Changes between Version 4 and Version 5 of Tutorial/ParticleImageVelocimetry


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Timestamp:
Sep 2, 2013, 7:30:18 PM (11 years ago)
Author:
sommeria
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  • Tutorial/ParticleImageVelocimetry

    v4 v5  
    77
    88== Launching PIV ==
    9 The PIV computation is accessed from uvmat by the upper bar command '''[Run/PIV]''', or from '''series''' by selecting the function '''civ_series'''. The name 'CIV' means '''C'''orrelation '''I'''maging '''V'''elocity to stress that the method relies on image correlation, which evaluates the displacement of image textures, not necessarily from particles. Note that an older GUI ''''civ'''' is also available, but not used here.
     9The PIV computation is accessed from uvmat by the upper bar command '''[Run/PIV]''', or from '''series''' by selecting the function '''civ_series'''. The name 'CIV' means '''C'''orrelation '''I'''maging '''V'''elocity to stress that the method relies on image correlation, which evaluates the displacement of image textures, not necessarily from particles. Note that an older GUI ''''civ'''' is also available, but it is obsolete and not used here.
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    11 A new GUI 'cic_input' now appears. In the menu '''[!ListCompareMode]''', keep the default option 'PIV'. Keep also the default option Di=0|1 for the image pair (menu tag '''[!ListPairCiv1]'''). Keep also the default parameters in the frame '''CIV1''' and press '''OK'''.
     11A new GUI 'civ_input' now appears. In the menu '''[!ListCompareMode]''', keep the default option 'PIV'. Keep also the default option 'Di=0|1' for the image pair (menu tag '''[!ListPairCiv1]'''). Keep also the default parameters in the frame '''CIV1''' and press '''OK'''.
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    13 The PIV operation depends on many parameters, but the default values proposed by the GUI provide a good first approach in many cases. Press '''[RUN] ''' to get the result. The button is then colored in grey until the computation is finished. The operation produces a  file with format netcdf, extension '''.nc''', in a subdirectory called ''''CIV' ''' by default. The file name ends with index string '_1-2' indicating that it results from images 1 and 2. The file name and its status is indicated in a new figure '''civ_status'''. Press the file name to open it with uvmat, or use the browser of '''uvmat'''.
     13The PIV operation depends on several parameters, but the default values proposed by the GUI provide a good first approach in many cases. Press '''[RUN] ''' to get the result. The button is then colored in grey until the computation is finished. The operation produces a  file with format netcdf, extension '''.nc''', in a subdirectory called ''''CIV' ''' by default. The file name ends with index string '_1-2' indicating that it results from images 1 and 2. The file name and its status is indicated in a new figure '''civ_status'''. Press the file name to open it with uvmat, or use the browser of '''uvmat'''.
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    1515<doc137|center>
    1616
    1717== Visualizing  the velocity fields ==
    18 To read the velocity field, open it with the GUI  ''''uvmat''''. Velocity vectors are displayed in the central window, while the histograms of each component are in the lower left windows, see Fig. [uvmat_fig]. The arrow length is automatically set by default. It can be adjusted by the edit box '''[!VecScale]''' in the  frame '''[Vectors']''' on the right hand side.
     18In ''''uvmat'''' velocity vectors are displayed in the central window, while the histograms of each component are in the lower left windows, see Fig. [uvmat_fig]. The arrow length is automatically set by default. It can be adjusted by the edit box '''[!VecScale]''' in the  frame '''[Vectors']''' on the right hand side.
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    2020The vector color indicates the quality of the image correlation maximum leading to each vector, blue is excellent, green average, red poor. The thresholds for such color display can be adjusted from 0 to 1 (perfect image correlation)  in the frame''' [Vectors]''', using the boxes '''[!ColCode1] ''' and '''[!ColCode2]''',  or equivalently by the corresponding  sliders '''[Slider1]''' and '''[Slider2] '''.
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    22 Vector color can also  represent another quantity, as chosen in the menu '''[!ColorScalar] ''' in the frame '''[Vectors]'''. For instance the vector length norm_vec can be used. Then a color continuous 64 color code is appropriate, as set in the menu '''[!ColorCode]'''. The color codes values between the valuies set by '''[!MinVec] ''' and '''[!MaxVec].'''
     22The black color indicates warning in the PIV calculation process. In this example, black vectors are indeed located on the edge, in zones outside the area of flow visualisation (this display can be desactivated by unselecting the box '''hide warn''' (tag '''[CheckHideWarning]''') in the frame '''Vectors''').
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    24 The position (x,y) and velocity components (U,V) can be displayed in the upper right text display window by moving the mouse over it.
     24The position (x,y) and velocity components (U,V) can be displayed in the upper right text display window by moving the mouse over it. The correlation 'C' and warning flag 'F' are also indicated. The warning flag is equal to 0 for good vectors while non-zero values indicate different cases of calculation problems.
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     26
     27== Other vector color representations ==
     28Vector color can also  represent another quantity, as chosen in the menu '''[!ColorScalar] ''' in the frame '''[Vectors]'''. For instance the vector length 'norm(U,V)' can be used. Then a color continuous 64 color code is appropriate, as set in the menu '''[!ColorCode]'''. The color codes values between the valuies set by '''[!MinVec] ''' and '''[!MaxVec].'''
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    2530
    2631== Derived fields ==