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Changes between Version 36 and Version 37 of UvmatHelp

Timestamp:: Jun 2, 2013, 11:42:06 PM (12 years ago)
Author:: sommeria
Comment:: --

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UvmatHelp

-                      v36
+                      v37
 {{{
                                    % number of bursts
 1024                            % image size npx npy
                                     % number of images per burst
                                      % not used
 .016667                          % time of exposure (in seconds)
 .860000 5.860000           % scaling pixel/cm x and y directions
 .860000 5.860000           % same
                                       % not used
 0.000000 30 60 30 1
 25.001003 30 60 30 1
  .........................
+                              % number of bursts
+1024                       % image size npx npy
+                               % number of images per burst
+                               % not used
+.016667                        % time of exposure (in seconds)
+.860000 5.860000               % scaling pixel/cm x and y directions
+.860000 5.860000               % same
+                               % not used
+0.000000 30 60 30 1           % for each line: burst number; time elapsed in second from the beginning; number of frames
+25.001003 30 60 30 1          % between image a and image b; number of frames between image b and image c; number of frames
+ .........................      % between image c and image d; image acquisition duration in frames
 424.999847 30 60 30 1
 450.000824 30 60 30 1 % for each line: burst number; time elapsed in second from the beginning; number of frames between image a and image b; number of frames between image b and image c; number of frames between image c and image d; image acquisition duration in frames.
+450.000824 30 60 30 1
 }}}
 -'''.cmx''' ascii text files containing the parameters sent by the GUI '''civ.fig''' to the CIV fortran programmes. Each velocity field named *.nc results from a parameter file *.cmx. It can be opened by the browser of '''uvmat.fig'''. In a later version of civx**, the .cmx file is replaced by a .xml ’CivDoc’ file.
 -'''.log''' ascii text files, containing information about processing in batch mode. Each velocity field named *.nc is associated with a  file *.log. A file *_patch.log is similarly produced by the ’patch’ program.  These files can be opened by the browser of '''uvmat.fig'''.
+ * '''.cmx''' ascii text files containing the parameters sent by the GUI '''civ.fig''' to the CIV fortran programmes. Each velocity field named *.nc results from a parameter file *.cmx. It can be opened by the browser of '''uvmat.fig'''. In a later version of civx**, the .cmx file is replaced by a .xml ’!CivDoc’ file.
+ * '''.log''' ascii text files, containing information about processing in batch mode. Each velocity field named *.nc is associated with a  file *.log. A file *_patch.log is similarly produced by the ’patch’ program.  These files can be opened by the browser of '''uvmat.fig'''.
 === 3.7 Data organisation in a  project: ===
+The package is designed to foster a good data organisation. The raw data from a project should be organised as  Project/Campaign/Experiment/DataSeries/data files.
+The package is designed to foster a good data organisation. The raw data from a project should be organised as:[[BR]]
+'''!Project/Campaign/Experiment/DataSeries/data files'''.
  * 'Project': contains all information from a project.
  * 'Campaign'' corresponds to a series of experiments obtained by varying a given set of physical parameters. A set of  parameter names (with units) is expected to be associated to a campaign. A project may involve several campaigns corresponding to different configurations, hence different relevant parameters. For a single configuration, 'Campaign' can be at the top of the data tree, without an additional 'Project' level. The uvmat package does not manage levels above 'Campaign'.
+ * 'Campaign' corresponds to a series of experiments obtained by varying a given set of physical parameters. A set of  parameter names (with units) is expected to be associated to a campaign. A project may involve several campaigns corresponding to different configurations, hence different relevant parameters. For a single configuration, 'Campaign' can be at the top of the data tree, without an additional 'Project' level. The uvmat package does not manage levels above 'Campaign'.
  * 'Experiment' is a directory containing all the data for a particular experiment, defined by a choice of values for the physical parameters.
