plot_2D_line

% plots a 2D line from homogeneous vector h [3x1]
 
 Usage:
   plot_2D_line(h) 
        plots line h into current figure, using the max extend of
        current axis object
   plot_2D_line(h,x1,x2) 
        plots line h between points x1 and x2, which are
        either eucledian [2x1] or homogeneous [3x1]
   h = plot_2D_line(h,varargin) 
        returns line handle 

 06/17 Susanne Wenzel
 wenzel@igg.uni-bonn.de

0001 %% plots a 2D line from homogeneous vector h [3x1]
0002 %
0003 % Usage:
0004 %   plot_2D_line(h)
0005 %        plots line h into current figure, using the max extend of
0006 %        current axis object
0007 %   plot_2D_line(h,x1,x2)
0008 %        plots line h between points x1 and x2, which are
0009 %        either eucledian [2x1] or homogeneous [3x1]
0010 %   h = plot_2D_line(h,varargin)
0011 %        returns line handle
0012 %
0013 % 06/17 Susanne Wenzel
0014 % wenzel@igg.uni-bonn.de
0015 
0016 function varargout = plot_2D_line(h,varargin)
0017 
0018 N = @(x)x./x(3);
0019 
0020 h = h./norm(h(1:2));
0021 
0022 % get the current axis objects extend
0023 x_lim = get(gca,'xlim');
0024 y_lim = get(gca,'ylim');
0025        
0026 if nargin<3
0027     
0028     % generate standardline, footpoint or origin [+d, -d]
0029     d = norm([max(abs(x_lim)); max(abs(y_lim))]);
0030 
0031     S3 = [0 -1 0; 1 0 0; 0 0 0];
0032     % footpoint
0033     zl0 = N(calc_S(h)*S3*h);
0034     % direction
0035     phi = atan2(h(2),h(1));
0036     % start- and endpoint
0037     xs = zl0 + d*[cos(phi+pi/2);sin(phi+pi/2);0];
0038     xe = zl0 + d*[cos(phi-pi/2);sin(phi-pi/2);0];
0039 
0040 else
0041     % given startpoint
0042     xs = varargin{1};
0043     if numel(xs)<3, xs = N([xs;1]);end
0044     % footpoint onto the line, as startpoint for ploting
0045     xs = calc_S(h)* calc_S(xs)*diag([1,1,0])*h;
0046     
0047     % given endpoint
0048     xe = varargin{2};
0049     if numel(xe)<3, xe = N([xe;1]);end
0050     % footpoint onto the line, as endpoint for ploting
0051     xe = calc_S(h)* calc_S(xe)*diag([1,1,0])*h;
0052 
0053 end
0054 
0055 handle = plot([xs(1),xe(1)],[xs(2),xe(2)]);
0056 set(gca,'xlim',x_lim);
0057 set(gca,'ylim',y_lim);
0058 
0059 if nargout>0
0060     varargout{1} = handle;
0061 end
0062