Changes between Version 196 and Version 197 of UvmatHelp


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Timestamp:
Apr 18, 2015, 3:55:11 PM (6 years ago)
Author:
sommeria
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  • UvmatHelp

    v196 v197  
    589589-''' Appending  calibration points with the mouse: ''' Calibration points can be manually picked out by the mouse on the current image displayed by '''UVMAT''' (left button click). This requires the activation of the check box '''enable mouse'''. The image coordinates (in pixels) are picked by the mouse (the option 'blank' in the popup menu '''[transform_fct]''' is automatically selected when the mouse button is pressed). Zoom can be used to improve the precision, but must be desactivated for mouse selection (then move across the image by the key board directional arrows). Points can be accumulated from several images, using the key board short cuts 'p' and 'm' to move in the image series without the mouse.  A calibration point can be adjusted by selecting it with the mouse and moving it while pressing the left mouse button. The coordinates in pixel of the selected points get listed in the table '''[!ListCoord]''' of '''geometry_calib.fig'''.
    590590
    591 -''' Editing the coordinate table: ''' After mouse selection, the physical coordinates  must be introduced by editing the table. To make this task easier it is possible to export the table content on the Matlab command window by pressing '''[COPY PTS]''', and copy-paste a column on the table '''[!ListCoord]''' (the column below the introduction cell is filled). A single point can be removed by the 'backward' or 'suppr' keyboard command after selecting its line on the table. The whole set of points can be removed by pressing '''[CLEAR PT]'''. They can be also removed by pressing '''[STORE PT]''', then stored in a XML file (whose path and name is listed in '''[!ListCoordFiles]'''). Stored points can be retrieved by the menu bar command '''[Import/calibration points]'''.
     591-''' Editing the coordinate table: ''' After mouse selection, the physical coordinates  must be introduced by editing the table. To make this task easier it is possible to export the table content on the Matlab command window by pressing '''[EXPORT PTS]''', and copy-paste a column on the table '''[!ListCoord]''' (the column below the introduction cell is filled). A single point can be removed by the 'backward' or 'suppr' keyboard command after selecting its line on the table. The whole set of points can be removed by pressing '''[CLEAR PT]'''. They can be also removed by pressing '''[STORE PT]''', then stored in a XML file (whose path and name is listed in '''[!ListCoordFiles]'''). Stored points can be retrieved by the menu bar command '''[Import/calibration points]'''.
    592592
    593593-''' Creating a physical grid: ''' This tool '''[!Tools/Create grid]''' in the  menu bar command provides the set of physical coordinates of a cartesian grid, ranked line by line from the bottom. First pick the set of image coordinates with the mouse. Then launch  '''[!Tools/Create grid]''' and fill the first and last ''x'' and ''y'' values, as well as the meshes, in physical coordinates. These coordinates then fill the table '''[!ListCoord]'''.
     
    596596
    597597-''' Translation and rotation of calibration points: '''a translation or rotation (in physical space) can be introduced by the menu bar commands '''[!Tools/Translate points]''' and '''[!Tools/Rotate points]'''.  In the case of rotation, the origin of the rotation, as well as the angle (in degree) must be introduced. The resulting coordinates appear in the list '''[!ListCoord]'''.
     598
     599-''' Flipping coordinates: ''' a flip (inversion of coordinates) along $x$ or $y$ is performed by the menu bar command '''[!Tools/flip x]''' or '''[!Tools/flip x]''' respectively.
    598600
    599601-''' Recording calibration parameters: ''' Once the list of calibration points has been completed, press '''[APPLY]''', after selecting the appropriate option in '''[calib_type]''' (see the previous [#a8.1Generalities sub-section 8.1]). Note that the 3D options  require a sufficient number of calibration points (typically > 10) spread over the image with different values of z, or a tilted grid, see below. Calibration coefficients are recorded in the XML file <!ImaDoc> associated with the image currently opened by UVMAT. If previous calibration data already exist, the previous XML file is updated, but  the original one is preserved with the extension .xml~.  If no XML file already exists, it is created. The image transformation to phys coordinates can be directly seen on the '''uvmat.fig''' interface after completion of the command '''[APPLY]'''.
     
