AnaPIV

AnaPIV calculates two-dimensional vector fields from PIV images. The program implements

• iterative vector field correction (3 methods):
  • full-pixel window shift
  • window sub-pixel shift and deformation
  • image shift and deformation
• direct correlation with local normalization
• two-dimensional Gaussian fit
• Whittaker image interpolation
• interrogation area windowing
• universal outlier detection
• second peak validation
• correction of particle image intensity variations
• corrections of some bugs in the program

anapiv imga.ext imgb.ext px1 py1 dpx dpy iasx1 iasy1 iasx iasy method imax vel.out

anapiv imga.ext imgb.ext px1 py1 dpx dpy iasx1 iasy1 iasx iasy method imax vel.out upre vpre

where imga.ext and imgb.ext are the two consecutive PIV images (PCX, BMP, GIF, TGA, TPIC, PNG formats). px1 and py1 defines the first point (lower left corner) of the vector field grid. dpx and dpy define the grid spacing of the vector field. iasx1 and iasy1 define the interrogation area size of the first iteration and iasx and iasy define the interrogation area size of all following iterations. method is a number (0..2), which defines the PIV estimation method, with

• method=0 for full-pixel window shift
• method=1 for window sub-pixel shift and deformation
• method=2 for image shift and deformation

vel.out is the output file for the velocity/displacement estimes (ASCII) with the format

x y u v s

where x and y are the coordinates of the vector origin, u and v are the components of the velocity/displacement (all quantities in units of pixels) and s is the status, with

• s=0 for valid first peak estimate
• s=1 for valid second peak estimate
• s=2 for previous estimate
• s=3 for interpolated estimate

The optional parameters upre and vpre are pre-estimates of the displacements in x and y direction.

Background:

The full-pixel shift method is realized as an iterative (multi-step) method. The criterion to stop the iteration is the unchanged full-pixel shift. Furthermore it implements:

• direct correlation with local normalization as in High-precision sub-pixel interpolation in PIV/PTV image processing by H. Nobach, N. Damaschke and C. Tropea in Proc. 12th Int. Symp. on Appl. of Laser Techn. to Fluid Mechanics, Lisbon, Portugal, paper 24.1 (2004)
• no interrogation area window function

The iterative sub-pixel window shift and deformation method implements:

• FFT-based correlation
• triangular interrogation area window function (starting with the second iteration step)
• sub-pixel window shift and first-order deformations
• displacement gradients obtained from bi-linear interpolation including neighboring vectors
• Whittaker image interpolation (bi-cubic splines are implemented, requires re-compilation)

The iterative image shift and deformation method implements:

• FFT-based correlation
• triangular interrogation area window function (starting with the second iteration step)
• bi-cubic splines displacement interpolation
• Whittaker image interpolation (bi-cubic splines are implemented, requires re-compilation)

In all three cases:

• direct two-dimensional Gaussian fit as in Two-dimensional Gaussian regression for sub-pixel displacement estimation in particle image velocimetry or particle position estimation in particle tracking velocimetry by H. Nobach and M. Honkanen in in Exp. in Fluids (2005)
• Validation uses the Universal outlier detection for PIV data by J. Westerweel and F. Scarano in Exp. in Fluids (2005)
• Correction of individual particle image intensity variations as in Suppression of planar PIV errors due to particle intensity variations by H. Nobach in Proc. of the 15th Int. Symp. on Applications of Laser Techniques to Fluid Mechanics, Lisbon, Portugal, 05-08 July, 2010

The program is available pre-compiled for Mac OS X Intel or as a 32 bit application for Windows including its source code in Pascal.

Recommended compiler: Free Pascal.

	anapiv, executable program for Mac OS X on Intel
	anapiv.exe, executable program for 32 bit windows
	Sources (Pascal): anapiv.pas, airy2.pas, n2_complex.pas, n2_image.pas, n2_mathe.pas, n2_vector.pas, n2_matrix.pas, n2_splines.pas, n2_transforms.pas, pivtools2.pas. Recommended compiler: Free Pascal.