  * 'DataSeries' contains an image series or movie from a camera, or more generally a data series from a device. Its name must correspond to the device and remain the same for all the experiments using this device. The results from data processing, as provided by 'civ' or 'series', are stored at the same level in a DataSeries directory, named from the source one with a extension specific to the processing program, for instance .civ for civ. ''
 '''Mirror data trees''' can be created to process a source data set in read only mode, to preserve the safety of the data source, and to allow several users to work in parallel without interference. This is done by opening the source Campaign with the menu bar option Open/browse campaign from uvmat. Select the source campaign directory with the browser. Then the GUI 'browse_data' appears. Then press 'create_mirror' and select the directory which must contain the mirror Campaign. A set of directory is then created for each experiment, in which are created symbolic  links to the DataSeries directories. Data processing then results in real DataSeries directories created in the Experiment directory.  An xml mirror.xml is created inside the directory mirror to mark its role; This xml file contains  the path and name of the source directory under the label <SourceDir>. The mirror directory can be regularly updated by pressing the button 'update_mirror'.
+ * '!DataSeries' contains an image series or movie from a camera, or more generally a data series from a device. Its name must correspond to the device and remain the same for all the experiments using this device. The results from data processing, as provided by 'civ' or 'series', are stored at the same level in a !DataSeries directory, named from the source one with a extension specific to the processing program, for instance .civ for civ. ''
+'''Mirror data trees''' can be created to process a source data set in read only mode, to preserve the safety of the data source, and to allow several users to work in parallel without interference. This is done by opening the source Campaign with the menu bar option Open/browse campaign from uvmat. Select the source campaign directory with the browser. Then the GUI 'browse_data' appears. Then press 'create_mirror' and select the directory which must contain the mirror Campaign. A set of directory is then created for each experiment, in which are created symbolic  links to the !DataSeries directories. Data processing then results in real !DataSeries directories created in the Experiment directory.  An xml mirror.xml is created inside the directory mirror to mark its role; This xml file contains  the path and name of the source directory under the label <!SourceDir>. The mirror directory can be regularly updated by pressing the button 'update_mirror'.
 == 4 Field display ==
 …
 === 4.1  Images and scalars: ===
   Images are matrices of integers, visualised by the Matlab function ''imagesc.m''.
+Images are matrices of integers, visualised by the Matlab function ''imagesc.m''.
 True color images are described by a matrix A(npy,npx,3) of integers between 0 and 255, the last index labeling the color component red, green or blue. They are displayed directly as color images.
 …
 <doc64|center>
 The greyscale images are described by a matrix A(npy,npx) of integers, whose range depends on the camera dynamics (0 to 255 for 8 bit images, 0 to 65535 for 16 bit images). They are represented with gray levels, according to the colorbar displayed on the right. The luminosity and contrast can be adjusted using the edit boxes '''[num_MinA]''' and '''[num_MaxA]''' on the right of the interface: the luminosity level set by '''[num_MinA]''' (and levels below) is represented as black, and the luminosity level set by '''[num_MaxA]''' (or levels above) as white. When the check box '''[CheckFixScalar]''' is not selected, these bounds are set automatically to the image minimum and maximum respectively. Then the image may appear dark if a single point is very bright, in that case a lower value must be set by '''[num_MaxA]'''. Greyscale images can be displayed with false colors, from blue to red, by unselecting the check box '''[CheckBW]'''.
+The greyscale images are described by a matrix A(npy,npx) of integers, whose range depends on the camera dynamics (0 to 255 for 8 bit images, 0 to 65535 for 16 bit images). They are represented with gray levels, according to the colorbar displayed on the right. The luminosity and contrast can be adjusted using the edit boxes '''[num_MinA]''' and '''[num_MaxA]''' on the right of the interface: the luminosity level set by '''[num_MinA]''' (and levels below) is represented as black, and the luminosity level set by '''[num_MaxA]''' (or levels above) as white. When the check box '''[!CheckFixScalar]''' is not selected, these bounds are set automatically to the image minimum and maximum respectively. Then the image may appear dark if a single point is very bright, in that case a lower value must be set by '''[num_MaxA]'''. Greyscale images can be displayed with false colors, from blue to red, by unselecting the check box '''[CheckBW]'''.
