CIRGIS Imagery Project

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CIRGIS Imagery Project
2007-8
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There is a very complexphotogrammetric process
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Image Processing
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Orthophotography from Aerial Triangulation

• Aerial triangulation is the next step in the
  rectified image production process. This method
  is mandatory to establish the accurate ortho
  positions of the image pixel to ground-
  throughout both Counties, therefore removing all
  image distortion, and ensuring scale continuity
  across all tiles and selected project areas.

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Viewing a Stereo Pair
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Digital Elevation Model (DEM)

• After the AT process is complete and verified,
  stereo models are generated. Stereo models are
  two sequential DMC aerial frames that will be
  modeled in such a way that highly accurate three
  dimensional measurements can be calculatedusing
  both automated and manual modes.

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Digital Elevation Model (DEM)

• Photogrammetric Methods supporting
  Orthophotography, where accurate terrain model
  does not exist-traditionally
• AUTOCORRELATION option
• An approach where by stereo models are run
  through a pixel matching process (user -defined
  grid spacing) which determines like features
  (pixel number) among stereo pairs. DMIs team
  will perform autocorrelation processes with
  Intergraphs ImageStation Automatic Elevations
  (ISAE) software. ISAE, like ISAT, uses complex
  stereo pixel matching algorithms. Once a single
  matched pixel of interest is confirmed, ISAE
  calculates an elevation for it using
  photogrammetric principals.

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Digital Elevation Model (DEM)

• Our process involves taking each triangulated
  block, and processing the stereo models to
  produce surface points for each model. These
  surface points are placed into a MicroStation
  Design file for each stereo model. The design
  files are the clipped so that they do not overlap
  adjacent files and all points are reviewed and
  edited where necessary if not on terrain.

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Editing and QA/QC -Measurements

• Achieved using the cursor in the stereo model

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Tiling specs
Digital Imagery will be tiled and georeferenced
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QC Process Concerns
Check overall impression for color balance-Best
contrast used as reference image Histogram check
for full use of contrast range Seam lines
(between tiles and mosaic lines within tiles) are
well hidden-minimized tonal variations Check for
presence of ortho artifacts (smears, warped roads
and bridges, DEM spikes) Final RMSE check on
image positional accuracy
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Imagery Delivery Dates

• 1) City of Ventura 3 inch DELIVERED
• 2) City of Oxnard 3 inch 2-15-2008
• 3) 6" Imagery 3-25-2008
• 4) 1' Imagery 5-15-2008

Draft In review by City of Ventura and CIRGIS