| 157 | | Information on image series is provided by a documentation file in the format xml. This file can include sections about image timing, geometric calibration, camera type and illumination. An xml file is a text file in which each element of information, or group of elements, is labelled by a tag. The list of tags and their hierarchical organisation is specified by a schema file (.xsd). The schema used for image documentation is ''!ImaDoc.xsd'', available in the uvmat package in a sub-directory ''/Schemas''. |
| | 157 | Information on image series is provided by a documentation file in the format xml. This file can include sections about image timing, geometric calibration, camera type and illumination. An xml file is a text file in which each element of information, or group of elements, is labelled by a tag. The list of tags and their hierarchical organisation is specified by a schema file (.xsd). The schema used for image documentation is ''!ImaDoc.xsd'', available in the uvmat package in a sub-directory ''/Schemas''. Simple templates of xml files are also provided there. A general introduction to the xml language and schemas is provided for instance in http://www.w3schools.com/xml. |
| 697 | | PIV can be performed by selecting the Matlab function ''civ_series'' as '''[!ActionName]''' in the GUI '''series'''. The same operations can be also performed with the older function ''civ.m'' running with the specific GUI '''civ.fig''', accessible from uvmat by the menu bar command '''[RUN/civ]'''. This older option is still used to run the fortran programs [CIVx]. |
| 698 | | |
| 699 | | -''' Opening the GUI: ''' The GUI '''civ.fig''' for PIV calculation can be directly opened by the command '>>civ' on the Matlab prompt. Then open an image or a documentation file (.xml ) with the file browser. ''' '''The''' ''' GUI '''civ.fig''' can be also directly opened from '''uvmat.fig''', by the menu bar command '''[RUN/civ]'''. A third way is just to open the Matlab image ({civ.fig} file) stored after each processing in the directory of the velocity fields. Then just edit it and run a new calculation. |
| | 697 | PIV can be performed by selecting the Matlab function ''civ_series'' as '''[!ActionName]''' in the GUI '''series.fig''': then the '''GUI civ_input''' appears to enter the processing parameters. An image file series must have been entered as input of '''series.fig''', or alternatively a Netcdf file resulting form a previous PIV processing (with conventions 'civdata'). |
| | 698 | |
| | 699 | An alternative possibility is to use the older Fortran program ''CivX'' from the GUI '''civ.fig'''. This can be called directly on the Matlab prompt, by typing ''>>civ'', or from uvmat by the menu bar command '''[RUN/PIV (old civ)]'''. |
| | 700 | |
| | 701 | '''-Modes of frame pair indexing''' |
| | 702 | A first menu '''[ListCompareMode]''' selects one among four modes of operation: |
| | 703 | * '''PIV''': makes image comparisons on sliding index pairs, as usual for measuring velocities by particle displacements. A second menu '''[ListPairMode]''' in the panel '''[PairIndices]''' then selects one among three possibilities (not always available depending on the file indexing): |
| | 704 | * ''pair j1-j2:'' selects a given j index pair (sometimes denoted by letter index) for the whole time series. This is the most common case for PIV. Pair selection is performed in the menu '''[ListPairCiv1]''' and '''[ListPairCiv2]''' for the second iteration Civ2, see below. If timing from an xml file [#a3.5Imagedocumentationfiles.xml ImaDoc] has been detected, this is indicated in the edit box '''[ImaDoc]''' and the corresponding time intervals are indicated (in ms). For some applications, this time interval may evolve in time, so that reference indices ref_i and ref_j are chosen for the display. |
| | 705 | * series (Di): selects a given index interval for the i index, around a set of reference i indices. The intervals are denoted Di=0|1, -1|1, -1|2, -2|2 ... , corresponding to the index pairs i|i+1, i-1|i+1, i-1|i+2, i-2|i+2 ...around each reference index i. Pair selection is then performed in the menu '''[ListPairCiv1]''' and '''[ListPairCiv2]''' like for 'pair j1-j2'. |
| | 706 | * series (Dj): same as series (Di) but with the j index. |
| | 707 | * '''displacement''': compare the current image to a fixed reference frame, as needed to measure the displacement with respect to this reference. The reference index (i index) is set by an edit box '''[num_OriginIndex]'''. |
| | 708 | * '''shift''': compares the corresponding images in two separate series, as need for stereographic views. The opening of a second file series is proposed by a browser when this option is selected. |
| | 709 | * '''PIV volume''' performs PIV in volumes for frame sequences with two indices i and j. The second index j is assumed to represent a position in a volume laser scan, while i represents time. Therefore PIV volume requires the selection '''series (Di)''' for '''[ListPairMode]'''. |
| | 710 | |
| | 711 | With all the options for pair comparisons, the set of reference frames is given by the master GUI '''series.fig'''. |
| 702 | | |