 Two images can be visually compared by switching back and forth between them as a short movie. This is quite useful to get a visual feeling of the image correlation for PIV. This effect is obtained by introducing two image indices in the edit boxes j1 and j2 (or i1 and i2), and selecting the button  '''[movie_pair] ''' (''''[<-->]'''') to switch between these two indices. The speed of the movie can be adjusted by the slider '''[speed]'''. Press '''[movie_pair] ''' again, or '''[STOP]''', to stop the motion.
 Scalar fields are  represented like B/W images, by default with a false color map ranging from blue (minimum values) to red (maximum), or as gray scale images by selecting the check box '''[BW]'''. Other color maps can be used by extracting the figure with the menu bar button '''[Export/extract figure]''', then using the standard  Matlab button '''[Edit/Colormap]''' in the figure menu bar.
 Scalar are represented by matrices with real ('double') values, unlike images which are integers. They can be alternatively defined with unstructured grid (see [section 5.3->#sec5.3]): they are then linearly interpolated on a regular grid before visualisation (a fairly slow process).
 Scalars (or image intensity) can be also represented with contour plots, by switching the popup menu '''[Contours] ''' from the setting 'mage' to the setting 'contours'. Contours for positive scalar values are in sold line while contours for negative values are dashed. The interval between contours can be set by the edit box '''[IncrA]'''.
+Scalar fields are  represented like greyscale images, by default with a false color map ranging from blue (minimum values) to red (maximum), or as gray scale images by selecting the check box '''[CheckBW]'''. Other color maps can be used by extracting the figure with the menu bar button '''[Export/extract figure]''', then using the standard  Matlab button '''[!Edit/Colormap]''' in the figure menu bar.
+Scalar are represented by matrices with real ('double') values, unlike images which are integers. They can be alternatively defined with unstructured grid (see [wiki:#a5.1Gridingofdata section 5.1]): they are then linearly interpolated on a regular grid before visualisation (a fairly slow process).
+Scalars (or image intensity) can be also represented with contour plots, by switching the popup menu '''[Contours] ''' from the setting 'image' to the setting 'contours'. Contours for positive scalar values are in sold line while contours for negative values are dashed. The interval between contours can be set by the edit box '''[num_IncrA]'''.
 === 4.2 Vectors: ===
 The vector fields are represented by arrows. The length of the arrows is automatically set when the check box'''[CheckFixVectors]''' is not selected, or it can be adjusted by the edit box '''[num_VecScale]'''.  For clarity of visualisation, the number of displayed vectors can be divided by 2 in each direction by selecting the check box '''[CheckDecimate4]'''.
+The vector fields are represented by arrows. The length of the arrows is automatically set when the check box'''[!CheckFixVectors]''' is not selected, or it can be adjusted by the edit box '''[num_VecScale]'''.  For clarity of visualisation, the number of displayed vectors can be divided by 2 or 4 in each direction by selecting the check box '''[CheckDecimate4]''', or '''[CheckDecimate16]''' respectively.
 Each vector has a color, ranging from blue to red, which can represent an associated  scalar value. In addition, black and magenta colors represent warning and error flags respectively. This color system is primarily designed for PIV data but can be used in other contexts as well.
 …
 <doc63|center>
+-'''Warning flags''': they indicate a vector resulting from a dubious  image correlation process, but not removed from the data set. Their display in black can be desactivated by selecting the check box '''[CheckHideWarning]'''.
+-'''Error flags''': they mark in magenta color vectors considered as false. These vectors are kept in the data set so that their elimination can be reversed, but they must not be taken into account for data processing. They can be removed for visualisation by selecting the check box '''[CheckHideFalse]'''.
