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SIFT-Aided Rectified 2D-DIC for Displacement and Strain Measurements in Asphalt Concrete Testing

Zehui Zhu, Imad L. Al-Qadi

Abstract

Two-dimensional digital image correlation (2D-DIC) is a widely used optical technique to measure displacement and strain during asphalt concrete (AC) testing. An accurate 2-D DIC measurement can only be achieved when the camera's principal axis is perpendicular to the planar specimen surface. However, this requirement may not be met during testing due to device constraints. This paper proposes a simple and reliable method to correct errors induced by non-perpendicularity. The method is based on image feature matching and rectification. No additional equipment is needed. A theoretical error analysis was conducted to quantify the effect of a non-perpendicular camera alignment on measurement accuracy. The proposed method was validated numerically using synthetic images and experimentally in an AC fracture test. It achieved relatively high accuracy, even under considerable camera rotation angle and large deformation. As a pre-processing technique, the proposed method showed promising performance in assisting the recently developed CrackPropNet for automated crack propagation measurement under a non-perpendicular camera alignment.

SIFT-Aided Rectified 2D-DIC for Displacement and Strain Measurements in Asphalt Concrete Testing

Abstract

Two-dimensional digital image correlation (2D-DIC) is a widely used optical technique to measure displacement and strain during asphalt concrete (AC) testing. An accurate 2-D DIC measurement can only be achieved when the camera's principal axis is perpendicular to the planar specimen surface. However, this requirement may not be met during testing due to device constraints. This paper proposes a simple and reliable method to correct errors induced by non-perpendicularity. The method is based on image feature matching and rectification. No additional equipment is needed. A theoretical error analysis was conducted to quantify the effect of a non-perpendicular camera alignment on measurement accuracy. The proposed method was validated numerically using synthetic images and experimentally in an AC fracture test. It achieved relatively high accuracy, even under considerable camera rotation angle and large deformation. As a pre-processing technique, the proposed method showed promising performance in assisting the recently developed CrackPropNet for automated crack propagation measurement under a non-perpendicular camera alignment.
Paper Structure (24 sections, 17 equations, 21 figures)

This paper contains 24 sections, 17 equations, 21 figures.

Table of Contents

  1. Introduction
  2. Two-Dimensional DIC Principle
  3. Research Objective
  4. Theoretical Error Analysis of A Non-Perpendicular Camera Alignment
  5. SIFT-Aided Rectified 2D-DIC
  6. Image Acquisition
  7. Key Point Extraction
  8. Key Point Matching
  9. Homography Matrix Estimation
  10. Image Rectification
  11. 2D-DIC Analysis
  12. Method Validation
  13. Numerical Validation
  14. Synthetic Images
  15. Experimental Setup
  16. ...and 9 more sections

Figures (21)

  • Figure 1: I-FIT testing devices.
  • Figure 2: 2-D DIC setup.
  • Figure 3: Establish correspondences between a reference and a deformed images pan2009two.
  • Figure 4: Camera's principal axis is not perpendicular to the planar specimen surface.
  • Figure 5: Top view of the pinhole camera model under non-perpendicular and perpendicular camera settings.
  • ...and 16 more figures