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1、 1 PHOTOGRAMMETRY 4 Basics of Photogrammetry4 Photography4 Photography - The First Part of Photogrammetry.4 Field of View.5 Focusing6 Exposure6 Camera Exposure .6 Background Exposure 6 Target Exposure.7 Metrology.8 Metrology - The Second Part of Photogrammetry.8 Triangulation.9 Resection10 Self-Cali
2、bration11 Bundle Adjustment12 Measuring Accuracy13 Scaling Photogrammetry.14 Multiple Scale Distances15 Long Scale Distances .16 MEASURING17 Measuring with V-STARS.17 Planning the Measurement 17 Questions You Should Ask: Remember “V-STARS“ 17 Defining a Coordinate System.19 MEASUREMENTS.21 Types of
3、Measurements.21 Initial and Repeat Measurements .22 Completely or Partially Overlapping Measurements.22 PLANNING FOR MEASUREMENTS25 Planning for Different Types of Measurements25 Design for Completely Overlapping Measurements .25 Design for Partially Overlapping Measurements.29 Design for “Left-Righ
4、t“ Measurements .29 Design for “Front-Back“ Measurements.31 Design for “Box“ Measurements34 Procedures for Different Types of Measurements.35 Final Planning Tips.36 Planning Summary and Checklist36 V-STARS Planning Checks: .36 TARGETING.38 Introduction to Targeting 38 Retro-reflector Targets and The
5、ir Characteristics38 Target Angle39 2 Target Thickness39 Target Sizes.39 Target Types.41 Individual self-adhesive stick on targets.41 Target Tape42 Hard-body tooling targets 42 Coded targets.44 Target Handling and Care44 Attaching the AutoBar 45 Attaching the Scale Bar(s)46 TARGETING SUMMARY AND CHE
6、CKLIST 47 Targeting Checklist.47 APPENDIX A .48 Frequently Asked Questions About Photogrammetry .48 How accurate is V-STARS? 48 How many photographs are needed for a measurement? 51 How many points are needed for a measurement?.52 Do I need scale for the measurement? .52 How do I compensate for scal
7、e changes due to temperature?53 Can the object move while it is being measured?53 Do I need to use special targets with the system?.54 What size should the targets be?.54 Can I use different size targets on the same measurement?.54 How obliquely can I view the targets?.55 Do I need to provide specia
8、l lighting for the system? .55 Do I have to consider the lighting during the measurement?.55 Do I need to know the camera location when I take a picture? .55 How steady must the camera be when taking a picture?.55 How far away do I have to get from the object to measure it?56 Where should I locate t
9、he camera to get a good measurement?56 How can I calibrate the camera and make sure the measurement is accurate?56 GLOSSARY58 AutoBar.58 AutoStart 58 CMM .58 Coded targets.59 Coded target nuggets59 Driveback.59 Field of View 59 Focusing .59 F-number60 Flash Synchronization.60 Free-format60 3 Orienta
10、tion.60 Photogrammetry.60 Resection .60 Retro-reflective61 RMS61 Scale bar61 SuperStart.61 Theodolite 61 XYZ File62 INDEX63 4 Photogrammetry Basics of Photogrammetry Before describing the operation of the V-STARS system, a brief introduction to photogrammetry is provided for those who are unfamiliar
11、 with the technology. Photogrammetry, as its name implies, is a 3-dimensional coordinate measuring technique that uses photographs as the fundamental medium for metrology (or measurement). The fundamental principle used by photogrammetry is triangulation. By taking photographs from at least two diff
12、erent locations, so-called “lines of sight“ can be developed from each camera to points on the object. These lines of sight (sometimes called rays owing to their optical nature) are mathematically intersected to produce the 3-dimensional coordinates of the points of interest. Triangulation is also t
13、he principle used by theodolites for coordinate measurement. If you are familiar with these instruments, you will find many similarities (and some differences) between photogrammetry and theodolites. Even closer to home, triangulation is also the way your two eyes work together to gauge distance (ca
14、lled depth perception). This primer is separated into two parts. Photography describes the photographic principles involved in photogrammetry, while Metrology describes the techniques for producing 3-dimensional coordinates from two-dimensional photographs. Photography Photography - The First Part o
15、f Photogrammetry Taking photographs is, of course, essential for making a photogrammetric measurement. To obtain the high accuracy, reliability and automation the system is capable of, photographs must be of the highest quality. Fortunately, because of the design of the system, photography with V-ST
16、ARS is actually simpler than film photography. The three main considerations for good photography are: 1. Field of View 2. Focusing 3. Exposure 5 Field of View The cameras field of view defines how much it sees and is a function of the focal length of the lens and the size (often called the format) of the digital sensor. For a given lens, a larger format sensor has a larger field of view. . Similarly, for a given size sensor, a shorter focal length lens has a wider field of view. The rel