+-'''Associated scalar: '''  for PIV velocity fields, the color  represents by default the image correlation, ranging from 0 to 1.  The red values correspond to poor correlations, green to fair values, and blue to good ones. The value range covered by each of the three colors is set by the pair of sliders  '''[Slider1]''' and '''[Slider2]''', or equivalently by the edit boxes '''[num_ColCode1]''' and '''[num_ColCode2]'''. Other color representations can be specified. '''[ColorScalar]''' sets the scalar used for color representation, for instance the vector norm 'norm_vec' or vorticity 'vort' (the list of available scalars is set by the function {calc_scal.m}).  '''[ColorCode] ''' sets the kind of color representation: -*'rgb':  color ranging from red, for the scalar value set by '''[num_MinVec]''', to blue, for the scalar value set by  '''[num_MaxVec]'''. The  color thresholds from red to green and green to blue are set by '''[ColCode1]''' and '''[ColCode2]''' respectively, or the sliders  '''[Slider1]''' and '''[Slider2]'''. By unselecting the check box [AutoVecColor], these thresholds can be set to match the min and max scalar values. -*'black' or 'white': set the color for all vectors -*'brg': same as rgb but in reverse order, with blue for the lowest scalar values.  -*'64 colors': quasi-continuous color representation, ranging from blue (for the scalar value given by '''[num_MinVec]''', to red, for the scalar value given by '''[num_MaxVec]'''.
+-'''Warning flags''': they indicate a vector resulting from a dubious  image correlation process, but not removed from the data set. Their display in black can be desactivated by selecting the check box '''[!CheckHideWarning]'''.
+-'''Error flags''': they mark in magenta color vectors considered as false. These vectors are kept in the data set so that their elimination can be reversed, but they must not be taken into account for data processing. They can be removed for visualisation by selecting the check box '''[!CheckHideFalse]'''.
+-'''Associated scalar: '''  for PIV velocity fields, the color  represents by default the image correlation, ranging from 0 to 1.  The red values correspond to poor correlations, green to fair values, and blue to good ones. The value range covered by each of the three colors is set by the pair of sliders  '''[Slider1]''' and '''[Slider2]''', or equivalently by the edit boxes '''[num_ColCode1]''' and '''[num_ColCode2]'''. Other color representations can be specified. '''[!ColorScalar]''' sets the scalar used for color representation, for instance the vector norm 'norm_vec' or vorticity 'vort' (the list of available scalars is set by the function {calc_scal.m}).  '''[ColorCode] ''' sets the kind of color representation:
+ * 'rgb':  color ranging from red, for the scalar value set by '''[num_MinVec]''', to blue, for the scalar value set by  '''[num_MaxVec]'''. The  color thresholds from red to green and green to blue are set by '''[ColCode1]''' and '''[ColCode2]''' respectively, or the sliders  '''[Slider1]''' and '''[Slider2]'''. By unselecting the check box [CheckFixVecColor], these thresholds can be set to match the min and max scalar values.
+ * 'black' or 'white': set the color for all vectors
+ * 'brg': same as rgb but in reverse order, with blue for the lowest scalar values.
+ * '64 colors': quasi-continuous color representation, ranging from blue (for the scalar value given by '''[num_MinVec]''', to red, for the scalar value given by '''[num_MaxVec]'''.
 -'''Mouse display''': when the mouse is moved over a vector, it is marked by a circle, and its features appear in the display text boxes on the upper right. These are  -* fist line: the position coordinates x, y, (z for 3D cases).  -* second line: the vector components -* third line: the vector index in the file, the values of the scalar (C), the warning flag (F) and the error flag (FF). The meaning of the flag values is given in [section 10.3->#sec10.3].
 -'''Manual editing of vectors''':  vectors can be manually set as 'false' by pressing '''[Edit/Vectors] ''' in the menu bar, then selecting the vector with the mouse. The selected vector becomes magenta. Inversely, if a magenta vector is selected, it is rehabilitated and retrieves its initial color.  The corrections are  recorded as false flags in the data file by pressing the pushbutton '''[record]'''.
