In PIV, particle images are correlated to obtain vector displacement information. Since the particle images themselves are random functions, the resulting correlation functions have random components which create a finite probability of having erroneous measurements which must be removed before the dataset can be used. Before the development of CleanVec, there were several cleanup programs already available. The problem with these programs is that validating, say, a 10⁴ vector field required an average of five hours. In order to accumulate enough data for good statistical measurements, approximately 10² vector fields are required. With a rate of five hours of cleanup time per vector field, it would take 500 hours (12 weeks) to validate 10² vector fields.

The goals of the CleanVec software development project were to

1. provide an interactive display to view PIV vector fields for analysis
2. develop manual vector cleanup software that does not fatigue the user
3. develop automated (mathematical) algorithms for vector cleanup that are robust
4. make a flexible system that can operate on PIV datasets from all types of flow fields
5. create batch processing capability to cleanup large numbers of vector fields

Here is a list of the more interesting features of CleanVec which make it an excellent vector validation program for PIV:

• Interactive Graphical Display. CleanVec provides full feedback to the user as to which vectors in the flow field are bad. Several different viewing modes allow the user to see bad vectors based on different criteria. The ability to view the active vector choice at each interrogation spot is also available. The Statistics window provides immediate information about the point underneath the cursor as the mouse is moved around the vector field.

• Assortment of Vector Removal and Replacement Tools. CleanVec provides several tools for the automatic removal and replacement of vectors, including
  
  
  • Remove vectors based on an allowable range for the total velocity vector
  • Remove vectors based on allowable tolerances for RMS fluctuations
  • Remove vectors based on signal-to-noise ratio threshold
  • Remove vectors based on allowable tolerances in neighborhood median magnitudes
  • Replace vectors with alternate choices corresponding to other correlation peaks
  • Interpolate holes using several different weighting functions
  • Smooth the vector field with a large selection of smoothing kernels
  
  One can also do manual vector removal and replacement for "fine" control.

• Full Control of Statistics. CleanVec gives the user full control over how statistics are computed, as well as how the mean velocity is subtracted. When computing global statistics, one may choose from the following averaging techniques:
  
  
  • X-Line Average
  • Y-Line Average
  • Area Average
  • User-Supplied Average (used to subtract a constant vector from the flow field)

• Batch Processing Capability. CleanVec can be run in batch mode using a script file created by the user. This allows unattended cleanup of a large number of vector fields. The script file can be generated either manually or via the record macro feature. When running CleanVec in batch mode, one also has the option of hiding the application. This provides developers of PIV interrogation software the ability to create a new CleanVec process, cleanup an image in batch mode that was just interrogated, and then display the cleaned-up image in their own program -- all without the user ever knowing CleanVec has been running.