Alexandra Karamitrou.ppt

509 views

Published on

Published in: Technology, Travel
0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total views
509
On SlideShare
0
From Embeds
0
Number of Embeds
5
Actions
Shares
0
Downloads
8
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide

Alexandra Karamitrou.ppt

  1. 1. Registration of Geophysical Images Alexandra A. Karamitrou Laboratory of Exploration Geophysics Aristotle University of Thessaloniki, Greece, Maria Petrou Informatics & Telematics Institute, CERTH, Thessaloniki, Greece Gregory N. Tsokas Laboratory of Exploration Geophysics Aristotle University of Thessaloniki, Greece [email_address] [email_address] [email_address] ARISTOTLE UNIVERSITY OF THESSALONIKI FACULTY OF SCIENCES
  2. 2. Geophysical methods The target is to increase the information obtained from the 2 original images independently. Archaeology Brizzolari et al., 1992a Garrison, 2003 Piro et al., 1998 Tsokas et al., 1994
  3. 3. Magnetic method Detect magnetic anomalies produced by the existence of buried features Instrument: Gradiometer sensors
  4. 4. Electrical method Determines the underground resistivity anomalies Electrodes that induce electric current Electrodes that measure the electric potential
  5. 5. Ruins from the temple of Dionisos ( 323 - 146 B.C ) Ceramic objects Archaeological area of Kampana (Maronia-NE Greece) Ancient Theater ( 323 - 146 B.C ) Mosaic floor from an aristocratic house ( 323 - 146 B.C )
  6. 6. Vertical Gradient of the local magnetic field Magnetic method Apparent Resistivity Electrical method Archaeological area of Kampana (Maronia-NE Greece) Tsokas G. et al., 2004
  7. 7. Ancient temple of Roman period (63 B.C – 476 A.D ) and an old Christian church ( 450–600 A.D ) Aero photography by Κ. Κ iriagos Archaeological area of Argos-Orestiko (West Greece)
  8. 8. Archaeological area of Argos-Orestiko (West Greece) Tsokas et al., 2006 Vertical Gradient of the local magnetic field Magnetic method Apparent Resistivity Electrical method
  9. 9. Vertical Gradient of the local magnetic field Magnetic method Apparent Resistivity Electrical method Archaeological area of Argos-Orestiko (West Greece) Tsokas et al., 2006
  10. 10. Need for Registration <ul><li>GPS have accuracies up to 5m, depending on the quality of the receiver, number of satellites etc. </li></ul><ul><li>Measurements in fields with different obstacles </li></ul>Electrical instrument Magnetic instrument <ul><li>Hand held instruments </li></ul><ul><li>the data may have errors due to </li></ul><ul><li>inaccuracies during the measurements </li></ul>
  11. 11. <ul><li>No rectangular images </li></ul><ul><li>Unchartered patches in the interior due to obstacles </li></ul>Image Preprocessing Original image Flagged image Flagging all the non-chartered pixels with a non realistic pixel value
  12. 12. Left column Vertical Gradient of the local magnetic field (magnetic method) Right column Apparent Resistivity (electrical method) Training set Test data
  13. 13. Image Registration We used a simplified version of the cost function (Kovalev V. A. and Petrou M., 1998) , where exhaustive search is used to find the parameters of the global translation that would maximize the mutual information between the pairs of images as well as their overlapping area. The geophysical images are from different modalities Mutual Information was used as a similarity measure Mutual Information 0.1204 Mutual Information 0.5431 Mutual Information 0.2234
  14. 14. In all three cases the results agreed exactly with the known shift between the pairs of images from their geographical coordinates. Preliminary registration of training set Preliminary registration of test data Registration Results
  15. 15. Affine Transformation Affine transformation is a linear 2-D geometric transformation which maps variables, through a linear combination of rotation, scaling and shearing followed by a translation, into new variables. Original Image Rotation Scaling Shearing
  16. 16. Proposed Methodology
  17. 17. “ continuity” parameter The Delaunay triangulation method (Delaunay B., 1934) was used. (2M+3)x(2M+3) Μ=1 25 pixels (2M+1)x(2M+1) Μ=1 9 pixels + + + + + + + + + + + + + + + + o o o o o o o o o x x x x x x x x x For the pixels at the places of the window with the maximum distortion, Selecting , the pixels at the periphery do not move much. Parameter is calculated as,
  18. 18. The randomly selected central pixel and the (2M+3)x(2M+3) window are selected with the condition that the whole window does not contain uncharted pixels.
  19. 19. Windows that succeed to increase the Mutual information Windows that fail to increase the Mutual information
  20. 20. Different values of mutual information for the training pair of images (Maronia). Argos Orestiko 1 st case Argos Orestiko 2 nd case Different values of mutual information for the two testing pair of images The algorithm was run without any change of the parameters for the 2 testing pair of images 0.5  0.98 0.57  0.76 0.8  1.46 Mutual Information Results
  21. 21. Transformed Images Results Archaeological area of Kampana Archaeological area of Argos Orestiko
  22. 22. Conclusions Registration method with rigid body translations succeeded to register the geophysical images in agreement with the geographical coordinates. Local inaccuracies (offsets) during the measurements degrade the overall mutual information between the images. We selected the parameters of the algorithm by using a training pair of images and then tested it, without changing these parameters on two other sets of images. In all cases the algorithm increased the mutual information between the images beyond the benchmark value of rigid body registration. We introduced a new efficient and effective semi-stochastic optimization algorithm which applies randomly distortions with randomly selected parameters, and accepts the changes only when they help increase the mutual information between the images. We proposed a method that applies local distortion while preserves the continuity of the grid.
  23. 23. Alexandra A. Karamitrou Laboratory of Exploration Geophysics Aristotle University of Thessaloniki, Greece, Maria Petrou Informatics & Telematics Institute, CERTH, Thessaloniki, Greece Gregory N. Tsokas Laboratory of Exploration Geophysics Aristotle University of Thessaloniki, Greece [email_address] [email_address] [email_address] Thank you for your attention !

×