Medium Format Digital Cameras: Standards and Specifications for Calibration and Stability Analysis

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Medium Format Digital CamerasStandards and
Specifications for Calibration and Stability
Analysis

• A. F. Habib
• Digital Photogrammetry Research Group
• http//dprg.geomatics.ucalgary.ca
• Department of Geomatics Engineering
• University of Calgary, Canada

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Introduction
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Operational Photogrammetric Systems

• Classification of digital cameras
  (photogrammetric perspective)
• Line Cameras (ADS 40)
• Large format digital frame cameras (??)
• Multi-head digital frame cameras (DMCTM, UltrCam,
  DiMAC 2.0)
• Medium-format Digital Cameras (MFDC)
• Mass-produced MFDC for mapping purposes (DSS,
  DiMAC Light)
• MFDC for mapping purposes from data providers
  (DAC 101)
• Amateur medium format digital cameras (AMFDC)

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MFDC from Data Providers

• DAC 101 Camera assembled by Selkirk Remote
  Sensing
• The camera utilizes a 60mm Rollei lens with a
  Rodenstock Apo-Sironar shutter and a 22 megapixel
  digital back (5440x4080 Imacon Ixpress 132
  Digital Back with 9µm pixel size)

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Amateur Medium-Format Digital Cameras
Kodak 14n
Canon EOS 1D
AMFDC
SONY 717
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Large Format Analog Cameras (LFAC)
WILD RC10
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Medium Format Digital Cameras (AMFDC)
SONY DSC F717
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MFDC Relevant Questions

• Is the use of amateur MFDC in mapping
  applications a temporary or permanent phenomenon?
  
• How to develop meaningful standards for
  evaluating the outcome from the calibration
  procedure?
• How to develop meaningful standards for
  evaluating the stability of the involved camera?
• Is there a flexibility in choosing the stability
  analysis tool, which is commensurate with the
  geo-referencing procedure to be implemented for
  this camera?

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Standards and Specification Philosophy

• Regulating the use of imaging systems in mapping
  applications can be done through either
• Having a government body (third party)
  responsible for the evaluation/calibration of the
  imaging systems.
• Widely adopted for analog cameras (USGS, NRCAN).
• Certifying the imaging systems.
• Suitable for digital imaging systems intended for
  mapping applications (DMCTM, ADS 40, UltrCam,
  DiMAC, DSS, etc.).
• Transferring the responsibility to the data
  provider after establishing a set of standards
  and specifications.
• Appropriate for AMFDC and MFDC from data
  providers.
• Calibration, stability analysis, achievable
  accuracy.

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Indoor Calibration Test Field
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Indoor Calibration Test Field
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Indoor Calibration Test Field
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Indoor Calibration Test Field
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Tested Cameras (Example)
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Tested Cameras (Example)
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Data Acquisition
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Calibration Images
Center High Low
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Calibration Images
Left High Low
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Calibration Images
Right High Low
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Calibration Specifications

• Variance component of unit weight
• Tier I lt 1 Pixel
• Tier II lt 1.5 Pixels
• Tier III lt N/A Pixels
• No correlation should exist among the estimated
  parameters
• Standard deviations of the estimated IOP
  parameters (xp, yp, c)
• Tier I lt 1 Pixel
• Tier II lt 1.5 Pixels
• Tier III lt N/A

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Stability Analysis Proposed Approach
Side View
Top View
P.C.II
P.C.I
cII
cI
Bundle I
Bundle II
Original Image Grid Points
Distortion-free Grid Points using IOPI
Distortion-free Grid Points using IOPII
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Stability Analysis Proposed Approach

• Method 1 Zero Rotation (ZROT)
• Same perspective center (no shift allowed)
• Parallel image coordinate systems (no rotation
  allowed)

P.C.
Ray from Bundle I
Ray from Bundle II
Offset
cI
cII
Original Image Points
Distortion-free Grid Point using IOPI
Distortion-free Grid Point using IOPII
Projected Grid Point of IOPII
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Stability Analysis Proposed Approach

• Method 2 Rotation (ROT)
• Same perspective center (no shift allowed)
• Rotation allowed

P.C. (0, 0, 0)
pI (xI, yI,-cI)
R (?, ?, ?)
pII (xII, yII,-cII)
Original Image Points
Distortion-free Grid Point using IOPI
Distortion-free Grid Point using IOPII
Projected Grid Point of IOPII
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Stability Analysis Proposed Approach

• Method 3 Single Photo Resection (SPR)
• Object space comparison
• Spatial and rotational offsets permitted

P.C.I
cI
cII
P.C.II
Original Image Points
Distortion-free Grid Point using IOPI
Distortion-free Grid Point using IOPII
Bundle I
Back-projected Object Points
Bundle II
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Stability Specifications

• The similarity measure (RMSE offset) value is
  computed to express the degree of similarity
  between the bundles from two sets of IOPs.
• The cameras must meet the following
  specifications to be deemed stable.
• Tier I lt 1 Pixel
• Tier II lt 1.5 Pixels
• Tier III N/A
• A software is available for the calibration and
  stability analysis procedures.

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MFDC Relevant Questions

• Can the stability analysis be used for evaluating
  the equivalency of different distortion models?
• Appropriate distortion models.
• Should the standards for the calibration and
  stability analysis be expressed in terms of image
  or object space units?
• What is the achievable accuracy from MFDC?
• Geo-referencing method (GCP, GNSS-assisted,
  GNSS/INSS).
• Number of tie points.
• What are the applications most suited for MFDC?
• Small blocks, in combination with LiDAR systems,
  in combination with high resolution satellite
  scenes.

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MFDC Aerial Mapping

• Kodak DCS-14n
• CMOS (4536x 3024)
• 50 mm Zeiss lens
• Pixel size 7.9x7.9 µm
• 12 Photos
• Flying height 1200 m
• GSD 0.20 meters

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MFDC Aerial Mapping
Federal University of Parana, Brazil
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MFDC Aerial Mapping
Number of Check Points Number of Check Points Mean (m) Standard dev. (m) RMSE (m)
17 Signalized Targets X 0.055 0.147 0.157
17 Signalized Targets Y 0.210 0.113 0.238
17 Signalized Targets Z 0.170 0.311 0.355
28 Natural Targets X 0.231 0.343 0.413
28 Natural Targets Y 0.201 0.141 0.246
28 Natural Targets Z -0.033 0.693 0.694
Root Mean Square Error Analysis
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MFDC Aerial Mapping
Orthophoto generated for Kodak (left) and RC10
(right) imagery
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MFDC, LiDAR Satellite Scenes
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Experimental Results Dataset
Lower Block
Lower LIDAR Scan
DSS Lower Block
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MFDC, LiDAR Satellite Scenes