Evaluation settings

The “Evaluation settings” window is used for selecting evaluation parameters. It can be accessed from start window and “Evaluation” window. Following are descriptions of the parameters.

Method & algorithm - PIV

For standard particle image velocimetry, parameters are determined in “Default settings” window.

Method & algorithm - HPIT

Hybrid particle image tracking. Press button “C” on the right to set parameters as below.

Position search method:
Method 1 – Selected to conduct a complete particle position search with given Minimal diameter, Maximal diameter and Gray value threshold; Press button “C” on the right to determine those parameters for particle image identification.
Method 2 – Selected to complete a simplified particle position search with given Minimal particle brightness and Particle image diameter; Press button “C” on the right to determine those parameters. A tracer filter can be used to improve the position search results.

Median filter:
Selected to conduct vector validation with an irregular median filter between the multi-pass interrogation iterations. The width and height of the filter window should be input.

Correct position with displacement - Selected so that the evaluation position is adjusted with particle image displacement.

Method & algorithm - PTV

Particle image tracking velocimetry.  Press button “C” on the right  to set parameters as below.

Particle image identification:
Dmin - Minimal particle image diameter;
Dmax - Maximal particle image diameter;
Margin - Zone width at four image edges where particles not be identified;
Threshold - Gray value threshold used to determine the contour of particle images;

Particle position
Center of mass - Particle image position determined with the center of mass of all the pixels of the particle ;
Center of brightness - Particle image position determined with a 5-point Gaussian fit at the high peak of the particle image brightness;
Fitted pattern center - Particle image position determined with a image pattern tracking algorithm;

Tracking parameters:
Weighting - Weighting coefficients in percentage;
Defo limit - Relative deformation limits for pairing two particle images;
Size - Pixel numbers contained in a particle image;
Brightness - Averaged gray value of a particle image;
Shape - Shape coefficient of a particle image;
Orientation - Orientation angle coefficient of a particle image.

Single PTV - Selected for tracking only one object in successive frames;

Error detection - Activated for detecting tracking errors with a reversibility check.

Method & algorithm - Ellipse window

Selected to activate an ellipse interrogation window.

Method & algorithm - Boundary mask

Selected to activate the boundary mask, when “B-mask” is imported.

Recording mode

Single recording (pair) - For evaluating a double exposed PIV recording or a single exposed PIV recording pair;

Recording group: individual evaluation - For evaluating a group of PIV recordings and saving individual vector maps (The PIV recordings in the group should be single frames);

Recording group: ensemble evaluation - For evaluating a group of PIV recordings with the average correlation method (The PIV recordings in the group should be single frames).

Exposure type

Single - Single exposed PIV image pair;

Double - Double exposed PIV image.

Flow direction

In case of double exposure, flow direction should be given as

E - East, i.e. directed to the right;

S - South, i.e. directed downwards;

W - West, i.e. directed to the left;

N - North, i.e. directed upwards.

Flow type

One phase - Single phase flow;

Two phase - Two phase flow;

Phase type

Continuous - Continuous phase;

Dispersed - Dispersed phase.

Initial window shift

(X,Y) - Interrogation window shifting started with a given value;

M1 - Interrogation window shifting started with valid vectors in memory 1;

M2 - Interrogation window shifting started with valid vectors in memory 2;

SPIV M1&2 button - Pushed down to activate window shift for stereo recording, i.e. M1 for camera A and M2 for camera B. This button is enabled when a stereo PIV recording or a group of stereo PIV recordings are loaded.

Distorted/stereo PIV calibration

None - No calibration;

Grid/vector - Selected to calibrate grid structure before evaluating the stereo or distorted PIV recordings; The displacement vectors will be transferred back to the original evaluation grid and calibrated after evaluation;

Image - Selected to calibrate stereo or distorted PIV recordings before evaluation;

Normal - Selected to use calibration function for normal camera;

A - Selected to use calibration function for stereo camera A;

B - Selected to use calibration function for stereo camera B.

Interrogation grid

Width - Width of the interrogation grid;

Height - Height of the interrogation grid;

Button “C” on the right is used to activate the changes.

Error limits [pixel]

Dx - Error toleration limit in pixels for horizontal particle image displacement component; 

Dy - Error toleration limit in pixels for vertical particle image displacement component.