| 703 | | -''' Input file name and indexing: ''' The root name of the input file is displayed in the edit box '''[RootName]''', and a set of indices can be defined by the edit boxes '''[first_i] ''' (first index), '''[incr_i]''' (increment), '''[last_i ]'''(last index). The GUI offers a wide variety for the choice of image pairs to correlate. In the case of two file indices i and j, a mode for the choice of image pairs can be selected in the popup menu '''[mode]'''. -*'pairj1-j2': a given pair of j indices (or subscript a, b c...) can be chosen in the CIV1 menu '''[list_pair_civ1]''', while the corresponding indices i are set by '''[first_i] ''', '''[incr_i]''' , '''[last_i ]'''. -*'series(Di)': a sliding set of i index pairs is chosen by a set of {reference} indices i_ref given by '''[first_i] ''', '''[incr_i]''' , '''[last_i ]''' and a pair interval defined in '''[list_pair_civ1]''': the first choice 0|1 corresponds to the sliding pair i_ref|i_ref+1. the second choice -1|1 to the sliding pair i_ref-1|i_ref+1,...This mode is generally used with a single image series or movie, but it can be also used in volume scan, with a second index j chosen by '''[first_j] ''', '''[incr_j]''' , '''[last_j ]'''. -*'series(Dj)': operates like 'series(Di)', but with sliding j index pairs. -*comparing two image series: this is made possible by selecting 'displacement' in the popup menu '''[compare]''', which gives access to a browser for selecting the second image series. This second series can be reduced to a single reference image, if it contains no index. The displacement field with respect to this reference image is then obtained for successive times. -*stereo PIV: this option in the menu '''[compare]''' provides the three velocity components by comparing the stereoscopic views from two cameras, see [section 10.6->#sec10.6]. |
| 714 | | This series of operations is chosen by selecting the corresponding check boxes on the left, which give access to the corresponding parameter input panels. Note that the result of each of these operations is stored in the output netcdf file, so the process can be split in several runs. When an existing netcdf velocity file is opened, the GUI '''civ.fig''' is automaticaly configured to perform the next operation (fix1, patch1, civ2...) needed in the process. |
| | 724 | This series of operations is chosen by selecting the corresponding check boxes on the left of the GUI '''civ_series''', which give access to the corresponding parameter input panels. Note that the result of each of these operations is stored in the output netcdf file, so the process can be split in several runs. When an existing netcdf velocity file has been initially opened, the GUI '''civ.fig''' is automaticaly configured to perform the next operation (fix1, patch1, civ2...) needed in the process. |
| 717 | | The image pair is selected in the menu '''[list_pair_civ1]''', see sub-section 10.1. The time interval of the image pair must be chosen sufficiently small to provide a good correlation, and sufficiently large to provide good measurment precision: a displacement of 5-10 pixels is generally optimum. |
| 718 | | |
| 719 | | The time interval for each image pair is indicated in '''[list_pair_civ1]''' iif the information is made available, either from a movie file, or from a detected xml file (with the name !RootName.xml). The source of the timing information is indicated in the edit box '''[ImaDoc]'''. Examples of xml files are provides in /XML_SCHEMAS/ImaDoc_templates. In the absence of information, the file index is taken for the time. The time interval for a given index pair may change with time, so the time interval display is taken for given reference indices, given by '''[i_ref]''' and ''' [j_ref].'''. |
| 720 | | |
| 721 | | ('''[ibx], [iby])''' set the size (in pixels) of the 'correlation box', the sliding window used to get image correlations. '''[isx],[ isy]''' set the size of the 'search box' in which image correlation is calculated, see figure. This search box can be shifted with respect to the correlation box by parameters ([shift x],[shift_y]). This is useful in the presence of a known mean flow. |
| 722 | | |
| 723 | | The default value ibx=iby=(25,25) is generally good, use a larger size for images with few particles, use an elongated box , e.g. (11,41) , to optimise the resolution in one direction (for instance in a boundary layer). |
| 724 | | |
| 725 | | A parameter '''[rho(images)] ''' controls the smoothing of the image corelation curves used in civ, the default value 1 is generally used. |
| 726 | | |
| 727 | | The search parameters (isx, isy,shift x,y) can be estimated using the press button '''[search range]'''. First introduce the estimated minimum and maximum values of each velocity component u and v. The result depends on the time interval of the image pair. Change the selected image pair if the maximum displacement (ibsx-ibx)/2 is too small (lack of precision) or too large (bad image correlations and risks of false vectors). |
| | 727 | The time interval of the image pair (selected by '''[ListPairCiv1]''', see above) must be chosen sufficiently small to provide a good image correlation, and sufficiently large to provide good measurement precision: a displacement of 5-10 pixels is generally optimum. |
| | 728 | |
| | 729 | Examples of xml files are provides in /XML_SCHEMAS/ImaDoc_templates. |
| | 730 | |
| | 731 | ('''[num_CorrBoxSize_1,_2,_3], [iby])''' set the size (in pixels) of the 'correlation box', the sliding window used to get image correlations. '''[num_SearchBoxSize_1,_2,_3]''' set the size of the 'search box' in which image correlation is calculated, see figure. This search box can be shifted with respect to the correlation box by parameters ([num_SearchBoxShift_1,_2,_3]). This is useful in the presence of a known mean flow. The default value SearchBoxSize=(25,25) is generally good, use a larger size for images with few particles, use an elongated box , e.g. (11,41), to optimise the resolution in one direction (for instance in a boundary layer). |
| | 732 | |
| | 733 | A parameter '''[num_CorrSmooth] ''' controls the smoothing of the image corelation curves used in civ, the default value 1 is generally used. |
| | 734 | |
| | 735 | The search parameters (SearchBoxSize,earchBoxShift) can be estimated using the press button '''[search range]'''. First introduce the estimated minimum and maximum values of each velocity component u and v. The result depends on the time interval of the image pair. Change the selected image pair if the maximum displacement (ibsx-ibx)/2 is too small (lack of precision) or too large (bad image correlations and risks of false vectors). |
