# Changes between Version 194 and Version 195 of UvmatHelp

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Timestamp:
Feb 21, 2015, 12:50:13 AM (6 years ago)
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• ## UvmatHelp

 v194 These functions can transform fields into polar coordinates, do image filtering, Fourier transform, signal analysis for a 1D input field... Other functions can be easily written using those as templates.  The  general form of such functions is  !DataOut=transform_fct(!DataIn,!XmlData,!DataIn_1,!XmlData_1) where Data is an input field object, as described in [#a5.2FieldrepresentationasMatlabstructure section 5.2], and !XmlData the content of the XML file Imadoc, as stored in the UVMAT GUI. !XmlData contains in particular the element [!GeometryCalib] containing the calibration parameters, see  [#a8.2TheGUIgeometry_calib.fig section 8.2]. === 4.7 Succession of operations: === === 4.7 Succession of operations === The following succession of operations is performed by '''uvmat.fig''': Fields may be alternatively obtained on a unstructured (grid-less) set of positions. The coordinates are then described by coordinate arrays X(nb_points), Y(nb_points), Z(nb_points). The corresponding field values are then represented as variables U(nb_point),V(nb_point) for each vector component, or alternatively by V(nb_points, j, i), where i, j possibly stand for vector or tensor components. - '''Thin plate shell (tps) interpolation:''' - '''Thin plate shell (tps) interpolation:''' #tps This is a multi-dimensional generalisation of the spline interpolation/smoothing, an optimum way to interpolate data with minimal  curvature of the interpolating function. The result at an interpolation position vector ${\bf r}$ is expressed in the form, (see ThinPlateShell). Any other element can be added, but will not be taken into account if they are not listed in  ''!ListGlobalAttribute'' or ''!ListVarName''. === 5.3 Conventions for attributes in field objects: === === 5.3 Conventions for attributes in field objects === - '''Global attributes active in UVMAT''': those are used for plot settings or data processing. === 11.4 PATCH === '''PATCH1: ''' interpolates the velocity values on a regular grid with a smoothing parameter '''[num_!FieldSmooth]'''. This also provides the spatial derivatives (vorticity, divergence) needed for the refined processing civ2. 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. The button '''[TEST]''' in the '''[Patch]''' frame allows the user to witness the difference between the '''[Civ]''' and '''[Patch]''' correlations due to smoothing. It opens a graph in '''Figure1''' showing the difference between the two correlation according to the value of the '''[num_!FieldSmooth]''' parameter. This difference should be lower than 0.2 to not distort the results. '''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. 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. === 11.5 CIV2 ===