+-'''Manual editing of vectors''':  vectors can be manually set as 'false' by pressing '''[!Edit/Vectors] ''' in the menu bar, then selecting the vector with the mouse. The selected vector becomes magenta. Inversely, if a magenta vector is selected, it is rehabilitated and retrieves its initial color.  The corrections are  recorded as false flags in the data file by pressing the pushbutton '''[record]'''.
 === 4.3 Histograms ===
 …
 === 4.6 Succession of operations: ===
+The following succession of operations is performed by '''uvmat.fig''': -'''File Reading:''' the input field is first read from the input file by the Matlab functions {imread.m}, {mmreader.m}, or {aviread.m} for images,  or the uvmat functions {nc2struct.m} or {read_civxdata.m} for netcdf files. -'''Second file reading:'''  The second input field is similarly read if selected. Note that it is kept in memory, so it is not read again if the file is unchanged (this is useful in the case of substraction of a fixed background for instance).  -'''Transform:''' by default the 'phys' option transforms each of the input fields from pixel to physical coordinates. This operation can also combine two input fields. -'''Histogram:''' This is obtained from the input field in transformed coordinates, or if applicable from the fields resulting from the two input fields. -'''Projection:''' on  the projection object selected in the menu '''[list_object_1]''', see [section 7->#get_field]. A second projection, on the object selected by '''[list_object_1]''', can be plotted in the anciillary figure '''view_field.fig'''. Function used: {proj_field.m}. -'''Field calculation:''' a scalar can be calculated from each of the input fields, as selected by the menu '''[Fields]'''. This is performed by the function {calc_field.m}. -'''Field comparison''': when two fields of the same nature are introduced, the difference is taken by the function {sub_field.m.}. This is skipped if the transform function has already led to a single field.  -'''Plotting:''' plot the results of projection. Function used: {plot_field.m}
+The following succession of operations is performed by '''uvmat.fig''':
+-'''File Reading:''' the input field is first read from the input file by the Matlab functions {imread.m}, {mmreader.m}, or {aviread.m} for images,  or the uvmat functions {nc2struct.m} or {read_civxdata.m} for netcdf files.
+-'''Second file reading:'''  The second input field is similarly read if selected. Note that it is kept in memory, so it is not read again if the file is unchanged (this is useful in the case of substraction of a fixed background for instance).  -'''Transform:''' by default the 'phys' option transforms each of the input fields from pixel to physical coordinates. This operation can also combine two input fields.
+-'''Histogram:''' This is obtained from the input field in transformed coordinates, or if applicable from the fields resulting from the two input fields.
+-'''Projection:''' on  the projection object selected in the menu '''[list_object_1]''', see [section 7->#get_field]. A second projection, on the object selected by '''[list_object_1]''', can be plotted in the anciillary figure '''view_field.fig'''. Function used: {proj_field.m}.
+-'''Field calculation:''' a scalar can be calculated from each of the input fields, as selected by the menu '''[Fields]'''. This is performed by the function {calc_field.m}.
+-'''Field comparison''': when two fields of the same nature are introduced, the difference is taken by the function {sub_field.m.}. This is skipped if the transform function has already led to a single field.
+-'''Plotting:''' plot the results of projection. Function used: {plot_field.m}
 == 5- Field objects: ==
-[sec5.1<-]
 === 5.1 Griding of data: ===
 <math> Physical fields can be defined either on regular grids, either scattered on an unstructured set of positions. Some measurements techniques, like PIV or particle tracking, provided unstructured data, while most methods of analysis require data  on a regular grid. This can be done by interpolation, defining a projection on a plane (with ProjMode='interp' or 'filter', see  [next section-> #set_object]).  The three possibilities of griding are defined as follows:
+Physical fields can be defined either on regular grids, either scattered on an unstructured set of positions. Some measurements techniques, like PIV or particle tracking, provided unstructured data, while most methods of analysis require data  on a regular grid. This can be done by interpolation, defining a projection on a plane (with ProjMode='interp' or 'filter', see  [next section-> #set_object]).  The three possibilities of griding are defined as follows:
 -'''Regular grid:'''
   Each field is then a multi-dimensional array V whose dimensions match the space dimensions.  Because of the grid regularity, the set of positions is fully defined by the coordinate value for the first and last index along each dimension of the array.
