26 January 2004 Trevis J. Gigliotti

1
Introduction

• Variety of measurements
• Angles
• Lengths
• Horizontal coordinates
• Majority of measurements on positive prints
• Variety of equipment and procedures
• Refinement of Measured Image Coordinates

2
Photo Coordinate System

• Must have fiducial marks to make measurements
• Photo coordinate system formed by joining
  opposite fiducial marks
• X-axis (positive) is the fiducial line parallel
  to flight direction
• Y-axis (positive) is located 90? counterclockwise
  from x-axis
• Z-axis is focal length
• Center of collimation
• Position of any object on a single photo is given
  by its corresponding rectangular coordinate value

3
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5
Trilaterative Method

• Background
• Obtains measured photo coordinates without
  scratching or cutting photographs
• Relies upon the calibrated coordinates of the
  fiducial marks
• Coordinates of photographic points calculated
  through basic principles of trigonometry
• Advantage of the method
• Increase in accuracy over simple scales
• Systematic measurement errors eliminated
• No cutting of imagery (can use more stable
  negatives)

6
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7
Measurement Equipment

• Low Accuracy
• Engineer scale
• Microrule
• Glass Scale
• High Accuracy
• Monocomparator
• Stereocomparator

8
Comparator Set-up
9
Systematic Error in Photo Measurements

• Major sources of systematic errors in measurement
• Failure of fiducials to intersect at principal
  point
• Shrinkage or expansion of photographic media
• Lens distortion
• Earth curvature
• Atmospheric refraction

10
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11
Photographic films Shrinkage

• Distortion is a function of
• Type of film
• Thickness
• Storage
• Drying practices
• Correction

12
Reseau Pattern
13
Radial Lens Distortion Correction

• Performed after corrections for shrinkage and
  expansion and reduction to principal point
• Three methods of correction
• Radial lens distortion curves
• Interpolating corrections from a table
• Approximating corrections through polynomials

14
Radial Lens Distortion Correction
15
Effects of Atmospheric Refraction
16
Effects of Earth Curvature