Knowledgebase: Application Notes
Output Variables in Vic-2D and Vic-3D
Posted by Micah Simonsen, Last modified by Micah Simonsen on 13 October 2016 01:04 PM

 

During correlation and optional post-processing, Vic presents a wide range of output data available for 3D and contour plotting, extraction, and export. This application note gives an overview of commonly presented variables.

Output Variables

Always Present

  • X [mm] – metric position along the X-axis (by default, the horizontal axis).
  • Y [mm] – metric position along the Y-axis (by default, the vertical axis).
  • Z [mm] – metric position along the Z-axis (by default, the out-of-plane axis).
  • Sigma [pixel] – the 1-standard deviation confidence in the match, in pixels. 0 indicates a perfect match; higher numbers indicate a noise, excessive gradients, or possibly a failed match.
  • U [mm] – metric displacement along the X-axis, from the reference image. For the reference image, this value will always be 0.
  • V [mm] – metric displacement along the Y-axis.
  • W [mm] – metric displacement along the Z-axis.
  • x [pixel] – the X location, in the raw image, of the data point,
  • y [pixel] – the Y location, in the raw image, of the data point.
  • u [pixel] – the raw X-axis displacement between the reference image and a given image, in pixels. This is an internal variable which feeds into the triangulation algorithm to generate the 3D metric displacement data. Effectively, this variable is the output of a 2D correlation between the reference camera 0 image and the deformed camera 0 image.
  • v [pixel] – the raw Y-axis displacement between the reference image and a given image, in pixels.
  • q [pixel] – the raw X-axis disparity between the camera 0 image and camera 1 image, in pixels. This is an internal variable which feeds into the triangulation algorithm to generate the 3D metric shape data. Effectively, this variable is the output of a 2D correlation between the reference camera 0 image and a given camera 1 image.
  • r [pixel] – the raw Y-axis disparity between the camera 0 image and camera 1 image, in pixels.
  • q_ref [pixel] – this is the same as the computed X-axis disparity but is reserved for the software and cannot be edited by the user. This variable is used for retriangulation.
  • r_ref [pixel] – the reserved Y-axis disparity.

Strain Variables

  • exx [1] – strain in the X-direction. Positive numbers indicate tension; negative numbers indicate compression.
  • eyy [1] – strain in the Y-direction.
  • exy [1] – shear strain.
  • e1 [1] – the major principal strain.
  • e2 [1] – the minor principal strain.
  • gamma [1] – the principal strain angle, measure counterclockwise from the positive X-axis.

Velocity Variables

  • dU/dt [1] – the rate of change of the U-displacement; that is, the velocity of a given point in the X direction.
  • dV/dt [1] – velocity in the Y direction.
  • dW/dt [1] – velocity in the Z direction.
  • dExx/dt [1] – the rate of change of strain in X, or strain rate in X.
  • dEyy/dt [1] – the strain rate in Y.
  • dExy/dt [1] – the shear strain rate.
  • Note: principal strain rates are not calculated because principal strains, by nature, do not have a consistent reference frame from one image to the next.
Confidence Margins
  • Sigma_X [mm] – the 1-standard-deviation (67%) uncertainty in the X-axis.
  • Sigma_Y [mm] – the 1-standard-deviation (67%) uncertainty in the Y-axis.
  • Sigma_Z [mm] – the 1-standard-deviation (67%) uncertainty in the Z-axis.
2D-Specific Variables
  • x_c, y_c, u_c, v_c - these variables appear in the extraction dialog. If a scale calibration is present, they represent the scaled position and displacement. If no scale calibration is present, they're equal to the pixel values.
Deformed Variables (export only)
  • Xp – the deformed X value, equal to X+U. This is an option in the export dialog and is added for convenience.
  • Yp – the deformed Y value, equal to Y+V.
  • Zp – the deformed Z value, equal to Z+W.
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