   -'''Structured orthogonal grid''':
+Each field is then a multi-dimensional array V whose dimensions match the space dimensions.  Because of the grid regularity, the set of positions is fully defined by the coordinate value for the first and last index along each dimension of the array.
+-'''Structured orthogonal grid''':
   Each field is again a multi-dimensional array V whose dimensions match the space dimensions, but the coordinates may not be regularly spaced, so they are represented as a monotonic 1D array variable with the same length as the corresponding dimension of V.  This is called a 'coordinate variable' (see section 7.1).
 …
 -'''Unstructured coordinates:'''
   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 V(nb_points, j, i), where i, j possibly stand for vector or tensor components.
+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 V(nb_points, j, i), where i, j possibly stand for vector or tensor components.
 -'''Thin plate shell (tps) interpolation:'''
 …
 === 5.3 Conventions for attributes in field objects: ===
+-'''Global attributes active in uvmat''' Those are used for plot settings or data processing. -*'Conventions':
+  ='uvmat': indicate that the conventions described here are followed
+='uvmat/civdata': indicate that the variables are named according to  [CIV data description->#civdata].  -*'CoordMesh': typical mesh for coordinates, used to define default projection grids and mouse selection action. Calculated automatically from the data if not specified. -*'CoordUnit': character string representing the unit for space coordinates. It is used to distinguish image coordinates (CoordUnit='pixel') and physical (for instance  CoordUnit='cm'). If 'CoordUnit' is defined,  [projection ->#set_object] will be allowed only on objects with the same 'CoordUnit', and plots will be done by default with axis option 'equal' (same scale for both axis). -*Dt: time interval for CIV data. It is used for calibration, to transform displacement into velocity.  -*Time: real number indicating the time of the field, used to obtain time series from data sets.  -*TimeUnit: character string representing the unit of time (consistently for Time, Dt and velocity).
+-'''Global attributes , unactive''' those are merely used for information purpose -*Project: recalls the project name -*Campaign: recalls the campaign name -*Experiment:  recalls the experiment name(s) of the raw data -*DataSeries:  recalls the device name (s), if defined, of the raw data   -*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.  -*ObjectCoord:  Coordinates defining a geometric object on which the data have been projected.  -*ObjectRangeX, ObjectRangeY, ObjectRangeZ : range of action of a projection object along each coordinate, see section 6.   -* '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.
+-'''Attributes of variables:''' -* Mesh: suggested step value to discretize the values of the variable, used to define the bins for histograms.  -* Role: it specifies the role of the variable arrays for plotting or processing programs, see below. if Role is not defined variables are considered by default as 'scalar'. -* Unit or 'units' (convention from [unidata->http://www.unidata.ucar.edu:]) : char string giving the unit of a variable, used  in plot axis labels (overset by global attributes 'CoordUnit' and 'TimeUnit' if defined).
+-'''The attribute 'Role':''' The following options are used for the attribute 'role': -* 'ancillary': information of secondary use, indicating for instance an error estimate of field variables within a field cell (omitted in plotting) -* 'coord_x', 'coord_y',  'coord_z': represents a  sets of unstructured coordinates x, y  and z for the field variables sharing the same dimension name. -* 'coord_tps': coordinates of thin plate shell (tps) centres used for spline interpolation. -* 'discrete': field with discrete values (no spatial interpolation), repesented with dots (no line) in 1D plots. -* 'errorflag': provides an error flag marking the field variables  as false or true within a field cell , default=0, no error. Different non zero values can mark different criteria of elimination, see [section 10.3->#sec10.3] for PIV data. Such flagging is reversible, since the data themselves are not lost. -* 'grad_x', 'grad_y', 'grad_z'  :represents the x, y or z  component of a contravariant vector** (like gradients). -* 'image_rgb': represents a color image. The last dimension of the array corresponds to the three color components 'rgb'. -* 'scalar': (default) represents a scalar field -* 'tensor': represents a tensor field whose components correspond to the two last   dimensions of the array.** -* vector: matrix whose last dimension states for the vector components.** -* 'vector_x', 'vector_y', 'vector_z'  : represents the x, y or z  component of a vector (covariant)  -* 'warnflag': provides a warning flag about the quality of data for the field variables within a field cell., default=0, no warning.
