FT_TOPOPLOTER plots the topographic distribution over the head
 of a 2-dimensional data representations such as the event-related
 fields or potentials or the power- or coherence spectrum.

 Use as
   ft_topoplotER(cfg, timelock)
 or
   ft_topoplotER(cfg, freq)

 The data can be an erp/erf produced by FT_TIMELOCKANALYSIS, a powerspectrum
 (without time dimension) produced by FT_FREQANALYSIS or a connectivityspectrum
 produced by FT_CONNECTIVITYANALYSIS.  Also, the output to FT_FREQSTATISTICS
 and FT_TIMELOCKSTATISTICS can be visualised.

 The configuration can have the following parameters
   cfg.parameter          = field that contains the data to be plotted as color, for example 'avg', 'powspctrm' or 'cohspctrm' (default is automatic)
   cfg.maskparameter      = field in the data to be used for masking of data. It should have alues between 0 and 1, where 0 corresponds to transparent.
   cfg.xlim               = limit for 1st dimension in data (e.g., time), can be 'maxmin' or [xmin xmax] (default = 'maxmin')
   cfg.zlim               = limits for color dimension, 'maxmin', 'maxabs', 'zeromax', 'minzero', or [zmin zmax] (default = 'maxmin')
   cfg.channel            = Nx1 cell-array with selection of channels (default = 'all'), see FT_CHANNELSELECTION for details
   cfg.refchannel         = name of reference channel for visualising connectivity, can be 'gui'
   cfg.baseline           = 'yes','no' or [time1 time2] (default = 'no'), see FT_TIMELOCKBASELINE or FT_FREQBASELINE
   cfg.baselinetype       = 'absolute' or 'relative' (default = 'absolute')
   cfg.trials             = 'all' or a selection given as a 1xN vector (default = 'all')
   cfg.colormap           = any sized colormap, see COLORMAP
   cfg.marker             = 'on', 'labels', 'numbers', 'off'
   cfg.markersymbol       = channel marker symbol (default = 'o')
   cfg.markercolor        = channel marker color (default = [0 0 0] (black))
   cfg.markersize         = channel marker size (default = 2)
   cfg.markerfontsize     = font size of channel labels (default = 8 pt)
   cfg.highlight          = 'off', 'on', 'labels', 'numbers'
   cfg.highlightchannel   =  Nx1 cell-array with selection of channels, or vector containing channel indices see FT_CHANNELSELECTION
   cfg.highlightsymbol    = highlight marker symbol (default = 'o')
   cfg.highlightcolor     = highlight marker color (default = [0 0 0] (black))
   cfg.highlightsize      = highlight marker size (default = 6)
   cfg.highlightfontsize  = highlight marker size (default = 8)
   cfg.hotkeys            = enables hotkeys (pageup/pagedown/m) for dynamic zoom and translation (ctrl+) of the color limits
   cfg.colorbar           = 'yes'
                            'no' (default)
                            'North'              inside plot box near top
                            'South'              inside bottom
                            'East'               inside right
                            'West'               inside left
                            'NorthOutside'       outside plot box near top
                            'SouthOutside'       outside bottom
                            'EastOutside'        outside right
                            'WestOutside'        outside left
   cfg.colorbartext       =  string indicating the text next to colorbar
   cfg.interplimits       = limits for interpolation (default = 'head')
                            'electrodes' to furthest electrode
                            'head' to edge of head
   cfg.interpolation      = 'linear','cubic','nearest','v4' (default = 'v4') see GRIDDATA
   cfg.style              = plot style (default = 'both')
                            'straight' colormap only
                            'contour' contour lines only
                            'both' (default) both colormap and contour lines
                            'fill' constant color between lines
                            'blank' only the head shape
   cfg.gridscale          = scaling grid size (default = 67)
                            determines resolution of figure
   cfg.shading            = 'flat' or 'interp' (default = 'flat')
   cfg.comment            = 'no', 'auto' or 'xlim' (default = 'auto')
                            'auto': date, xparam and zparam limits are printed
                            'xlim': only xparam limits are printed
   cfg.commentpos         = string or two numbers, position of the comment (default = 'leftbottom')
                            'lefttop' 'leftbottom' 'middletop' 'middlebottom' 'righttop' 'rightbottom'
                            'title' to place comment as title
                            'layout' to place comment as specified for COMNT in layout
                            [x y] coordinates
   cfg.interactive        = Interactive plot 'yes' or 'no' (default = 'yes')
                            In a interactive plot you can select areas and produce a new
                            interactive plot when a selected area is clicked. Multiple areas
                            can be selected by holding down the SHIFT key.
   cfg.directionality     = '', 'inflow' or 'outflow' specifies for
                            connectivity measures whether the inflow into a
                            node, or the outflow from a node is plotted. The
                            (default) behavior of this option depends on the dimor
                            of the input data (see below).
   cfg.layout             = specify the channel layout for plotting using one of
                            the supported ways (see below).
   cfg.interpolatenan     = string 'yes', 'no' (default = 'yes')
                            interpolate over channels containing NaNs

 For the plotting of directional connectivity data the cfg.directionality
 option determines what is plotted. The default value and the supported
 functionality depend on the dimord of the input data. If the input data
 is of dimord 'chan_chan_XXX', the value of directionality determines
 whether, given the reference channel(s), the columns (inflow), or rows
 (outflow) are selected for plotting. In this situation the default is
 'inflow'. Note that for undirected measures, inflow and outflow should
 give the same output. If the input data is of dimord 'chancmb_XXX', the
 value of directionality determines whether the rows in data.labelcmb are
 selected. With 'inflow' the rows are selected if the refchannel(s) occur in
 the right column, with 'outflow' the rows are selected if the
 refchannel(s) occur in the left column of the labelcmb-field. Default in
 this case is '', which means that all rows are selected in which the
 refchannel(s) occur. This is to robustly support linearly indexed
 undirected connectivity metrics. In the situation where undirected
 connectivity measures are linearly indexed, specifying 'inflow' or
 'outflow' can result in unexpected behavior.

 The layout defines how the channels are arranged. You can specify the
 layout in a variety of ways:
  - you can provide a pre-computed layout structure, see FT_PREPARE_LAYOUT
  - you can give the name of an ascii layout file with extension *.lay
  - you can give the name of an electrode file
  - you can give an electrode definition, i.e. "elec" structure
  - you can give a gradiometer definition, i.e. "grad" structure
 If you do not specify any of these and the data structure contains an
 electrode or gradiometer structure, that will be used for creating a
 layout. If you want to have more fine-grained control over the layout
 of the subplots, you should create your own layout file.

 See also FT_SINGLEPLOTER, FT_MULTIPLOTER, FT_SINGLEPLOTTFR, FT_MULTIPLOTTFR,
 FT_TOPOPLOTTFR, FT_PREPARE_LAYOUT