CRSS/ASPRS 2007

Medium Format Digital Cameras:Standards and Specifications for

Calibration and Stability Analysis

A. F. HabibDigital Photogrammetry Research Group

http://dprg.geomatics.ucalgary.ca

Department of Geomatics EngineeringUniversity of Calgary, Canada

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Introduction

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• 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)

Operational Photogrammetric Systems

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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

SONY 717

Kodak 14n

Canon EOS 1D

AMFDC

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Large Format Analog Cameras (LFAC)

WILD RC10

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SONY DSC F717

Medium Format Digital Cameras (AMFDC)

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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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• 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.

Standards and Specification Philosophy

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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 < 1 Pixel– Tier II < 1.5 Pixels– Tier III < N/A Pixels

• No correlation should exist among the estimated parameters

• Standard deviations of the estimated IOP parameters (xp, yp, c):– Tier I < 1 Pixel– Tier II < 1.5 Pixels– Tier III < N/A

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cIcII

P.C.I

P.C.II

Original Image Grid PointsDistortion-free Grid Points using IOPI

Bundle IBundle II

Distortion-free Grid Points using IOPII

Side ViewTop View

Stability Analysis: Proposed Approach

≡?

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

P.C.

cI

cII

Offset

II

I

ccx2

2x

Ray from Bundle I

Ray from Bundle II

12 x

ccxII

I

Original Image Points

Distortion-free Grid Point using IOPI

Distortion-free Grid Point using IOPII

Projected Grid Point of IOPII

Stability Analysis: Proposed Approach

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

P.C. (0, 0, 0)

pI (xI, yI,-cI)

pII (xII, yII,-cII)

R (, , )

SpatialOffset

Original Image Points

Distortion-free Grid Point using IOPI

Distortion-free Grid Point using IOPII

Projected Grid Point of IOPII

Stability Analysis: Proposed Approach

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

cI

P.C.Ic

II P.C.II

Bundle IBundle II

Offset

Original Image Points

Distortion-free Grid Point using IOPI

Distortion-free Grid Point using IOPII

Back-projected Object Points

Stability Analysis: Proposed Approach

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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 < 1 Pixel– Tier II < 1.5 Pixels– Tier III : N/A

• A software is available for the calibration and stability analysis procedures.

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• 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.

MFDC: Relevant Questions

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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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Federal University of Parana, Brazil

MFDC & Aerial Mapping

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Number of Check Points Mean(m)

Standard dev. (m)

RMSE(m)

17 Signalized

Targets

X 0.055 0.147 0.157

Y 0.210 0.113 0.238

Z 0.170 0.311 0.355

28 Natural Targets

X 0.231 0.343 0.413

Y 0.201 0.141 0.246

Z -0.033 0.693 0.694

MFDC & Aerial Mapping

Root Mean Square Error Analysis

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Orthophoto generated for Kodak (left) and RC10 (right) imagery

MFDC & Aerial Mapping

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IKONOS stereo-pair

DSSthree six-image blocks with GPS position of

exposure stations

LIDAR data

up

middle

down

MFDC, LiDAR & Satellite Scenes

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Lower Block

DSS: Lower Block Lower LIDAR Scan

Experimental Results: Dataset

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0.000

5.000

10.000

15.000

20.000

25.000

30.000

35.000

0 1 2 3 4 5 6 7 8 9 10 15 40

Number of Control Points

RM

SE, m

NO Frames

Frame

GPS

Lines(45)

Lines (138)

Patches (45)

Patches (139)

N/A

MFDC, LiDAR & Satellite Scenes