Changes between Version 195 and Version 196 of UvmatHelp


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Timestamp:
Feb 21, 2015, 1:10:39 AM (9 years ago)
Author:
sommeria
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  • UvmatHelp

    v195 v196  
    388388 * !ObjectStyle: ='points', 'line', 'plane', denotes the style of geometric object on which the data have been 'projected'. For instance a profiler project a physical field along a line.
    389389 * !ObjectCoord:  Coordinates defining a geometric object on which the data have been projected.
    390  * ObjectRangeX, ObjectRangeY, ObjectRangeZ : range of action of a projection object along each coordinate, see section 6.
     390 * ObjectRangeX, ObjectRangeY, ObjectRangeZ : range of action of a projection object along each coordinate, see [#ProjMode: section 6].
    391391 * 'long_name':(convention from [unidata->http://www.unidata.ucar.edu:]) a long descriptive name, could be used for labeling plots, for example. If a variable has no long_name attribute assigned, the variable name should be used as a default.
    392392
    … …  
    844844
    845845=== 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'). The vectors which are too far from the smoothed field (erratic vectors) can be eliminated, using a threshold expressed in pixel displacement (set by '''[num_!MaxDiff]'''). The thin plate spline method must be done by subdomains for computational saving. 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.
    847 
    848 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 a typical target for the choice of the corresponding smoothing parameter.
     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').
     847
     848The 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.
     849
     850For 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.
     851
     852The 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.
    849853
    850854=== 11.5 CIV2 ===
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    853857Image deformation and rotation can be introduced before calculating the correlations, by selecting '''[!CheckDeformation]'''. This option  is useful in the presence of strong shear or vorticity.
    854858
     859The image correlation can be visualised by pressing the button '''TEST''' in the same way as for civ1.
     860
    855861- '''FIX2:''' like '''[FIX1]''', except for a new possible flag value vec_F=4 which indicates that the difference between the estimator and the result is more than 1 pixel. This should be selected for excellent data (otherwise it may be too strict).
    856862
    857 - '''PATCH2:''' like '''[PATCH1]'''. Using the '''[TEST]''' option, we can here accept a difference between '''[Civ2]''' and '''[Patch2]''' higher than 0.2.
    858 
    859 Further iterations: improvements can be obtained by further iterations of the civ2-fix2-patch2 process. Open again the interface, and consider the previous civ2 result as the prior guess civ1. It will be recopied and relabelled as civ1 in the new NetCDF file produced.
     863- '''PATCH2:''' like '''[PATCH1]'''. Using the '''[TEST]''' option, we can similarly quantify the influence of the smoothing parameter. The recommended value of the rms difference between '''[Civ2]''' and '''[Patch2]''' (field 'filter2') is now set to 0.1, to safely avoid systematic distortion by smoothing in the final result.
     864
     865Further iterations: improvements can be obtained by further iterations of the civ2-fix2-patch2 process. Open again the interface, and consider the previous civ2 result as the prior guess civ1, and select the option civ3 in the checkbox which now appears in the panel civ2. The result will be put in a new NetCDF file, but still labelled as Civ2 field.
    860866
    861867=== 11.6 Stereoscopic 3C PIV === #sec11.6
    … …  
    868874 * 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]).
    869875
    870  * To get the 3 velocity components in phys coordinates, ombine 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).
     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).
    871877
    872878=== 11.7 Topography measurement by image correlation from stereoscopic views ===