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

Transcription

1 Medium-Format Digital Cameras: Standards and Specifications for Calibration and Stability Analysis A. F. Habib Digital Photogrammetry Research Group Department of Geomatics Engineering University of Calgary, Canada

2 Introduction 2

3 Operational Photogrammetric Systems Classification of digital cameras (photogrammetric perspective): Line Cameras (ADS 40) Large format digital frame cameras (??) Multi-head digital frame cameras (DMC TM, 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) 3

4 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) 4

5 Amateur Medium-Format Digital Cameras Kodak 14n Canon EOS 1D AMFDC 5 SONY 717

6 Large Format Analog Cameras (LFAC) WILD RC10 6

7 Medium Format Digital Cameras (AMFDC) SONY DSC F717 7

8 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? 8

9 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 (DMC TM, 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. 9

10 Indoor Calibration Test Field 10

11 Indoor Calibration Test Field 11

12 Indoor Calibration Test Field 12

13 Indoor Calibration Test Field 13

14 Tested Cameras (Example) 14

15 Tested Cameras (Example) 15

16 Data Acquisition 16

17 Calibration Images Center High & Low 17

18 Calibration Images Left High & Low 18

19 Calibration Images Right High & Low 19

20 Measurement Environment 20

21 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 21

22 Stability Analysis: Proposed Approach Top View Side View c I P.C. I? c II P.C. II Original Image Grid Points Bundle I Bundle II Distortion-free Grid Points using IOP I Distortion-free Grid Points using IOP II 22

23 Stability Analysis: Proposed Approach Method 1: Zero Rotation (ZROT) Same perspective center (no shift allowed) Parallel image coordinate systems (no rotation allowed) c I P.C. Offset x c I 2 x 1 cii Ray from Bundle I Ray from Bundle II c II Original Image Points x 2 c c I II Distortion-free Grid Point using IOP I Distortion-free Grid Point using IOP II x 2 Projected Grid Point of IOP II 23

24 Stability Analysis: Proposed Approach Method 2: Rotation (ROT) Same perspective center (no shift allowed) Rotation allowed P.C. (0, 0, 0) p I (x I, y I,-c I ) Spatial Offset R (ω, ϕ, κ) p II (x II, y II,-c II ) Original Image Points Distortion-free Grid Point using IOP I Distortion-free Grid Point using IOP II 24 Projected Grid Point of IOP II

25 Stability Analysis: Proposed Approach Method 3: Single Photo Resection (SPR) Object space comparison Spatial and rotational offsets permitted P.C. I c I c II P.C. II Offset Original Image Points Distortion-free Grid Point using IOP I Bundle I Bundle II Distortion-free Grid Point using IOP II Back-projected Object Points 25

26 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. 26

27 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. 27