Photogrammetry ' Lecture 9

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• Lecture 9 Content

• Orientation
• Inner
• Relative
• Absolute
• Orientation in analytical plotters

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• Orientation
• The formation of a stereo model to simulate the
  perspectives of the aerial camera at the time of
  exposure is by no means automatic, a strict
  setting-up procedure must be followed
• Each lamp on a traditional stereoplotter has to
  be focused and centered in order to project a
  close to perfect perspectives of light rays.
  This process is called inner orientation

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• Inner (Or Interior) Orientation
• The purpose of inner orientation is to recreate
  the geometry of rays at the time of exposure
• The procedure described here is with reference to
  an analogue streoplotter
• Inner orientation involves
• Correctly centering the two photographs in the
  stereoplotter in order to exactly locate the
  principal point
• Introduce the principal distance in the instrument

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• Relative Orientation
• The purpose of relative orientation is to
  re-create a stereo model of terrain in a smaller
  scale such that parallax is minimized
• Choose six readily discernable image points
  approximately in the positions shown below

Points 1 and 2 are near the principal points of
photos 1 and 2
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• The image processing method of relative
  orientation uses image processing to compare
  pixel groupings on the left and right photos and
  determine relative points from matched sets
• The two-image selection method of relative
  orientation offers selection of points appearing
  in the overlap area of only the two open images
• For the selection method of relative orientation,
  select relative points, removes parallax, and
  digitize each point

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• Each projector is capable of six movements
• Translations x, y, z
• Rotations ?, f, ?

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• Omega, Phi and Kappa define the orientation of
  the sensor when the imagery was captured.

This format of Omega, Phi, Kappa is the most
commonly used convention (ISPRS)
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• To eliminate the parallax at the 6 points (using
  an analogue stereoplotter) the following relative
  orientation task is done
• At point 1 by swing of projector 2
• At point 2 by swing of projector 1
• (Repeat i and ii until points 1 and 2 are free of
  parallax)
• At point 6 by tip of projector 1
• At point 4 by tilt of projector 1, over tilt by
  imparting about three times the amount of tilt
  required to remove parallax
• (Repeat until points 1,2,4 and 6 are free of
  parallax)
• At point 5 by tip of projector 2. Check for
  parallax at point 3, and repeat all movements
  until parallax is removed from all six points

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3
4

Photo 2
Photo 1
2
1


6
5


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• Each projector has six motions, giving 12 motions
  for the stereopair
• Relative orientation on an analogue stereoplotter
  usually require fifteen to sixty minutes to be
  completed (depending upon the experience of the
  operator)

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• Absolute Orientation
• The purpose is to bring the model to the desired
  scale and introduce the ground control
  information
• After inner and relative orientation the
  stereomodel is geometrically similar to the
  terrain but it must be brought to a known scale
  through the introduction of ground control
• Achieved by
• By changing the distance between the projectors
• Tilting the projectors together so that
  elevations are correctly measured

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• The analogue stereoplotter need to be scaled and
  leveled
• The required corrective rotation is resolved into
  two components ? and f
• Minimum of three control points are required
• In the analogue stereoplotter this is a manual
  iterative process (being careful not to disturb
  the relative orientations)
• Can take between 2 to 3 hours to get done

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• Exterior Orientation
• Exterior orientation is the process of gathering
  enough information about individual images to be
  able to calculate the ground coordinate of each
  image center
• The interior and relative orientations provide
  the information necessary to calculate exterior
  orientation
• Exterior orientation is usually calculated by a
  third-party aerotriangulation (AT) software
  package

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Height Measurements

• Achieved using the cursor in the stereo model

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Height Measurements
Location of point (X,Y Z)
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• Orientation in analytical plotters
• No mechanical motions are needed
• Inner, relative, and absolute orientations are
  performed computationaly
• Only the appropriate measurements have to be
  completed prior to computations
• Orientations are performed quicker and more
  precise than in the case of analogue
  stereoplotters
• Analytical plotters require image coordinates of
  the fudicial marks, camera calibration report,
  ground control points
• Least squares computations is done using the
  colinearity and coplanarity conditions to
  generate the stereo model

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Root Mean Square Error (RMSE)

• Indication of accuracy of transformation

RMS value in what units? PIXELS of original image
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• Present day analytical plotters are compact and
  are typically high end workstations
• At the Geomatics Program (TSU) use is made of
  Imagine software that is available on desktop
  PCs, and Data\EM workstation which is executed on
  a dedicated dual processor high end PC which is
  integrated with a customized version of the
  AutoCAD software.

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• The End