    844846
    845847=== 11.4 PATCH ===
    846 '''PATCH1: ''' interpolates the velocity values on a regular grid with a smoothing effect controlled by the parameter '''[num_!FieldSmooth]'''. The interpolation relies on the thin plate spline method, see [#tps: section 5.1]. This also provides the spatial derivatives (vorticity, divergence) needed for the refined processing civ2 (with option 'deformation'). 
     848'''PATCH1: ''' interpolates the velocity values on a regular grid with a smoothing effect controlled by the parameter '''[num_!FieldSmooth]'''. The interpolation relies on the thin plate spline method, see [#tps: section 5.1]. This also provides the spatial derivatives (vorticity, divergence) needed for the refined processing civ2 (with option 'deformation').
    847849
    848850The vectors which are too far from the smoothed field (erratic vectors) are eliminated (marked by an error flag), using a threshold set by '''[num_!MaxDiff]''' (expressed in pixel displacement). The interpolation is performed again by the program after this elimination.
     
    850852For fields involving many vectors, the thin plate spline method must be done by subdomains because of computer memory limitations. The parameter [num_!SubDomain] gives the typical number of vectors used to determine the partition in subdomains. The default value 1000 fits the memory capacity of usual computers.
    851853
    852 The button '''[TEST]''' in the '''[Patch]''' frame allows the user to quantify the difference between the '''[Civ]''' result ('civ1') and the smoothed velocity fields 'filter1' given by '''[Patch]'''. It opens a graph in a new '''Figure1''' plotting the rms difference between these two quantities (over the whole field) as a function of the smoothing parameter, varied around the value specified by '''[num_!FieldSmooth]''' parameter. This rms difference, expressed in pixel should be of the same order as the expected PIV error: the value 0.2 is indicated as an appropriate target for the choice of the corresponding smoothing parameter. A second curve indicates the proportion of vectors excluded by the criterion of excessive difference between the civ1 and filter1 fields. This criterion should apply only for erratic isolated vectors, so the corresponding proportion should not exceed a few percents. 
     854The button '''[TEST]''' in the '''[Patch]''' frame allows the user to quantify the difference between the '''[Civ]''' result ('civ1') and the smoothed velocity fields 'filter1' given by '''[Patch]'''. It opens a graph in a new '''Figure1''' plotting the rms difference between these two quantities (over the whole field) as a function of the smoothing parameter, varied around the value specified by '''[num_!FieldSmooth]''' parameter. This rms difference, expressed in pixel should be of the same order as the expected PIV error: the value 0.2 is indicated as an appropriate target for the choice of the corresponding smoothing parameter. A second curve indicates the proportion of vectors excluded by the criterion of excessive difference between the civ1 and filter1 fields. This criterion should apply only for erratic isolated vectors, so the corresponding proportion should not exceed a few percents.
    853855
    854856=== 11.5 CIV2 ===
     
    874876 * Perform usual PIV for each image series. For PIV near a straight wall, it may be useful to create a grid for each image series, corresponding to a common array of physical positions. This can be done by the upper menu bar option '''[!Tools/Make Grid]''' in the GUI '''uvmat''' (see section [#a9.2Grids Grids]).
    875877
    876  * To get the 3 velocity components in phys coordinates, combine the two PIV data series with the function 'civ2vel_3C' activated by the GUI ''series''. The data are assumed by default in a plane ''x,y'' (defined by a laser sheet). A transverse ''z'' displacement can be taken into account, introduced then in the third input line of the GUI ''series''. This ''z'' displacement can be obtained by stereo comparison of the two images (at the same time). 
    877 
    878 === 11.7 Topography measurement by image correlation from stereoscopic views === 
     878 * To get the 3 velocity components in phys coordinates, combine the two PIV data series with the function 'civ2vel_3C' activated by the GUI ''series''. The data are assumed by default in a plane ''x,y'' (defined by a laser sheet). A transverse ''z'' displacement can be taken into account, introduced then in the third input line of the GUI ''series''. This ''z'' displacement can be obtained by stereo comparison of the two images (at the same time).
     879
     880=== 11.7 Topography measurement by image correlation from stereoscopic views ===
    879881A displacement ''z(x,y)'' can be obtained by comparing two stereoscopic views (at the same time), using the function ''stereo_civ'' activated by the GUI '''series'''. This identifies corresponding points using image correlation, in the same way as ''civ''. A transform of the image to physical coordinates is performed as a first step to minimize the image difference between the two views. The final result is expressed as a set of ''(x,y,z)'' positions in physical coordinates (unlike PIV data which are expressed in image coordinates). See [attachment:3D_view.pdf] for full algorithm description.
    880  
    881882
    882883=== 11.8 Description of the velocity files: === #civdata
     
    11201121
    11211122=== Transform functions ===
    1122  * 'diff_vel': calculate the difference of two input velocity fields. 
     1123 * 'diff_vel': calculate the difference of two input velocity fields.
    11231124 * 'ima_color2BW': transform a color image to grey scale image
    11241125 * 'ima_filter': low-pass filter of an image (builtin filtering parameter).