Multi-pass interrogation setup

The evaluation can be conducted in two iteration steps: initial iteration step and final iteration step.

Iteration number - The sum of the initial iteration number and the final iteration number should be at least 1. The correlation-based tracking algorithm is used in the initial iteration step, and the correlation-based interrogation algorithm is in the final iteration step. To avoid too much evaluation time, the default setup for the initial iteration number is zero.

Window width - Width of the interrogation window;

Window height - Height of the interrogation window;

Search radius - Searching distance in 4 directions in the evaluation function plane. It must be one pixel larger than the maximum of particle image displacements to be determined.

Adaptive interrogation window

N - No window orientation is applied;

Grid - The long axis of the interrogation window is oriented to the direction of larger grid line distance;

Flow - The short axis of the interrogation window is oriented to the direction of larger velocity gradient.

Reshape - Checked to allow change of interrogation window shape during the multi-pass interrogation. When radio button “Grid” is select, the shape of the interrogation window is changed from square (round) to rectangular (Ellipse) shape according to the iteration number. When radio button “Flow” is selected, the shape of the interrogation window is changed from square (round) to rectangular (Ellipse) shape according to the velocity gradient.

Menu - File

Save settings - Used to save current evaluation parameters into a file;

Load settings - Used to import saved evaluation parameters from a file;

Preset 0 - Preset parameters for simple auto-correlation interrogation;

Preset 1 - Preset parameters for normal cross-correlation evaluation;

Close - Used to close “Evaluation settings” window.

Menu - Image filter

N - No image filter applied in evaluation;

SM - Smooth filter with given filter size applied in evaluation;

USM - Unsharp mask with given filter size applied in evaluation;

MPIV - Micro PIV filter with given filter size applied in evaluation;

RN - Regional normalization with given filter size and gray value threshold applied in evaluation;

PF - Particle filter applied in evaluation;

USM2 - Unsharp mask 2 with given filter size applied in evaluation;

Filter w - Width of the digital filter;

Filter h - Height of the digital filter;

Threshold - Gray value threshold for applying the RN filter.

Menu - More

This menu chose is used to open window “Default settings” for parameters that do not need to be changed in most cases.

Window shift & image correction:
FDIC - Selected to activate the forward difference image correction method (FDIC), i.e. image interpolation is only conducted in the second interrogation window to avoid large errors by too small particle images;
CDIC - Selected to activate the central difference image correction (CDIC) method, i.e. image correction is applied to both the 1st and 2nd evaluation samples;
CDI - Selected to activate central difference interrogation (CDI) method.

Image Correction algorithm:
N - No image correction;
4P - 4-point image correction method;
9P - 9-point image correction method.

Boundary improvement:
Extended grid - Checked to extend the interrogation grid out of the selected region to improve accuracy of evaluation results near to the boundary when the multi-pass image correction is applied.

Reference vectors:
N - No reference vector is selected;
M1 - Vectors in Memory 1 is selected as reference vectors;
M2 - Vectors in Memory 2 is selected as reference vectors.

Range limit validation parameters:
X - Limit of particle image displacement in x-direction;
Y - Limit of particle image displacement in y-direction;
None - Range limit validation not activated;
Absolute - Absolute range limit validation activated;
Relative - Relative (to a selected vector map) range limit validation activated. It works
when M1 or M2 is selected as initial window offset.  

Regular filter validation
Median filter -
Checked to activate regular median filter;
Vector correction - Checked to activate the target vector method to correct evaluation errors.

Vectors in Evaluation window:
Maximal display number -
Number vectors that can be displayed in Evaluation window;
Temporal vectors - Checked to display temporal vectors in Evaluation window;

Contours in group - Checked to display contours in Evaluation window, when a group of vector maps is imported.

Data export path
Press button “Change” to select a folder in hard disk for exporting some temporal data.

Image transformation method:
Auto -
Selected to automatically determine the image transformation method;
Straight - Checked to use straight line conservation method;

Poly - Checked to use polynomial fit method.

Output control:
Save vorticity instead of flag value -
Selected to output vorticity values in data file;

Save vectors by pressing ">" or "<" - Selected to save the vector maps in Evaluation window when “>“ and “>“ buttons are pressed.

 

 

 

Edpiv pE 2013 help