+-'''Global attributes active in uvmat''' Those are used for plot settings or data processing.
+-'Conventions':
+ * ='uvmat': indicate that the conventions described here are followed
+ * ='uvmat/civdata': indicate that the variables are named according to  [CIV data description->#civdata].
+-'CoordMesh': typical mesh for coordinates, used to define default projection grids and mouse selection action. Calculated automatically from the data if not specified.
+-'CoordUnit': character string representing the unit for space coordinates. It is used to distinguish image coordinates (CoordUnit='pixel') and physical (for instance  CoordUnit='cm'). If 'CoordUnit' is defined,  [projection ->#set_object] will be allowed only on objects with the same 'CoordUnit', and plots will be done by default with axis option 'equal' (same scale for both axis).
+-*Dt: time interval for CIV data. It is used for calibration, to transform displacement into velocity.
+-*Time: real number indicating the time of the field, used to obtain time series from data sets.
+-*TimeUnit: character string representing the unit of time (consistently for Time, Dt and velocity).
+-'''Global attributes , unactive''' those are merely used for information purpose
+-*Project: recalls the project name
+-*Campaign: recalls the campaign name
+-*Experiment:  recalls the experiment name(s) of the raw data
+-*DataSeries:  recalls the device name (s), if defined, of the raw data
+-*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.
+-*ObjectCoord:  Coordinates defining a geometric object on which the data have been projected.
+-*ObjectRangeX, ObjectRangeY, ObjectRangeZ : range of action of a projection object along each coordinate, see section 6.
+-* '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.
+-'''Attributes of variables:'''
+-* Mesh: suggested step value to discretize the values of the variable, used to define the bins for histograms.
+-* Role: it specifies the role of the variable arrays for plotting or processing programs, see below. if Role is not defined variables are considered by default as 'scalar'.
+-* Unit or 'units' (convention from [unidata->http://www.unidata.ucar.edu:]) : char string giving the unit of a variable, used  in plot axis labels (overset by global attributes 'CoordUnit' and 'TimeUnit' if defined).
+-'''The attribute 'Role':''' The following options are used for the attribute 'role':
+-* 'ancillary': information of secondary use, indicating for instance an error estimate of field variables within a field cell (omitted in plotting)
+-* 'coord_x', 'coord_y',  'coord_z': represents a  sets of unstructured coordinates x, y  and z for the field variables sharing the same dimension name.
+-* 'coord_tps': coordinates of thin plate shell (tps) centres used for spline interpolation.
+-* 'discrete': field with discrete values (no spatial interpolation), repesented with dots (no line) in 1D plots.
+-* 'errorflag': provides an error flag marking the field variables  as false or true within a field cell , default=0, no error. Different non zero values can mark different criteria of elimination, see [section 10.3->#sec10.3] for PIV data. Such flagging is reversible, since the data themselves are not lost.
+-* 'grad_x', 'grad_y', 'grad_z'  :represents the x, y or z  component of a contravariant vector** (like gradients).
+-* 'image_rgb': represents a color image. The last dimension of the array corresponds to the three color components 'rgb'. -* 'scalar': (default) represents a scalar field
+-* 'tensor': represents a tensor field whose components correspond to the two last   dimensions of the array.**
+-* vector: matrix whose last dimension states for the vector components.**
+-* 'vector_x', 'vector_y', 'vector_z'  : represents the x, y or z  component of a vector (covariant)
+-* 'warnflag': provides a warning flag about the quality of data for the field variables within a field cell., default=0, no warning.
 === 5.4 Field cells: ===