 261 Small format aerial photogrammetry for topographic surveys (Application Sheet No. 7) 262 Small format production of a three-dimensional database (Application Sheet No. 4) 263 Bundle adjustment for 35 mm oblique aerial photography 263 The LEO project 263 Small format mapping with GPS Survey Flight Management (SFM) 267 Small format mapping with SFM: Ohrdruf, Germany 269 Aerial survey without ground control 269

17 Small format aerial photography for natural resources 273 Forestry 273 Wildlife 275 Rangeland 276

18 Small format aerial photography for the environment 277 Geology and mining 277 Pollution control 277

19 Large scale map revision from digital cameras 279 Camera exposure and image quality 281 Soft copy photogrametry from the Kodak DCS-200 camera 281 Digital imagery at 1:17 000 photo-scale 282

Appendix 1 Computer programs (QBASIC) for aerial survey 287 (a) SURPLAN 288 (b) AIM 291 (c) SA1 292 (d) SZ1 293 (e) DITURNS 295 (f) UTURNS 297 (g) UTURN-A 299 (h) TAS 301 (i) TALT 302 (j) SS 303 Appendix 2 Unit conversions 305 Appendix 3 Side sight calculations 306 Appendix 4 Photo laboratory processing formulae 307 Appendix 5 Abbreviations, symbols and glossary 309 Abbreviations 309 Photogrammetric symbols 311 Glossary of photogrammetry 312 Appendix 6 Manufacturers and institutes 318 Appendix 7 Focal plane shutter testing 319 Appendix 8 Aircraft listing 321 Classified bibliography 327 Reference classifications 328 Bibliography: alphabetical listing 330 Index 345