function target = overlay(this,west,east,south,north,varargin)
%KML.OVERLAY(west, east, south, north) Places the image file (specified by the pair 
%  attribute 'file','image.png') as a ground overlay in the kml file. The corners  
%  of the image are given by inputs west, east, south and north. 
%  To make the overlay transparent, change the alpha portion of the color parameter
%  to a different hex value - eg.: 50% transparent, use KML.OVERLAY(...,'color','80FFFFFF')
%
%   Copyright 2012 Rafael Fernandes de Oliveira (rafael@rafael.aero)
%   $Revision: 1.1 $  $Date: 2013/06/03 20:05:48 $

    target = struct('type','','id','');

    [west,east,south,north] = this.checkUnit(west,east,south,north);
    
    p = inputParser;
       
    p.addRequired('west', @(a)isnumeric(a) && ~isempty(a) && numel(a)==1);
    p.addRequired('east', @(a)isnumeric(a) && ~isempty(a) && numel(a)==1);
    p.addRequired('south',@(a)isnumeric(a) && ~isempty(a) && numel(a)==1);
    p.addRequired('north',@(a)isnumeric(a) && ~isempty(a) && numel(a)==1);
    
    p.addParamValue('id',kml.getTempID('kml_overlay'),@ischar);
    p.addParamValue('name','kml_overlay',@ischar);
    p.addParamValue('description','',@ischar);
    p.addParamValue('visibility',true,@islogical);
    p.addParamValue('file','',@ischar);
    p.addParamValue('viewBoundScale',1,@(a)isnumeric(a) && numel(a)==1);
    p.addParamValue('color','FFFFFFFF',@(a)ischar(a) && numel(a)==8);
    p.addParamValue('altitude',1,@(a)isnumeric(a) &&~isempty(a) && numel(a)==1);
    p.addParamValue('rotation',0,@(a)isnumeric(a) &&~isempty(a) && numel(a)==1);
    p.addParamValue('drawOrder',0,@(a)isnumeric(a) &&~isempty(a) && numel(a)==1);
    p.addParamValue('altitudeMode','clampToGround',@(a)ismember(a,{'clampToGround','absolute'}));

    p.addParamValue('timeStamp','',@ischar);
    p.addParamValue('timeSpanBegin','',@ischar);
    p.addParamValue('timeSpanEnd','',@ischar);    
    
    p.parse(west,east,south,north,varargin{:});
    
    arg = p.Results;

    if isempty(arg.file)
        error('Missing file parameter')
    end
    
    arg.rotation = this.checkUnit(arg.rotation);
    
    overlay  = this.xml.createElement('GroundOverlay');
    llbox    = this.xml.createElement('LatLonBox');
    icon     = this.xml.createElement('Icon');

    overlay.setAttribute('id',arg.id);
    overlay.appendChild(this.textNode('name',arg.name));
    overlay.appendChild(this.textNode('color',arg.color));
    overlay.appendChild(this.textNode('visibility',num2str(arg.visibility)));
    overlay.appendChild(this.textNode('description',arg.description));
    overlay.appendChild(this.textNode('altitude',num2str(arg.altitude)));
    overlay.appendChild(this.textNode('altitudeMode',arg.altitudeMode));
    overlay.appendChild(this.textNode('drawOrder',num2str(arg.drawOrder)));

    if ~isempty(arg.timeStamp)
        timeStamp = this.xml.createElement('TimeStamp');
        timeStamp.appendChild(this.textNode('when',arg.timeStamp));
        overlay.appendChild(timeStamp);
    elseif ~isempty(arg.timeSpanBegin) || ~isempty(arg.timeSpanEnd)
        timeSpan = this.xml.createElement('TimeSpan');
        if ~isempty(arg.timeSpanBegin)
            timeSpan.appendChild(this.textNode('begin',arg.timeSpanBegin));
        end
        
        if ~isempty(arg.timeSpanEnd)
            timeSpan.appendChild(this.textNode('end',arg.timeSpanEnd));
        end
        overlay.appendChild(timeSpan);
    end    
    
    llbox.appendChild(this.textNode('north',    num2str(north)));
    llbox.appendChild(this.textNode('south',    num2str(south)));
    llbox.appendChild(this.textNode('east',     num2str(east)));
    llbox.appendChild(this.textNode('west',     num2str(west)));
    llbox.appendChild(this.textNode('rotation', num2str(arg.rotation)));

    icon.appendChild(this.textNode('href',arg.file));
    icon.appendChild(this.textNode('viewBoundScale',num2str(arg.viewBoundScale)));

    overlay.appendChild(llbox);
    overlay.appendChild(icon);
    this.doc.appendChild(overlay);
    
    target.id   = arg.id;
    target.type = 'GroundOverlay';
end